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"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

October 2012
Bulletin of Geosciences 87(4):767-813

October 2012
87(4):767-813

DOI:10.3140/bull.geosci.1335

Authors:

National Museum, Prague, Czech Republic

Sphooceras truncatum (Barrande, 1860), a Silurian straight-shelled cephalopod with a short finger-shaped shell, is one of a few cephalopods in which natural truncation of the apical part of the phragmocone from the rest of the conch is con-firmed. Periodic natural removal of the apical part of the shell (4 to 5 phragmocone chambers) preceded formation of a terminal callus and a calcareous plug closing the septal foramen. The apical callus probably originated by fusion of the truncation septum with episeptal deposits. These structures temporarily formed the new apex on which two additional calcareous layers had been secreted. A unique specimen preserves a colour pattern in the convex apical region, which proves that the shell in Sphooceras was temporarily completely surrounded by mantle extending from the body chamber, i.e. the cephalopod was at least temporarily endocochleate. The co-occurrence of different growth stages of S. truncatum together with one type of short juvenile orthoceracone shell, with a maximum of eight phragmocone chambers and a very small subglobular initial chamber indicates that these embryonic shells may belong to Sphooceras. Two other gen-era are discussed, both previously included in the family Sphooceratidae: Disjunctoceras Gnoli in Kiselev, 1992 and Andigenoceras Gnoli in Kiselev, 1992. The newly discovered thickening of the apex in "Disjunctoceras" disjunctum, the type species of Disjunctoceras, indicates that this species does not differ substantially from Sphooceras and should be reassigned to this genus. Similarly, representatives of Andigenoceras also possess characteristic features of Sphooceras. Sphooceras has many features characteristic for modern cephalopods: short, thin-walled, semi-internal shell; phragmocone reduced to only a few chambers; uncalcified connecting rings; apical callus (a structure analogous to the belemnite rostrum); retractor muscle scars situated dorsally; very small protoconch without cicatrix. In some excep-tionally well-preserved cephalopods with orthoceracone shell radula with seven rows of teeth were observed. All these features support the thesis that some straight-shelled cephalopods are evolutionarily closer to coleoids than nautiloids and their separation from nautiloids is legitimate. Vascular imprints on the surface of the cameral deposits provide fur-ther support for their primary origin and the existence of a cameral mantle. The character of cameral deposits in Sphooceras demonstrates that the systematic value of these structures in other straight-shelled cephalopods, a subject of controversy, has limited value. The morphology of Sphooceras also demonstrates that the boundary between endo-cochleate and ectocochleate cephalopods is not sharp, i.e. internalisation of the shell in cephalopods occurred repeatedly.

. Measurements of complete specimens of Sphooceras truncatum in mm. * Measured at the boundary phragmocene/body chamber.

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. Phragmocone chamber lengths in Sphooceras truncatum and Sphooceras disjunctum in mm.

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Sphooceras truncatum (Barrande, 1860); specimen NM L 40919a; Ludlow, latest Gorstian or earlier Ludfordian, Praha-Braník, Školní vrch, Kopanina Formation. • A-incomplete adult growth stage cut in median plane. Two last phragmocone chambers and adjacent part of body chamber not illustrated. The first chamber almost completely filled with cameral deposits showing radial structure in their outer part with graptolites Saetograptus fritschi within the siphuncle segment of third chamber, × 1.6. • B-the same specimen; detail of the outer shell wall; arrows indicate the place of truncation and (?)traces of a connecting ring, × 3.8.

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Relations between selected parameters of shell in Sphooceras truncatum; notice linear correlation between individual parameters.

…

+15

Sphooceras disjunctum (Barrande, 1868). • A, B, E-G-Praha-Butovice, Ludlow, Neodiversograptus nilssoni Zone, Kopanina Formation. • C, D-specimen NM L 40976, Praha-Butovice, Kační Quarry, Wenlock, Testograptus testis Subzone, Motol Formation. • A, B-specimen NM L 40975; almost complete young growth stage, partly exfoliated, with very low first chamber; dorsal and lateral views. • C, D-specimen NM L 40978, annular elevation; dorsal view. • E-the same specimen as in Fig. 8A; detail of detachment zone. • F, G-lectotype NM L 17549, illustrated by Barrande (1868, pl. 345, figs 11, 12); ventral and dorsal views. Scale bar: 10 mm.

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An endocochleate experiment

in the Silurian straight-shelled cephalopod Sphooceras

VOJTÌCH TUREK & TÌPÁN MANDA

Sphooceras truncatum (Barrande, 1860), a Silurian straight-shelled cephalopod with a short finger-shaped shell, is one

of a few cephalopods in which natural truncation of the apical part of the phragmocone from the rest of the conch is con-

firmed. Periodic natural removal of the apical part of the shell (4 to 5 phragmocone chambers) preceded formation of a

terminal callus and a calcareous plug closing the septal foramen. The apical callus probably originated by fusion of the

truncation septum with episeptal deposits. These structures temporarily formed the new apex on which two additional

calcareous layers had been secreted. A unique specimen preserves a colour pattern in the convex apical region, which

proves that the shell in Sphooceras was temporarily completely surrounded by mantle extending from the body chamber,

i.e. the cephalopod was at least temporarily endocochleate. The co-occurrence of different growth stages of S. truncatum

together with one type of short juvenile orthoceracone shell, with a maximum of eight phragmocone chambers and a

very small subglobular initial chamber indicates that these embryonic shells may belong to Sphooceras. Two other gen-

era are discussed, both previously included in the family Sphooceratidae: Disjunctoceras Gnoli in Kiselev, 1992 and

Andigenoceras Gnoli in Kiselev, 1992. The newly discovered thickening of the apex in “Disjunctoceras”disjunctum,

the type species of Disjunctoceras, indicates that this species does not differ substantially from Sphooceras and should

be reassigned to this genus.Similarly,representatives of Andigenoceras also possess characteristic features of

Sphooceras. Sphooceras has many features characteristic for modern cephalopods: short, thin-walled, semi-internal

shell; phragmocone reduced to only a few chambers; uncalcified connecting rings; apical callus (a structure analogous to

the belemnite rostrum); retractor muscle scars situated dorsally; very small protoconch without cicatrix. In some excep-

tionally well-preserved cephalopods with orthoceracone shell radula with seven rows of teeth were observed. All these

features support the thesis that some straight-shelled cephalopods are evolutionarily closer to coleoids than nautiloids

and their separation from nautiloids is legitimate. Vascular imprints on the surface of the cameral deposits provide fur-

ther support for their primary origin and the existence of a cameral mantle. The character of cameral deposits in

Sphooceras demonstrates that the systematic value of these structures in other straight-shelled cephalopods, a subject of

controversy, has limited value. The morphology of Sphooceras also demonstrates that the boundary between endo-

cochleate and ectocochleate cephalopods is not sharp, i.e. internalisation of the shell in cephalopods occurred repeatedly.

• Key words: Cephalopoda, Angusteradulata, Silurian, shell truncation, colour pattern, mantle extension, internal shell,

embryonic shell.

TUREK,V.&MANDA, Š. 2012. “An endocochleate experiment” in the Silurian straight-shelled cephalopod Sphooceras.

Bulletin of Geosciences 87(4), 767–813 (21 figures, 2 tables, 2 appendices). Czech Geological Survey, Prague. ISSN

1214-1119. Manuscript received January 6, 2012; accepted in revised form June 7, 2012; published online August 15,

2012; issued October 17, 2012.

Vojtěch Turek, Department of Palaeontology, National Museum, Cirkusová 1740, CZ-193 00 Praha 9, Czech Republic;

vojtech_turek@nm.cz • Štěpán Manda, Division of Regional Geology of Sedimentary Formations, Czech Geological

Survey, P.O. Box 85, Praha 011, 118 21, Czech Republic; stepan.manda@geology.cz

“Endocochlia”, frequently used as an older synonym of

the Coleoidea (Shevyrev 2005), represents a derived

clade of cephalopods, the history of which is reasonably

well documented from the Carboniferous onward (Flower

& Gordon 1959, Gordon 1964, Fuchs 2006, Doguzhaeva

et al. 2010, Mapes et al. 2010). The problematic middle

Cambrian Nectocaryx pteryx fossils from the Burgess

Shale, showing affinity to coleoids (Smith & Caron

2010), are neither cephalopods nor do they belong to the

stem group of cephalopods (Mazurek & Zatoń 2011, Krö-

ger et al. 2011).

From a formal standpoint, appearance of an external

mantle cover of the shell is considered a fundamental fea-

ture for classifying a cephalopod among coleoids. How-

ever, to find solid proof of the presence of an external man-

tle in Palaeozoic cephalopods is very complicated (Dzik

1984, Drushchits et al. 1978, Korn 2000). To regard a

cephalopod as a coleoid, one needs to look for the

767

DOI 10.3140/bull.geosci.1335

internalisation of the phragmocone. The presence of addi-

tional shell layers secreted on the outer surface of the pri-

mary shell wall by encasing soft tissues can provide evi-

dence of this. There are, however, some other characters

such as the narrow ventral siphuncle and some aspects of

the aperture, which may be of great importance for the

proper assignment of cephalopods to the coleoids.

The Silurian cephalopod Sphooceras truncatum (Bar-

rande, 1860), by its shell shape markedly resembling some

Mesozoic belemnites, displays such shell features. It dem-

onstrates that the boundary between the endocochleate and

the ectocochleate state has been crossed by more than one

group of cephalopods convergently. Morphological simi-

larity of some non-ammonoid cephalopods with ortho-

ceracone shell to some early coleoids (such as belemnites)

is remarkable, demonstrating convergence in both groups.

The shell of Sphooceras is short during the entire ontogeny

owing to periodical truncation – the natural removal of the

apical part of the shell during ontogeny. This interpretation

was first expressed, extensively discussed and supported

by precise illustrations by Barrande (1855, 1860, 1868,

1870, 1874, 1877) in Orthoceras truncatum Barrande,

1860.This phenomenon was also found in some other

cephalopods and was widely accepted by other cephalopod

workers (e.g. Blake 1882; Schröder 1888; Flower 1941,

1964; Furnish et al. 1962; Teichert 1964; Gnoli & Kiselev

1994).

Teichert (1964, p. 48) summarised Barrande’s ideas

(1855, 1860, 1877) concerning the mechanism of trunca-

tion in Sphooceras: “The truncation was preceded by for-

mation of a calcareous plug in the siphuncle at the septum

of truncation. The posterior portion of the phragmocone

was thus cut off from metabolic processes, resulting in pro-

gressive (dis)solution and final destruction of the decidu-

ous portion.” Barrande (1860) supposed that the new apical

end was formed by the septum on which new calcareous

material was deposited. Thus, the less convex shape of the

septum changed into the domelike form of the apex. Ac-

cording to him, the reconstruction was done by means of

two special and longer tentacles capable of massive and

precisely controlled secretion of calcareous material. He

substantiated their existence by the presence of a groove in

the median plane of the conical part of the shell, as well as

the presence of transversal grooves. Such a mode of shell

secretion is known in recent argonauts (Naef 1923, Hewitt

& Westermann 2003).

Blake (1882, p. 35) accepted Barrande’s conclusion

and wrote: “These features are best accounted for on the

supposition of Barrande, that the animal had the power of

breaking off the end of its shell at the septa, and of deposit-

ing shell matter on the truncated end. Of course this in-

volves the assumption that the animal could reach so far

outside the shell, which must have been therefore more

nearly internal than in the Nautilus.” Schröder (1888) ex-

plains the varying appearance of the apex in Sphooceras as

truncation in different portions of the shell, but he regards

Sphooceras as a close relative of Nautilus. Flower (1941)

remarked that the structures on adapical septal surfaces of

Sphooceras are open to very different interpretations. He

saw the most probable way to explain them as the surfaces

of hyposeptal deposits. He claims that the camerae have

evidently been broken at the point of greatest weakness,

namely in the region of the pseudoseptum. Movement of

the animal and surrounding water caused separation of

both parts of the shell. He offered no explanation for the

concentric markings bearing fingerprint patterns (Flower

1941, p. 473). Tasnády-Kubacska (1962, p. 69) expressed

an opinion that truncation of the last chambers in some

orthoceratid may have been due to resorptive processes,

activated by the siphuncle and the intracameral tissues and

isolating deciduous portions, which finally broke off.

However, the existence of truncation was challenged by

some authors (Dzik 1984, Doguzhaeva & Mutvei 1989). For

everyone involved in these discussions, the crucial point was

the mechanism of truncation. Dzik briefly discussed this

problem (1984, p. 135) in context with Sphooceras as well

as with the Ascoceratidae and concluded that “one cannot

suggest any reasonable mechanism of shell truncation”.

Doguzhaeva & Mutvei (1989) saw the problem of finding

conclusive evidence of truncation in Palaeozoic cephalo-

pods in their poor structural preservation.

Turek & Marek (1986) provided other evidence support-

ing truncation, especially through the documentation of the

ontogeny of the species. Sphooceras truncatum and closely

related species were later studied by Gnoli & Kiselev

(1994). According to the latter authors, the apical part was

symmetrically sealed by the cameral mantle after truncation

and the cameral mantle extended through siphonal opening

could have left the fingerprint pattern on the truncation sur-

face (comp. Gnoli & Kisselev 1994, p. 417).

In spite of the considerable attention Sphooceras re-

ceived there is no consensus concerning the existence of

periodic truncation and the mode of secretion of terminal

callus, nor is the systematic position of the genus

Sphooceras (e.g. Sweet 1964, Dzik 1984, Gnoli & Kisselev

1994, Zhuravleva & Doguzhayeva 2002, Kröger 2008).

Also questions concerning internal structures, the mode of

their secretion and the ecology of this species have not

been sufficiently answered. For these reasons, the species

Sphoceras truncatum has been revised, using both histori-

cal material and new discoveries. Preliminary report sum-

marising main results of this research was published by

Turek (2007).

Other cephalopods morphologically similar to Sphoo-

ceras truncatum have been taxonomically revised. “Ortho-

ceras”sarcinatum Barrande, 1868 is newly assigned to this

species. Median sections of five well preserved specimens

of “O”. disjunctum Barrande, 1868 allowed detailed study

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Bulletin of Geosciences  Vol. 87, 4, 2012

of their internal structure and discussion of the systematic

position. The existence of an apical thickening (callus), not

documented previously for this species, indicates it be-

longs in the genus Sphooceras. Muscle scars are also de-

scribed here for the first time, and its stratigraphic range is

refined.

Additional evidence for periodic truncation of the shell

in the Silurian cephalopod Sphooceras and the discovery of

a colour pattern on the “new” apex in S. truncatum are

equally exceptional and of great importance. These fea-

tures represent proofs for the temporary encasing of the

whole shell of this cephalopod by soft tissue. Additionally,

this evoked the question concerning systematic position of

Sphooceras and some other closely related cephalopods

with an orthoceracone shell. Similarity to coleoids is fur-

ther emphasized by the very short phragmocone and a

smooth or indistinctly sculptured shell surface. Sphooceras

probably possessed a minute spherical initial chamber

(protoconch), which is another specific character of

endocochleate cephalopods and also of orthocerids, early

ammonoids and bactritoids. This generic study brings ad-

ditional support for separation of orthoceracone cephalo-

pods with small spherical protoconch lacking a cicatrix

from the nautiloids.

Material and methods

Most of the available specimens of Sphooceras truncatum

have been collected in the Prague Synform (Bohemia,

Czech Republic) during 19th century. More than 500 speci-

mens come from Barrande’s collection; about 20 revised

specimens are deposited in the collection of M. Shary.

These specimens come from the classic localities “Hinter

Kopanina” (several collecting sites near Zadní Kopanina,

e.g., Draská Gorge section, early Ludfordian), Butowitz

(Praha-Butovice: Na břekvici and Kovářovic mez sections;

earlier Ludlow and early Ludfordian), Wohrada (Mušlovka

Quarry near Praha-Řeporyje), Wiskočilka (Praha-Malá

Chuchle, Vyskočilka Hillside; early and middle Ludlow),

Kosorz (Praha-Kosoř; late Ludlow) and Lochkov (several

localities south of Lochkov Village, Ludfordian). The

exact stratigraphic position and collecting site of speci-

mens from old collections is often uncertain, except for lo-

calities with a characteristic mode of preservation (Buto-

vice – Na břekvici, Zadní Kopanina – Draská Gorge). More

than 200 specimens have been collected during the last two

decades by the authors, Ladislav Zedník and Antonín Čí-

žek. These specimens come mostly from measured and

numbered reference sections with a high biostratigraphical

resolution, permitting dating into specific graptolite biozo-

nes. Many specimens have been found in new localities,

which allows the more acurate description of distribution

patterns, ranges and abundances of Sphooceras. Jiří Kříž

assembled an extensive collection containing 136 speci-

mens, collected from the Homerian cephalopod limestones

in the Arethusina Gorge section near Praha-Řeporyje. Spe-

cimens used in this study are usually not deformed; some

are almost complete. Apical parts of phragmocones pos-

sessing three to five phragmocone chambers and probably

representing deciduous parts of shells occur abundantly.

The study of S. disjunctum is based primarily on mate-

rial from Barrande’s collection. Around 40 specimens

come from Butowiz (Praha-Butovice: Na břekvici, earlier

Ludlow). The species was newly found in Praha-Butovice,

Kační Quarry, late Wenlock, Praha-Malá Chuchle, Vysko-

čilka Hillside and Praha-Řeporyje (early Ludlow). Speci-

mens are undeformed, with preserved internal structures,

usually with the first phragmocone chamber missing.

To gather additional information about the internal

structure of the shell, 38 specimens of Sphooceras trun-

catum and five specimens of S. disjunctum were cut in the

median plane. Unfortunately, due to recrystallization and

infilling of the phragmocone by sparitic calcite, internal

structures are frequently completely destroyed. Neverthe-

less, about 25 specimens, primarily from the Praha-

Butovice and Kosoř localities, are very well preserved in-

ternally, so characteristic features could be studied. Speci-

mens were photographed with an Olympus Camedia 5050

digital camera, minute shells and details with an Olympus

DP 700 digital camera attached to an Olympus SZX 12 mi-

croscope. Some polished sections were documented by

scanner. To obtain better contrast, a specimen with a pre-

served colour pattern and median sections were photo-

graphed immersed in alcohol. Other specimens were

coated in ammonium chloride prior being photographed.

The resulting images were processed using Photo Paint

software.

The basic morphological terminology is according to

Teichert (1964). Due to some unique morphological fea-

tures of Sphooceras, a schematic drawing is attached

(Fig. 1); some terms used in this paper are explained in the

chapter dealing with its morphology. Since the truncation

process removes chambers, the most apical remaining

chamber of the phragmocone (possessing the callus) is

called the first.

Studied specimens are deposited in the Palaeonto-

logical collection of the National Museum, Prague (prefix

NM L) and in the collection of the Geological Survey,

Prague (prefix CGS SM). Some specimens from the Silu-

rian of Central Bohemia, which significantly contributed to

our knowledge about this species, are deposited in Shary’s

collection, Museum of Comparative Zoology, Harvard

(prefix MCZ), Natural History Museum, London (prefix

NHM) and Naturhistoriska Riksmuseet,Stockholm (prefix

RM Mo). The Stockholm collection includes a few Bohe-

mian specimens and four specimens from the Silurian

rocks of Gotland, Sweden.

769

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Morphology of Sphooceras

Barrande (1860, 1868) described “Orthoceras”truncatum

in detail, including shell structures and the process of trun-

cation. Special attention has been paid here only to features

not mentioned by J. Barrande or to features having special

importance for the systematic assignment of Sphooceras

within the Cephalopoda and for palaeobiological interpre-

tations.

Variability

Our study of the intraspecific variability of Sphooceras

truncatum is based primarily on specimens collected by us

at the Draská Gorge section near Zadní Kopanina. About

200 non-deformed specimens of this species, both fragments

as well as “complete” shells, come from a 20 cm thick bed

of yellow-grey strongly weathered dolomitic cephalopod

limestone, that corresponds with the late S. linearis Zone

770

Figure 1. Schematic drawing of Sphoo-

ceras explaining terminology used in this

paper.•A–adult specimen with partially

removed shell.•B–apical region and ad-

jacent part of phragmocone, showing ex-

ternal and internal features of shell. Based

on specimen illustrated in Fig. 20.

Abreviations: a – aperture, ac – apical cal-

lus formed by episeptal cameral deposits

fused with septum, ae – annular elevation,

bc – body chamber, cr – connecting ring,

dz – detachment zone, ed – episeptal de-

posits, fl – finger-pattern layer, fc1 – first

phragmocone chamber, fc1f – empty

space of first phragmocone chamber filled

with sparitic calcite, fc2 – second phrag-

mocone chamber, gl – growth lines,

hd – hyposeptal deposits, iw – invagi-

nation of wrinkles, lt - line of truncation,

ol – outer shell layer, osw – outer shell

wall, p – plug, r – radial sculpture on sur-

face of cameral deposits (below partially

removed wrinkle pattern layer), s – suture,

sn – septal neck, sp – septum, vt – replica

of vascular tissue on concave surface of

cameral deposits (seen on calcite camera

filling), vts – vascular tissue impression

on convex surface of septum. Not in scale.

Figure 2. Sphooceras truncatum, Ludlow, Kopanina Formation. • A–E – specimen MCZ 160328, locality Kosoř, specimen with preserved colour pat-

tern in apical part of shell. A – apical view; B, C – detail of apical part of shell; oblique and lateral views; D, E – lateral views. • F, G – almost complete

adult specimens with preserved apertural margin; F – specimen NM L 40959, Praha-Butovice; G – specimen NM L 9201 illustrated by Barrande (1868,

pl. 343, fig. 17), Zmrzlík.•H–specimen NM L 9180 illustrated by Barrande (1868, pl. 343, figs 1–5), Zmrzlík; apical part of shell; imprint of soft tissue

on concave surface of cameral deposits preserved on sparitic infilling of first chamber; dark colour is probably owing to primarily high content of organic

matter in cameral deposits, × 1.3. • I – specimen NM L 9193 illustrated by Barrande (1868, pl. 343, figs 1–3), Zadní Kopanina; apical part with partly ex-

foliated layer with finger-print pattern; surface of cameral deposits having radial structure is exposed; lateral view, × 1.7. • J, O – specimen NM L 9197 il-

lustrated by Barrande (1868, pl. 342, figs 11–13), Zadní Kopanina; apical view (× 1.7) and detail of the border area between cameral deposits and shell,

×10.•K–specimen NM L 40960, Kosoř; almost complete adult growth stage.•L–specimen NM L 9190 illustrated by Barrande (1868, pl. 342, fig. 9),

Kosoř; almost complete internal mould with only four phragmocone chambers; cameral deposits in apical region slightly developed. • M, N – lectotype

NM L 9184, illustrated by Barrande (1868, fig. 15, and 1868, pl. 341, figs 15–18), Praha-Butovice; the first phragmocone chamber showing finger-print

pattern and sudden change in course of roughly concentric ridges (invagination), × 0.9. Scale bar: 30 mm, details with magnification.

Bulletin of Geosciences  Vol. 87, 4, 2012

771

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

(early Ludfordian, S. linearis Zone, former “Cromus beau-

monti trilobite horizon”). Different growth stages include

specimens possessing a dorsoventral diameter of 2 to

30 mm (measured in the position of the first septum). This

collection made a study of its variability within palaeopo-

pulations across several depositional cycles possible.

S. truncatum collected from other localities exhibits a

similar pattern of size classes. Specimens with large cross-

sections are rare and come from the localities Praha-Bu-

tovice and Praha-Braník. Six were collected in Praha-

Butovice: Na břekvici, Neodiversograptus nilssoni Zone,

earlier Ludlow. They comprise isolated first phragmocone

chambers, considerably infilled by cameral deposits. Three

are almost the same size and attain a dorsoventral length of

approximately 80 mm, the other three have dorsoventral

diameters of 65, 49 and 48 mm. A recently found specimen

from Praha-Braník (NM L 40919) has 80 mm diameter.

However, it is much more complete, comprising the

phragmocone and the adapical part of the body chamber.

The eight-chamber phragmocone is about 110 mm long, its

estimated total length is 270 mm. This specimen, preserved

as a limestone nodule in shale was found about four meters

below the cephalopod limestone bank in Školní vrch sec-

tion (Praha-Braník); its exact age is unknown, but a co-oc-

curring Saetograptus fritschi, a graptolite indicates

L. scanicus or S. linearis Zone (Gorstian, early Ludlow).

All large specimens are slightly stratigraphically older than

specimens from the Zadní Kopanina locality.

Although the finger shape of the shell in Sphooceras

truncatum is striking and characteristic, the shell may be

slender and relatively long, or wider and shorter (Table 1,

Fig. 2). In the pre-adult growth stage, both dorsoventral

772

Table 1. Measurements of complete specimens of Sphooceras truncatum in mm. * Measured at the boundary phragmocene/body chamber.

Specimen Sagital

lenght Body chamber

lenght Phragmocone

lenght Dorsoventral

diameter * Width Dorsoventral

diameter max Dorsoventral diameter

at aperture Ratio bl/f l Ratio dv/w

L 9201 112 62 50 24 22 26 23 1.2 1.1

L 9202 100 55 45 19 19 20 19 1.2 1.0

L 9180 130 74 56 33 31 35 33 1.3 1.1

L 9182 111 67 44 27 25 30 28 1.5 1.1

L 9185 86 52 34 25 22 26 25 1.5 1.1

L 17534 110 65 45 28 24 30 32 1.4 1.2

L 9191 140 77 63 30 28 30 30 1.2 1.1

L 9190 127 78 49 35 33 36 34 1.6 1.1

L 9186 76 44 32 25 22 26 26 1.4 1.1

L 9189 55 34 21 18 17 19 18 1.6 1.1

L 17533 82 46 36 20 19 23 23 1.3 1.1

L 9197 104 60 44 21 19 23 22 1.4 1.1

L 21467 78 44 34 17 16 20 20 1.3 1.1

L 9203 71 45 26 15 15 16 16 1.7 1.0

L 9183 92 55 37 19 19 24 24 1.5 1.0

L 41333 110 65 45 34 30 ? 33 1.4 1.1

L 40960 143 78 65 41 39 43 40 1.2 1.1

L 40959 89 51 38 22 20 24 22 1.3 1.1

L 41334 95 56 39 30 30 32 30 1.4 1.0

L 41336 111 61 50 26 25 28 28 1.2 1.0

L 41337 95 55 40 25 22 28 24 1.4 1.1

L 40940 95 55 40 24 18 24 23 1.4 1.3

L 41335 125 75 50 31 29 33 32 1.5 1.1

L 41339 136 83 53 31 27 31 30 1.6 1.1

L 41338 101 61 40 25 23 26 24 1.5 1.1

L 40919 288 148 140 90 86 ? ? – 1.0

35050 119 75 44 22 22 23 22 – –

L 40919 288 173 115 90 86 – – – –

L 42163 24 15 10 6 4.1 7 7 – –

L 40940 95 60 35 23 18 24 23 1.7 –

Bulletin of Geosciences  Vol. 87, 4, 2012

and lateral diameters frequently decrease, so that fully

grown specimens show the maximum diameter in cross

section is about midway through the last body chamber. In

several internal moulds, a moderate constriction of the

peristome is present. This shape of the shell, strongly short-

ened last or last two phragmocone chambers and heavily

developed cameral deposits almost completely filling the

first chamber are features considered to be indicators of

the mature growth stage. Size variability of fully-grown

specimens is extraordinary. Such variability in fully-grown

longicone cephalopods was not previously known, al-

though it had been commonly recorded in nautiloids (see

discussion in Stridsberg 1985, Manda 2008, Manda &

Turek 2011).

The cross section of the shell is subcircular or widely

elliptic, with the dorsoventral diameter being larger than

lateral. The aperture is oblique to the shell axis; the

hyponomic sinus is shallow and broad. A shallow ocular si-

nus is present in some specimens. Both size and vaulting of

the first phragmocone chamber are highly variable: short to

long; moderately convex to highly vaulted, in some speci-

mens almost pointed. Convexity of septa during ontogeny

generally decreases. The last two or three septa in

fully-grown specimens are very closely spaced (Fig. 3F, G,

Table 2, App. 1, 2). The outer shell wall and septa are thin,

the septa pass into markedly thickened orthochoanic to

suborthochoanic septal necks. The shape of the slightly

ventrally shifted siphuncle is not known, as only septal

necks are preserved. Based on the presence of subortho-

choanitic septal necks, moderately inflated connecting

rings appear probable (Dzik 1984). Because no complete

siphuncular segment has ever been found, their fully or-

ganic nature is assumed. In one specimen of Sphooceras

truncatum, some traces in the form of secondary calcite

lining are discernible, suggesting the lost connecting rings.

The position of two graptolite rhabdosomes of

Saetograptus fritschi within these traces (NM L 40919,

Fig. 4) indicates that they were originally deposited within

the siphuncle. The presumed connecting ring traces are

slightly inflated within the phragmocone chambers; the

substantially smaller diameter of the traces, compared with

the diameter of septal necks, is interpreted as a result of

post-mortem processes.

The surface of the shell is usually smooth or bears very

fine, widely spaced growth lines; between these, even finer

closely spaced growth lines may be discernible. In a few

specimens, growth lines are rather distinct. Their course is

laterally oblique to the shell axis; dorsally they form a shal-

low adapically convex saddle and ventrally a shallow and

broad sinus. Some of the stratigraphically youngest speci-

mens from the uppermost part of the Kopanina Formation

(latest Ludfordian and earlier Přídolí) show more pro-

nounced and densely spaced growth lines and a slightly

larger apical angle (Fig. 5A, I). Transitional forms between

these two morphotypes have been found. The great differ-

ences in surface patterns on the first chamber among indi-

vidual specimens are the result of different factors con-

nected with the process of truncation (see section dealing

with truncation).

An interesting anomaly concerning shell size is that of

palaeopopulations containing specimens with only small

shells, found in the narrow stratigraphic level of the latest

Neocuculograptus kozlowskii Zone (Ludfordian, Ludlow).

This level corresponds with the onset of the Kozlowskii

and Lau extinction event (Urbanek 1993, Calner 2008,

Manda et al. 2012). Three paleopopulations were exam-

ined, from three thin beds with erosive surfaces, each rep-

resenting a single depositional event: Zadní Kopanina –

Nad Jirasovým lomem, bed No. 3, maximum dorsoventral

diameter 14 mm; Koněprusy – Cesta section, bed No. 5,

773

Table 2. Phragmocone chamber lengths in Sphooceras truncatum and

Sphooceras disjunctum in mm.

Phragmocone chamber (from truncation) and presence

of body chamber (bc)

Specimen 1th 2th 3th 4th 5th 6th 7th

Sphooceras truncatum

L 40935 3.2 2.5 2.7 2 2 bc

L 40940 66863.42.5bc

L 40939 5.5 8 6 5

L 40930 3.3 6 4.5 4.5 4.3 2.3

L 40931 7.5 2.5 6 6 6.5 2.5 bc

L 9199 12.5 8 7.1 5.8 5.8 7.4

L 42164 4 7 8.5 8 5

L 40929 9777666bc

L 40928 9 8.8 6.3 7 6.1 4.9 bc

L 40925 7.8 7.6 6.1 6.6 4.7 bc

L 40927 10.3 8.2 6.2 7.3 5.8

L 40926 9 8.1 5.6 5.7 6.5 4.8

L 40932 11.8 9.5 9.5 9.5 9.5 5.2

L 40933 10.3 9.2 6.3 6.6 6.1 6.1 3 bc

L 40919 17 16.5 16.2 14.8 16

MCZ 160432 9.5 9.5 7 7 5.3 5 3 bc

MCZ 160212 5.2 8.7 6 4.3 bc

Mo 42807 6.2 6.8 8 6 6.2 6 2.5 2.5 bc

Mo 42808 4 5.8 6.3 6.4

Mo 42813 2.7 4.5 3.7 4 bc

Sphooceras disjunctum

L 40937 2.6 5.3 5.2 3.2 bc

L 40938 2.1 4.9 4.5 3 bc

L 40936 1.2 1.8

L 40944 ? 8.5 6 5

L 17550 ? 3.5 3.5 2.8 bc

L 41313 1.7 2.8 2.3 2.3 bc

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

maximum dorsoventral diameter 9 mm; Nová Ves – Hra-

diště II section, bed No. 13, maximum dorsoventral diame-

ter 10 mm. Most specimens had a much smaller dorsoventral

diameter, i.e. 5–8 mm. The largest shell from these beds,

14 mm diameter, is markedly smaller than those in the un-

derlying strata. Above this small-shelled population, a Laza-

rus gap occurs, then Sphooceras truncatum reappears in the

latest P. latilobus-Sl. balticus Zone. The appearance of the

palaeopopulation with small shells corresponds to the begin-

ning of shallowing, increasing anoxia and instability of cur-

rents in the Silurian sea (Manda & Kříž 2006). The decrease

in shell size (Lilliput effect) may be related to these harsh

conditions (see Harries & Knor 2010).

In general, the intraspecific variability of Sphooceras

truncatum, the sole well-known species of the Sphoo-

ceratidae is quite high (Fig. 6, App. 1, 2). Although the spe-

cies ranges from the Wenlock to the earlier Přídolí, i.e.

more than 8 Ma, neither a clear evolutionary trend nor

changes in variability were traced.

A smaller species of Sphooceras –S. disjunctum –is

fairly uniform, both in size and morphology. Specimens

from Praha-Butovice, Na břekvici, Neodiversograptus

nilssoni Zone, earlier Ludlow are perhaps from one palaeo-

population. Two other localities, Praha-Butovice, Kační

Quarry, C. lundgreni Zone, T. testis Subzone and Praha-

Malá Chuchle, Vyskočilka Hillside, L. scanicus Zone have

yielded palaeopopulations with smaller shells. Lengths of

shells from these three localities vary from 32 to 45 mm;

dorsoventral diameter from 13 to 18 mm. There are 3 to 5

chambers in the phragmocones. Most internal moulds have

a visible constriction of the peristome, which corresponds

to a thickening of the external shell wall (Fig. 7B, C). Con-

sequently, they are quite probably shells of adults. The

shell wall near the aperture is unusually thin (0.2 mm).

Thin deposits forming the apical callus correspond to very

short phragmocones. They are similar to deposits in

Sphooceras truncatum with similar phragmocone lengths.

Short siphonal necks are suborthochoanitic or cyrto-

choanitic, sometimes even both in the same specimen.

Slightly asymmetrical septa are only moderately convex;

marked differences in convexity were not observed.

Muscle scars

Dorsomyarian position of muscle scars, typical for ortho-

cerids (Sweet 1957, Mutvei 2002a) has been ascertained in

both studied species of Sphooceras. The annular elevation,

found only in adult Sphooceras truncatum specimens, is

very faint. It is located in the basal part of the body cham-

ber, close to the last septum, forming a narrow stripe ven-

trally and ventrolaterally, becoming one distinct lobe on

the dorsal side (Fig. 5G, H, J, K). A complete dorsal muscle

imprint was observed in only one specimen. Several other

specimens show a fine annular elevation only ventrally and

laterally. A similar shape of the retractor muscle imprints is

visible in one specimen of S. disjunctum (NM L 40976,

Fig. 8C, D). The border of the adapical annular elevation

indicates that the lobe was created by two retractor attach-

ments merging. Small retractor muscle scars indicate rela-

tively underdeveloped retractor muscles. From that, it may

be concluded for active movement that the animal relied on

its tubular hyponome musculature.

Detachment zone

The annular stripe, frequently present adapically on the ou-

ter surface of the shell, roughly above the mural part of

the first septum is here named the detachment zone

(Fig. 5B–E). It is the area where, during truncation, the mu-

ral part of the septum usually detached from the remaining

part of the shell. There is often a visible step in shell diame-

ter at the adapertural edge of the detachment zone. The ada-

pical edge frequently has a shallow indentation, bordering

the cameral deposits in the apex, which reach surface of

the shell; they are different from the outer shell wall, in

structure and sometimes in colour. While the shell wall is

smooth and usually light gray, the apical callus deposits

has longitudinal striations or dimples and is dark. The ada-

pertural edge of this zone is the actual detachment boun-

dary (line of truncation). Growth striations cover the rema-

ining shell surface forward to the aperture. As long as the

shell surface is not completely smooth, the striations do not

774

Figure 3. Sphooceras truncatum (Barrande, 1868). Ludlow, Kopanina Formation. Specimens sectioned in median plane.•A–NML40932, Zadní

Kopanina; domelike first chamber with strongly developed cameral deposits ventrally, × 1.3; see also Fig. 14A. • B – specimen NM L 9199 illustrated by

Barrande (1868, pl. 343, fig. 15), Praha-Lochkov; dome like first chamber with moderately developed cameral deposits showing their unusual growth in

central part of apical region, × 1.2.•C–NML40925a, vicinity of Prague; marked shortening of phragmocone chambers during growth. Thick deposits

ventrally, × 1.5; see also Fig. 14F. • D, N – specimen NM L 40929a, vicinity of Prague; third phragmocone chamber with episeptal deposits interpreted as

possible initial stage of apical callus, × 1.6; detail of the chamber with episeptal deposits, × 4.1 (see also Fig. 9B).•E–NML40939a, vicinity of Prague;

detail of apex showing infilling of siphonal opening forming the plug, × 2.3.•F–specimen MCZ 160432, Kosoř; progressive shortening of phragmocone

chambers. 5th chamber filled with episeptal and hyposeptal deposits, × 1 (see also Figs 9D and 14H). • G – specimen NM L 40933a, Praha-Slivenec; pro-

gressive shortening of phragmocone chambers, × 1.2.•H–specimen MCZ 160212, Praha-Slivenec; growth stage early after truncation with very thin

cameral deposits, × 0.9. • I–L – specimen NM L 40924a, Zadní Kopanina; strongly developed cameral deposits with radial lamellae (comp. also Fig. 9A);

I × 1.2; J – the same specimen; detail of cameral deposits in dorsal part of shell, × 7.5; K, L – apical part; details (× 2.1 and 4.6).•M–specimen illustrated

here in Fig. 3B, × 2.5.

Bulletin of Geosciences  Vol. 87, 4, 2012

775

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

cross this boundary. The line of truncation abruptly dis-

rupts the outer shell wall, as is clearly documented by the

course of growth lines.

Cameral deposits

Only a few cephalopod workers have mentioned the came-

ral deposits in Sphooceras (Flower 1941, Dzik 1984, and

recently Kröger 2008). Other authors (e.g. Sweet 1964, Ki-

selev 1993, Gnoli & Kiselev 1994) evidently distinguished

in terminology the callus and cameral deposits and they

characterised this genus as a nautiloid without cameral de-

posits. However, the callus in Sphooceras represents only

a specific form of cameral deposits (probably fused

with truncation septum) forming an apical part of the shell

immediately after truncation, before secreting additional

layers on its surface.

Cameral deposits forming the main body of the apical

end of the shell (callus) represent a feature invariably oc-

curring in all specimens studied. Their development (thick-

ness of the callus) depends on the length of the phrag-

mocone. Longer phragmocones possess thicker episeptal

deposits while in shorter shells (with three or four

phragmocone chambers, i.e. growth stages just after trun-

cation) deposits forming the “callus” are very thin. In large,

fully-grown specimens the deposits may occupy almost the

whole volume of the first phragmocone chamber (Figs 3K,

4A, 9A, 10). The synchronous increase in callus thickness

and in the number of chambers between body chamber and

callus suggests an ongoing growth of the callus subsequent

to truncation. The presence of the apical callus probably

represented some kind of counterweight probably enabling

the animal to keep its shell horizontal.

In specimens with slightly developed deposits, apical

callus reach its maximum thickness around the sealed

septal foramen (Figs 3H, 9C, E, 11A, D). Laterally, their

thickness decreases more or less regularly. A crater-like

depression in the convex side of the apical callus within the

confines of the plugged septal foramen is frequently pres-

ent; in medially cut specimens a trace of a very narrow

channel in the septal foramen plug is sometimes discern-

ible. In some specimens the colour and structure of the ma-

trix infilling the septal foramen differs from neighbouring

cameral deposits forming the callus (Figs 3D, G, 9B, E,

11A, D). In specimens with a longer phragmocone,

cameral deposits are more developed ventrally. The central

part of the callus is sometimes markedly thinner. This fea-

ture is very well seen in median sections as well as on some

of Barrande’s type specimens, in which infilling only of the

empty space of the first chamber is preserved, so that a cast

of the adapertural surface of the callus is exhibited. The

callus is sometimes darker, due to the presence of organic

matter. It may be a consequence of an originally high con-

tent of organic matter. The radial structure of the deposits is

clearly visible close to the outer surface of the shell in

well-preserved, medially cut specimens. Sometimes the

structure is accentuated by pyrite or Fe-hydroxide. The de-

posits comprise lamellae or thin pillars interconnected

through lateral anastomoses (Dzik 1984), sometimes ar-

ranged in rows, so that the outer surface looks like a pitting

or fine longitudinal ribs. However, one large and strongly

weathered specimen (NM L 40922) of Sphooceras shows a

spongy character of these deposits. Their microstructure

thus seems to be analogous to that observed in the cameral

deposits of lamellorthocerids such as, e.g. Arthrophyllum

Beyrich, 1850 (for summary see Zhuravleva & Dogu-

zhayeva 2002). In specimens with massively developed

deposits, their microstructure changes rapidly inward; their

lamellar character disappears and becomes sparitic calcite.

These specimens also exhibit slightly developed deposits

on the convex surface of the first septum, documenting pre-

cipitation of calcium carbonate on the outer surface of the

siphonal neck (Fig. 10A, B).

The fact that this material was deposited by the living

animal is evident partly from the patterns of deposition and

its characteristic structure resembling the radially arranged

calcite prisms of belemnite rostra. Additionally, in a certain

phase of ontogeny (just after truncation) it formed the only

wall at the apical end of the shell. Its development and ar-

rangement indicates that it also served to keep the shell

horizontal.

Besides the apical callus, cameral deposits interpreted

as a live-secreted structure have been found in three speci-

mens of Sphooceras. The 4th phragmocone chamber of

S. truncatum (specimen NM L 40929a, Figs 3D, N, 9B)

shows episeptal deposits lining the concave part of the sep-

tum. Their development and fusion with structuraly changed

septum is presumed to be a condition preceding truncation.

This hypothesis is based primarily on the specimen of

S. disjunctum (NM L 41032, Figs 12B–D, 13A, D, E).

While the average thickness of the free parts of the septa

(measured in the mid point between outer shell wall and

siphonal opening) is 0.9 mm, thickness of the septum fused

with cameral deposits in the ventral sector (measured in the

mid point between the ventral side and siphonal opening) is

4.4 mm. The ventral part of this “septum” is formed by

white-grey sparitic calcite; only the convex surface of the

septum is coloured by darker pigment. Dorsally from the

siphonal opening, the septum fused with cameral deposits

is markedly thinner (near the axis of the shell its thickness

is 2.7 mm). Further dorsally it narrows, and finally its

thickness is almost the same as the thickness of neighbour-

ing septa. In one quarter of the distance between the ventral

side and the septal foramen, a honey-coloured lamella ap-

pears on the concave side of the septum, gradually thicken-

ing medially and near axis of the shell, becoming the total

thickness of this compound septum/deposit structure.

776

Bulletin of Geosciences  Vol. 87, 4, 2012

These deposits do not substantially reduce the volume of

the septal foramen. If this compound structure later formed

the apical callus, secretion of a plug closing the siphuncle

and perhaps one another septum was the next step in prepa-

ration for truncation.

As cameral deposits inside the phragmocone have been

found in two cases only, their secretion shortly before trun-

cation is hypothesized. In one adult specimen (MCZ

160432; see Figs 3F, 9D, 14H) both episeptal and hypo-

septal deposits are developed. They are present in the 5th

phragmocone chamber, i.e. close to the animal’s centre of

gravity. The previous and following chambers are empty

except for the apical callus. Their morphology indicates

that they were not related to the truncation process. They

probably appeared in fully-grown specimens reducing its

positive buoyancy. It also means that occasionally, typical

777

Figure 4. Sphooceras truncatum (Barrande, 1860); specimen NM L 40919a; Ludlow, latest Gorstian or earlier Ludfordian, Praha-Braník, Školní vrch,

Kopanina Formation. • A –incomplete adult growth stage cut in median plane. Two last phragmocone chambers and adjacent part of body chamber not il-

lustrated. The first chamber almost completely filled with cameral deposits showing radial structure in their outer part with graptolites Saetograptus

fritschi within the siphuncle segment of third chamber, × 1.6. • B – the same specimen; detail of the outer shell wall; arrows indicate the place of truncation

and (?)traces of a connecting ring, × 3.8.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

cameral deposits may appear inside the phragmocone

chamber.

Thickening of the apical part of the shell in S. dis-

junctum corresponds to initial stages of the apical callus in

S. truncatum. The phragmocone of S. disjunctum has no

more than five chambers and the chambers are very short.

To maintain neutral buoyancy, the shell is more delicate

with a very thin apical callus.

Plug closing septal foramen

The plug closing the septal foramen shows a structure

slightly differing from the surrounding cameral deposits.

The convex surface of the callus corresponds to the convex

part of the structurally reworked septum and the sealed sep-

tal foramen is clearly visible. In well-preserved specimens,

concentric and fine radial structures can be seen on the outer

surface of the plug. The outer margin bordering the plug

usually forms a grove and the central part of the plug is fre-

quently slightly submerged. In the very centre of the plug, a

crater-like depression is usually present, with 1/5 to 1/6 of

the diameter of the siphonal opening (Figs 9B, C, E, 12 A,

15B, M). The outermost smooth layer deposited around the

plug either only borders the plug, or either partly or com-

pletely overlays the fingerprint-pattern layer. In former

case, the boundary between the smooth layer and the

fingerprint-pattern layer is sharp (Figs 15B, 16B). Diffe-

rent material and different outer morphology of the plug in-

dicates that the plug was formed by tissue entering the sip-

honal opening from the inside of the first chamber. The

sharp border between the plug and outer layers covering

the callus excludes the possibility that this layer was for-

med by cameral mantle extended through the siphonal

opening. Also, the necessity of sealing the siphonal ope-

ning before truncation would have prevented repairs to de-

tachment zone by cameral mantle (comp. Gnoli & Kiselev

1994). Successive phases of closing of the septal foramen,

from initial narrowing of the tube to a completed plug can

be traced in various medially sectioned specimens. In one

medially cut specimen of S. disjunctum (NM L 40938,

Fig. 7A, G, H), the siphonal opening in the first septum ap-

pears plugged but there are no traces of any episeptal depo-

sits, formation of which very probably preceeded forma-

tion of the plug. Therefore, it seems more probable that the

siphonal opening in the first septum did not lie exactly in

the medium plane, and the brownish colour of the “plug” is

in fact the wall of the siphonal neck.

Deciduous part of phragmocone

One argument against periodic truncation in Sphooceras

was the alleged absence of deciduous parts of the shell in

the fossil record (Teichert 1964, Dzik 1984, Kröger 2008),

but claims of this absence are based solely on Barrande’s

earliest writings (Barrande 1860). Later, in 1877, he men-

tioned that his collection contained such parts of cephalopod

shells. During our fieldwork, we have found that speci-

mens of Sphooceras truncatum having three to five cham-

bers but lacking the body chamber are quite common (e.g.

Barrande 1868, pl. 343, figs 4, 5; Figs 15D, I, L, 16I and

17E herein). The absence of body chambers was not due to

separation from the phragmocone during collecting – they

were already missing in the sediment. S. disjunctum is less

abundant and only a few specimens have been obtained du-

ring recent field works. Isolated apical parts of phragmoco-

nes coming from old collections do not exclude the possibi-

lity that remaining part was lost during excavation.

Therefore, existence of phragmocone parts in S. truncatum

is further evidence confirming the truncation process in

Sphooceras.

Colour pattern and its significance

for the determination of the life orientation

of the shell

The colour pattern in Sphooceras has been found so far in

only one specimen (MCZ 160328, Fig. 2A–E) from

the “Kosoř” locality (Ludfordian, Kopanina Formation),

and it is especially important for tracing the process of

778

Figure 5. A–Sphooceras sp., specimen NM L 40976, Ludlow, Ludfordian, Pristiograptus fragmentalis Zone, Praha-Lochkov, Nad ubikacemi,

Kopanina Formation; adapical part of the shell with densely spaced growth lines; lateral view, × 2.8. • B–N – Sphooceras truncatum (Barrande, 1860),

Ludlow, Kopanina Formation.•B–specimen NM L 00008, Zadní Kopanina; adapical part of the shell with well seen finger-print pattern layer, detach-

ment zone and abruptly finishing growth lines; ventrolateral view; × 3.2. • C, D, E – specimen NM L 42165, Zadní Kopanina; incomplete shell showing

detachment zone – dorsal, ventral and lateral views, C, D × 1.4, E × 1.9. • F – specimen NM L 9194, illustrated by Barrande (1868, pl. 343, figs 4, 5), Zadní

Kopanina; apical view with smooth layer around the plug indicating secretion of this layer from plugged siphonal opening abapically, × 1.9.

• G, H, J, K – basal part of body chamber; internal mould showing single lobe of retractor muscles. • G, H – specimen NM L 40977, dorsal and dorsolateral

views, × 1.6. • J, K – specimen NM L 40958, Řeporyje – Mušlovka Quarry, dorsolateral and dorsal views, × 1.3.•I–specimen NM L 21467 illustrated by

Barrande (1870, pl. 448, figs 3–5), Slivenec, valley; “naked” apical part, detachment zone and well preserved surface sculpture, × 2.3. • L, N – specimen

NM L 9193 illustrated by Barrande (1868, pl. 343, figs 1–3), Zadní Kopanina, anomalous shell growth (healed sublethal injury); notice also two small

V-shaped damages adaperturally, L × 1.6,N×3.2.•M–specimen NM L 40980, vicinity of Prague; part of the shell with strongly vaulted apical part and

very narrow detachment zone, indicated by arrow, × 1.8.

Bulletin of Geosciences  Vol. 87, 4, 2012

779

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

truncation. The colour pattern is present in the apical re-

gion of the shell. The incomplete specimen has six phrag-

mocone chambers and an adjoined part of the body chamber.

The shell is exfoliated, except for the apical part; relicts of

the adjacent phragmocone chamber shell are preserved.

The body chamber is moderately deformed; its adapertural

part is secondarily dislocated, damaged, and partly filled

with grey matrix.

The colour pattern is characterised by stripes extend-

ing radially from the circumference of the plugged

siphonal opening, but they are only present on the dorsal

half of the shell. The stripes widen adaperturally and

fuse dorsally into an undivided brownish-grey area. Fol-

lowing the expansion of the apical part of the shell, new

stripes were inserted laterally. A bright-brown longitu-

dinal stripe is developed in the middle of the right side.

The light-grey area between this and the adjacent stripe

is about twice as wide as the stripes. Moving dorsally,

there are stripes that are progressively less discernible,

owing to the darker colour of the shell. The ventral half

of the shell is uncoloured. Shell relicts preserved in the

adjacent part of the phragmocone show no colour pat-

tern, and the border between the coloured and uncol-

oured part of the shell is sharply delimited by a darker

brownish belt along the first suture. This pigmentation

also continues on the ventral side, where it is of second-

ary origin.

The original colouration of the apical region was per-

haps bright, because the preserved stripes are well devel-

oped and because in colour preservation, remains of the

dark pigment are usually preserved. Explaining the sudden

diminishing of longitudinal stripes on the dorsal side in the

adapertural direction is more difficult. It can imply that the

colour pattern here was weakly expressed and disappeared

post-mortem. A camouflage effect serving for protection

of the animal could be provided by pigmentation of the soft

tissue covering the shell but why should there be a colour

pattern when the mantle still covered the shell? In order for

the colour pattern to serve as camouflage, this part of the

mantle might have been (i) speculatively translucent,

(ii) retracted at one point, thus exposing the colour pattern

or (iii) moved back and forth across the shell, depositing

additional shell layers as in cypraeid gastropods. Owing to

the periodic truncation, a short phragmocone was main-

tained during the entire ontogeny. It possibly enabled re-

peated complete covering of the shell by mantle extension,

after each truncation. A similar model of mantle extension

has been described for some Palaeozic (Korn 2000) and

some Mesozoic ammonoids (Drushchits et al. 1978). The

evidence for such behaviour is derived from secondary ex-

ternal shell layers and sometimes from healed shell injuries

(Kröger 2002).

It is interesting to compare the colour pattern on the

first phragmocone chamber of Sphooceras with those in

embryonic shells of nautiloids, although it is only rarely

preserved in fossil nautiloids. Three nautiloid specimens

displaying this feature are from the Silurian of Bohemia

and Gotland. The first one is an oncocerid, namely

“Cyrtoceras”parvulum Barrande, 1866 (Barrande 1877,

pl. 504, figs 1, 2). The second one is an undetermined

oncocerid deposited in the Shary collection. The third

one is a Pentameroceras mirum (Barrande, 1865), from

the Silurian of Gotland (see Turek & Manda 2011,

fig. 6a). Although it is difficult to determine exactly the

hatching phase in these shells, the adapical part of the

embryonic shell of Pentameroceras,“Cyrtoceras”

parvulum and the undetermined oncocerid is dark with

transversal light coloured bands, and the colour pattern

consists of undulating bands near the presumed aperture

of the embryonic shell. The juvenile colour pattern ob-

served in all these specimens differs markedly from

those of the postembryonic growth stages. In the Recent

Nautilus, the shell is initially ivory coloured and the typ-

ical white-brown colour pattern appears gradually, first

on the flanks and later on the venter, about a quarter to

half a whorl before the nepionic constriction (Stenzel

1964, Arnold et al. 1987b). The colour pattern in

S. truncatum has a distinct beginning at the margin of the

plugged siphonal opening – the stripes are straight, not

interrupted, and clearly defined.

The development of colour stripes only on the dorsal

half of the shell has been documented in a few Early

Palaeozoic orthocerids and pseudoorthocerids (Ruede-

mann 1921, Teichert 1964, Turek 2009, Manda & Turek

2009) and one Ordovician endocerid (Balashov 1964).

Some authors (Ruedemann 1921, Flower 1955 and others)

have assumed that it is a characteristic of the majority of

orthocerids, indicating horizontal life position of the shell.

However, data are scarce concerning the colour pattern

in this group of cephalopods. In the Silurian pseudo-

orthocerid “Orthoceras”pelucidum Barrande, 1868 with

a slightly curved adapical part of the phragmocone and in

the related species “Orthoceras”columnare Marklin from

Gotland, longitudinal stripes are present around the entire

circumference. A specimen of Dawsonoceras annulatum

(Sowerby, 1816) shows the same characteristic. A recently

discovered colour pattern in two earlier Devonian

(Lochkovian) straight-shelled cephalopods from Central

Bohemia (Turek 2009) also shows its development around

the entire circumference of the shell. Both specimens, be-

longing perhaps to separate species, are fragments flat-

tened in shale, so their internal morphology, which could

indicate their living position, is unknown. Regardless

of the scarcity of data concerning the colour pattern in

cephalopods with straight or very slightly curved shell, it

appears reasonable to assume that colouring of shells re-

flects aspects of their autecology. Cephalopods with colour

pattern around the entire circumference of a straight shell

780

Bulletin of Geosciences  Vol. 87, 4, 2012

might indicate a vertical life position (Manda & Turek

2009) while cephalopods keeping their shell horizontal

might have had the colour pattern only on the dorsal side of

the shell (Flower 1955, Furnish & Glenister 1964); this is

also case of Sphooceras.

Embryonic shell in Sphooceras

Sphooceras shells that are definitely embryonic have not

been reported. In his discussion concerning this genus,

Dzik (1984) wrote that “the apical part of the shell of

781

Figure 6. Relations between selected parameters of shell in Sphooceras truncatum; notice linear correlation between individual parameters.

DV – dorsoventral. All measurements are in mm. For data see Table 1.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Sphooceras appears to be a protoconch, an interpretation

supported by the lack of any broken-off orthoceratid shell

fragments that might be referred to Sphooceras… If the en-

tire ovate apical part of the shell is an embryonic shell, the

egg must have been greater in size than the mature shell

aperture! Since this could not be the case, the larva must

have developed outside of its egg capsule…” (p. 135). He

characterised the family Sphooceratidae as nautiloids with

“very short, straight, compressed shell with very

large-sized protoconch (?), and cameral deposits with ra-

dial microstructure” (p. 141). However, in a later discus-

sion (1987, p. 225), he rejected this speculation concerning

the identification of the apical part of Sphooceras as a

protoconch. Teichert (1964), based on Barrande’s observa-

tions, noted the lack of truncated parts of phragmocones,

and stated that only the mature portion of the conch of

Sphooceras truncatum is known with certainty. Furnish et

al. (1962) noted several species of “Orthoceras” which

could possibly represent deciduous portions of the conch in

S. truncatum. Actually, as was already mentioned above,

isolated apical parts of phragmocones belonging to this

species and representing different ontogenetic stages

(including nepionic ones) occur frequently in the Silurian

cephalopod limestone of the Prague Basin, and probably

do represent deciduous portions of shells.

Barrande (1860, 1868) and Turek & Marek (1986) il-

lustrated shells of different growth stages in Sphooceras

truncatum (fig. 3, p. 251) from lower parts of the Kopanina

Formation. The dorsoventral diameter in specimens un-

equivocally assigned to S. truncatum ranges from

2–80 mm, with a maximum reconstructed shell length of

260 mm. Such a size range of the apical part was presented

as one piece of evidence for truncation.

The material preserved in yellowish, heavily weathered

cephalopod limestone from the Draská Gorge locality near

the village of Zadní Kopanina contains different growth

stages of S. truncatum. Nautiloid shells, unsorted by size,

are rather chaotically deposited (Fig. 18). In this

cephalopod assemblage analysed by Manda (2003, p. 92),

S. truncatum is the second most common species (20.4% of

collected shells). Associated orthocones have longicone

smooth shells, circular in cross section, usually with rather

long phragmocone chambers. Kopaninoceras sp. prevails

in the assemblage, with 30% of the collected shells. How-

ever, it is not clear whether one or several species of

Kopaninoceras are present here. Less common is a

longicone nautiloid with a markedly compressed shell,

oblique straight sutures and densely spaced phragmocone

chambers (Plagiostomoceras sp., 11% of collected shells).

Sphooceras co-occurs here with very small embryonic

shells of straight-shelled cephalopods representing growth

stages shortly after hatching (Figs 17, 19). All these speci-

mens of S. truncatum are of a similar size, their length is 4

to 5 mm and they markedly resemble adult specimens in

shape. The spherical initial chamber is very small and is

separated from the adjacent chamber by a conspicuous

constriction. A faint constriction is recognizable roughly in

the midpoint of the body chamber. The best-preserved

specimen shows 7 to 8 phragmocone chambers and a rela-

tively long body chamber. The shell is annulated; this

annulation appears to be suppressed adaperturally and is

not expressed on the internal mould.

Embryonic shells with a spherical initial chamber sepa-

rated from the adjacent part of the shell by a marked con-

striction are characteristic for the subfamily Sphaerortho-

ceratinae Ristedt, 1968, and bactritoids as well as

ammonoids (Ridstedt 1968). Embryonic shells of Sphoo-

ceras particularly resemble embryonic shells of Para-

sphaerorthoceras Ridstedt, 1968. However, no later

growth stages of cephalopods, which could be assigned to

Parasphaerorthoceras or related straight-shelled cephalo-

pods have been collected from the locality mentioned

above. Kolebaba (1973) illustrated similar types of embry-

onic shells from the early Homerian stage of the Prague

Basin. These specimens, preserved as internal moulds,

show no annulation, but were not systematically evaluated.

Plagiostomocerids have similar embryonic shells with

small spherical embryonic chambers less than 1 mm in dia-

meter, separated from later growth stages by a constriction.

They are probably related to the Sphooceratidae (Manda &

Frýda 2010).

In the Draská Gorge locality near the village of Zadní

Kopanina, both the preservation of different growth stages

of S. truncatum (including juvenile specimens with a

dorsoventral diameter of 2 to 3 mm and adults with a

dorsoventral diameter 20 to 30 mm) and a comparison of

some common morphological features of embryonic and

adult shells present in the taphocenosis support the idea

that the embryonic shells, so far not precisely identified,

belong to Sphooceras truncatum. All other co-occurring

782

Figure 7. Sphooceras disjunctum (Barrande, 1868). Ludlow, Neodiversograptus nilssoni Zone, Praha-Butovice, Kopanina Formation. Specimens sec-

tioned in median plane.•A–specimen NM L 40938a, phragmocone and adjacent part of body chamber; note great differences in in length

of phragmocone chambers. • B, C – specimens NM L 40937a and NM L 40937b; detail of outer shell-wall in adapertural part of body chamber. Note ex-

tremely thin shell near aperture and thickening of peristome. • D, G – specimen NM L 40937; detail of shell-wall showing place of truncation (comp. also

Fig. 13B), thickened cameral deposits forming apical callus and plugged or, what is more probable, eccentrically lying siphonal opening. • E, F – speci-

men NM L 40737; internal structures of shell; suborthochoanitic to cyrtochoanitic siphonal necks and very thin apical callus.•H–specimen

NM L 40938a; detail of adapical part of the shell with apical callus. Scale bar: 2 mm.

Bulletin of Geosciences  Vol. 87, 4, 2012

783

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

cephalopod species at this locality have different types of

embryonic shells. The presence of annulation in the embry-

onic shell, which has not been observed in later growth

stages of Sphooceras does not exclude this possibility; in

postembryonic growth stages, annulation frequently disap-

pears (Ristedt 1968, Kröger 2008). Weakening of an-

nulation in adapertural direction is another feature ob-

served in these juvenile growth stages. As shown by

Ristedt (1968), the taxonomic value of annulation is very

limited in some orthocerids.

Anomalous growth

Repaired damages of the apertural margin occur very fre-

quently in Recent Nautilus (e.g. Ward 1987) and were also

very common among fossil cephalopods with an outer

shell. However, due to the usually entirely smooth shell

surface in Sphooceras, the chance to detect healed injuries

or other anomalies of the shell is limited. In specimens with

well discernible growth lines, typical V-shaped injuries,

usually interpreted as a result of biting (e.g. Klug 2007),

have not been found.

A strange anomaly can be seen in specimen NM L

40963 (Fig. 5L, N). A lobe-shaped thickening of the

smooth shell on the flank crosses the border between the

apical part and the adjacent part of phragmocone. Con-

tinued traces of this injury are evident further along the

shell, in subsequent growth stages. There is a shallow lon-

gitudinal furrow nearby. It is presumed that the damage to

the shell was repaired by apposition of shell material by the

inner mantle surface. In another specimen (NM L 40964),

an anomaly has been found in the internal mould of the

phragmocone, more likely a result of anomalous growth

than of taphonomic processes. This injury looks similar as

sublethal damages of the shell observed on internal moulds

of Devonian bactritoids (Klug 2007).

Marked anomalies in the course of growth lines were ob-

served in the embryonal shell of specimen NM L 40965

(Fig. 17C). Just behind the protoconch, small ribs on the lat-

eral side are not transversal but markedly obliquely oriented.

A similar feature was documented by Ristedt (1968) in

Parasphaerorthoceras. This anomaly of growth might have

occurred inside the egg capsule, perhaps due to deformation

on the bottom, an explanation corresponding to the shell

anomalies observed in Cretaceous nautiloids (Chirat 2001).

Palaeobiology of Sphooceras

Origin of cameral deposits and their function

Cameral deposits in orthoceracone cephalopods belong to

the most widely discussed structures (e.g. Flower 1955,

784

Figure 8. Sphooceras disjunctum (Barrande, 1868). • A, B, E–G – Pra-

ha-Butovice, Ludlow, Neodiversograptus nilssoni Zone, Kopanina For-

mation. • C, D – specimen NM L 40976, Praha-Butovice, Kační Quarry,

Wenlock, Testograptus testis Subzone, Motol Formation. • A, B – speci-

men NM L 40975; almost complete young growth stage, partly exfoliated,

with very low first chamber; dorsal and lateral views. • C, D – specimen

NM L 40978, annular elevation; dorsal view.•E–thesame specimen as

in Fig. 8A; detail of detachment zone. • F, G – lectotype NM L 17549, il-

lustrated by Barrande (1868, pl. 345, figs 11, 12); ventral and dorsal

views. Scale bar: 10 mm.

Bulletin of Geosciences  Vol. 87, 4, 2012

785

Figure 9. Sphooceras truncatum (Barrande, 1860); drawing of specimens sectioned in median plane; some of them illustrated also in Fig. 3.•A–speci-

men NM L 40924, Ludlow, Zadní Kopanina, Kopanina Formation; very thick cameral deposits.•B–specimen NM L 40929, Ludlow, vicinity of Prague,

Kopanina Formation; thick cameral deposits. Concave part of the 2th preserved septum covered by a thin layer of episeptal deposits, perhaps representing

initial stage of their growth preceding truncation.•C–specimen RM Mo 42513, Ludlow, Sandarve Kulle, Gotland, Hemse beds, upper part. Grow stage

early after truncation; slightly developed cameral deposits form a thin layer.•D–specimen MCZ 160432, Kosoř, Ludlow, Kopanina Formation; besides

strong deposits forming the apical callus, primary cameral deposits (both episeptal and hyposeptal) almost completely unfilled the 5th phragmocone

chamber.•E–specimen RM Mo 42801, Wenlock, Othem, Gotland; progressive shortening of phragmocone chambers during growth of the shell. De-

spite the presence of 7th phragmocone chambers apical callus is unusually thin.

CDE

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

1964; Seuss et al. in press) and have been subject of contro-

versial opinions. Several principal questions concerning

these structures were discussed: Are they primary, i.e. pre-

cipitated by the animal itself, or are they of secondary na-

ture originating from post-mortem processes? If both types

of cameral deposits are present, which of them belong to

the former and which to the later type? If they are primary,

were they precipitated from extrapallial fluids, which pe-

netrated the chambers through the siphuncle, or is their ori-

gin owed to soft tissue, which was in direct contact with

them?

The theory of the primary origin of cameral deposits,

first expressed by Woodward (1851) and substantially sup-

ported by Barrande (1866), has been widely but not quite

unequivocally accepted, and was the subject of controver-

sial opinions (see discussion in Mutvei 1956, 2002 and

Crick 1982). The main arguments for their primary secre-

tion were summarised by Flower (1964) and Teichert

(1964); important supporting observations were added

later (e.g. Fischer & Teichert 1969, Crick 1982, Bandel &

Stanley 1989, Blind 1991, Histon 1993). Today, based on

new supporting evidence, primary secretion of cameral de-

posits is considered beyond dispute (Seuss et al. 2011).

A somewhat controversial theory of the cameral mantle

expressed by Flower (1939) was refused by some cepha-

lopod workers (e.g. Mutvei 1957, Dzik 1984) and was sub-

stantially supported by further investigation of Flower

(1941, 1955, 1964), Teichert (1964), Holland (1965),

Histon (1993), Kolebaba (1999, 2002), as well as Zhu-

ravleva & Doguzhayeva (2002). Sphooceras can contrib-

ute significant data for the discussion of these questions.

Contrary to other straight-shelled cephalopods with a long

phragmocone, cameral deposits are developed only in the

“first” phragmocone chamber. Their primary origin in

Sphooceras is confirmed by their development during on-

togeny, internal structure, form and location inside the

shell. As in other othoceratoids with long phragmocone,

cameral deposits are more developed ventrally for stability

and equilibrium, i.e. to help hold the animal horizontal

(presuming they managed to achieve neutral buoyancy

with the little amount of phragmocone chambers). Their

growth due to this function had to be physiologically con-

trolled. Their appearance in a phragmocone chamber other

than in the adapical one is interpreted as a temporary condi-

tion, usually preceding truncation. A single specimen

showing both episeptal and hyposeptal cameral deposits in

one phragmocone chamber located near the centre of grav-

ity (specimen MCZ 160432 L40929) is exceptional. Vas-

cular imprints on the surface of cameral deposits and on the

convex surface of the first septum support the hypothesis of

the presence of a cameral mantle; soft tissue entered into

the adapical chamber through an opening in the siphuncle

in this chamber. It seems probable that cameral deposits

evolved repeatedly and independently in unrelated evolu-

tionary lines, and thus their morphology and mode of for-

mation may vary profoundly.

Apical callus, vascular imprints

The first supposed step of formation of an apical callus was

secretion of cameral deposits on the concave part of the

septum (which later became septum of truncation) in the

adapertural half of the phragmocone. Development of ca-

meral deposits was accompanied with their fusion with

septum, which became structurally altered. A content of or-

ganic material in septum of truncation increased owing to

growth of organic radial lamellae inside the septum. Du-

ring this process the border between septum and deposits

disappeared. Then followed the formation of a calcareous

plug closing the siphuncle in this part of the shell. The sep-

tal opening was sealed gradually along the whole internal

circumference. It caused cutting of the adapically lying

part of phragmocone from the physiological – processes

preceded natural removal of the apical part of the phragmo-

cone from the rest of the shell. This hypothesis is based es-

pecially on the specimen Sphooceras disjunctum NM L

41032 (Figs 12B–D, 13A, D, E) in which boundary between

septum and growing cameral deposits disappeared. The

mantle of molluscs has the ability to secrete shell as well as

to remove what it has deposited (Carriker 1972), so remo-

val of the apical part of the shell during truncation could

have been done by chemical dissolution. The shell wall at

the separation boundary could have been chemically wea-

kened by the mantle edge. After this part was eroded, the

apical part of shell would fall away. Another, in light of

new observations less probable possibility considered is

that the site of truncation was area between septum and epi-

septal deposits. The connection between the septum and

the episeptal deposits, whose outer part is structurally dif-

ferent from their inner part, could be weakened prior to the

actual separation of the adapical part of the phragmocone

by the termination of metabolic processes in that part. It

may have enabled separation of the structures during the

truncation. In this case a new apex would be formed only

by episeptal deposits. The septum became a detached part

of phragmocone (further discussion see in part dealing with

truncation).

Symmetrical traces showing a characteristic pattern on

the concave surface of cameral deposits in S. truncatum are

occasionally preserved (Barrande 1860, 1870, pl. 341,

figs 18, 19; Kiselev et al. 1993, fig. 5; Figs 2H, 15A, C, D,

G, H, K, L, 16C, E, F, I, 20). A deep furrow is present mid-

ventrally and middorsally. The traces are clearly visible in

the infilling of originally empty space of the adapertural

part of the first chamber, and exceptionally also on the con-

vex surface of the first septum. They are interpreted as vas-

cular imprints of the cameral tissue entering the first

786

Bulletin of Geosciences  Vol. 87, 4, 2012

phragmocone chamber through the siphuncle. Similarly, in

Recent Nautilus “muscle fibres in the mantle as well as

blood vessels located within the septal mantle and on its

visceral side occasionally leave imprints on the inside of

the wall of the body chamber and the apertural side of

cephalopod septa” (Klug et al. 2008, p. 485). Their origin

is attributed to soft tissue responsible for the secretion of

these deposits.

787

Figure 10. Sphooceras truncatum (Barrande, 1865). • A, B – specimen NM L 40921b, Ludlow, Neodiversograptus nilssoni Zone, Praha-Butovice; first

chamber of adult specimen almost completely filled by cameral deposits and detail of siphonal opening; thin hyposeptal cameral deposits cover also free

part of septum and septal neck being more heavily developed ventrally, A (× 2.1), B (× 6). • C – specimen NM L 40919b, Ludlow (see Fig. 4),

Praha-Braník, Školní vrch, Kopanina Formation. Sagittal section, first chamber almost completely filled with cameral deposits, × 1.7.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Secretion of cameral deposits probably resulted from

the opening of the thin uncalcified connecting ring into the

first phragmocone chamber – a phenomenon discussed and

documented in detail for some other straight-shelled

cephalopods by Kolebaba (1999a, b, 2002). His observa-

tion supports Flower’s idea (1941, 1955) about a direct

connection between the siphonal tissue and the cameral

mantle.

The presence of soft tissue in the first phragmocone

chamber of Sphooceras is well documented by Barrande’s

illustrations (Barrande 1868, pl. 341). The space that was

available for the soft tissue initially lining the first

phragmocone chamber gradually became smaller, as the

cameral deposits grew. The free space acquired an irregu-

lar, flattened lenticular shape.

Outer layers covering the callus

and their origin

The following scheme of secretion of additional calcareous

layers on the outer shell surface is proposed: as the mantle

completely covered the shell, it initially deposited a layer

with roughly concentric wrinkled striae, in a somewhat

fingerprint-like pattern, on the exposed cameral deposits.

The plugged siphonal opening shows finer striae, in a more

geometrically precise concentric pattern; in some speci-

mens, fine radial striae are also discernible. An interesting

feature of the layer with the fingerprint pattern is a disrup-

tion in the course of the individual striae by V-shaped inva-

ginations, situated on the ventral and dorsal sides of the

conch, but not always in the plane of symmetry (Figs 2M,

5F, 15J, 16B). These may indicate places where two exten-

ded mantle lobes met. With regard to the position of this

layer on the shell and supposed mode of secretion the layer

is compared with the nacreous layer in other cephalopods.

In agreement with published opinions concerning the wrin-

kle layer in ammonoids, bactritoids and nautiloids (Dogu-

zhaeva & Mutvei 1986), wrinkles might have served for

the attachment of the mantle and to control its movement in

this region during secretion of layers on the “naked” con-

vex surface of the cameral deposits. A very thin layer bear-

ing a colour pattern in the dorsal half of the shell then over-

laid the wrinkled layer. The mode of secretion of these two

layers on the outer shell surface could have been similar to

cypraeid gastropods (see Savazzi 1998) in which the shell

has been temporarily completely covered by mantle and a

new layer was deposited on the surface. Similarly some

bellerophontoids had a part of the last whorl cowered by

mantle extended from the aperture as it can be indicated

from the morphology of their shell (Harper & Rollins 1985,

Frýda & Gutiérrez-Marco 1996).

In some specimens of S. truncatum, the finger-pattern

layer is missing (e.g. Barrande 1868, pl. 343, figs 11–13)

and the surface of the apical part of the shell is radially stri-

ated (Figs 2O, 16H). In the case where no additional layers

were deposited, such a shell can be interpreted as that left

by the animal dying just after truncation, or as a result of

secondary dissolution of both layers – the finger-pattern

layer and smooth outer layer with the colour pattern. Simi-

larly, in some specimens studied, the finger-pattern layer

was the last one to form the outer surface of the apical re-

gion (Figs 5B, F, 15B, J). As the outer layer was very thin

in the apical part of the shell, this state of preservation

probably resulted from partial or complete dissolution of

the outer layer during post-diagenetic processes or from

weathering. The radially striated layer (specimen MCZ

788

Figure 11. Sphooceras truncatum (Barrande, 1865). Incomplete speci-

mens cut in median plane; see also Fig. 9C, E. • A, B – specimen RM Mo

42513, Ludlow, middle Ludfordian, O. sagitta Zone, Sandarve Kulle,

Gotland, Hemse Beds, upper part. • C, D – RM Mo 42801, Wenlock,

Sheinwoodian, Slite beds, Othem, Gotland. Different stages of develop-

ment of cameral deposits. The convexity (high) of the first phragmocone

chamber is highly variable. Scale bar: 10 mm.

Bulletin of Geosciences  Vol. 87, 4, 2012

160328) can be sometimes seen just under the translucent

outer shell wall, especially in the abapical part of the first

chamber. It seems probable that in this part of the shell, the

secretion of the layer with roughly concentric wrinkles was

suppressed. The finger-pattern layer has not yet been ob-

served in any S. disjunctum.

Secretion of additional calcareous layers in the remain-

ing part of the shell during mantle extension was very lim-

ited. It is possible that secretion of these layers probably

proceeded from the apex down as the uppermost layer is re-

duced abapically (Barrande 1860). If this thin layer was de-

posited on the whole surface of the shell is not clear but this

could explain why the shell surface in Sphooceras is usu-

ally entirely smooth, or with hardly discernible growth

lines (e.g. Figs 2A–G, 5B–D, L–N), lacking typical healed

damages of the shell so frequently occurring in nautiloids.

It is supposed that the pigment-bearing layer in Sphooceras

was confined to the outermost portion of the shell wall, as

in present day Nautilus (Valenciennes 1841). Although

only fragments of the shell are preserved in the second and

third chambers of the specimen discussed, the absence of

any traces of colour pattern in the adjoining part of the

phragmocone is remarkable. It may indicate that secretion

of the layer bearing the colour pattern did not exceed the

789

Figure 12. Sphooceras truncatum (Barrande, 1868). Ludlow, Kopanina Formation. Specimens sectioned in median plane. Ludlow, Neodiversograptus

nilssoni Zone, Praha-Butovice, Kopanina Formation.•A–specimen NM L 41313; notice thin apical callus and crater-like depression in place of plugged

siphuncle. • B–D – specimen NM L 41032; B – incomplete phragmocone [apical chamber(s) missing], C, D – details of last two septa; notice thickened

next-to-last septum, owing to fusion of septum with episeptal deposits (comp. also Fig. 13A, D, E). Scale bars in A and B equal 5 mm, C andD2mm.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

borderline separating the apical region of the shell from the

rest of the phragmocone. It shows that the secretion of the

outermost shell layer was not a uniform process; the layer

covering calcareous deposits forming the callus was

formed after truncation.

In Sphooceras, the internal structure and the possible

covering of the shell by the mantle in some growth stages

of the shell indicate an analogy with the rostrum of belem-

nites, an idea already expressed by Barrande (1860).

Truncation  an overlooked feature

of cephalopod evolution

Contrary to soft-bodied coleoids, the maximum evolutio-

nary size of externally shelled cephalopods might have

been constrained by physiological limits. The shell size

was one of the features, which also affected its physical

properties, such as resistance to hydrostatic pressure,

drag, and hydrodynamics. In straight-shelled possible

planktonic cephalopods, some shells with low expansion

rates occurring in Prague Basin reached huge diameters

(200–250 mm) and it is hard to imagine that the creature

inside could handle such a shell. The morphological fea-

tures of the shells also strongly influenced swimming mo-

des of the shells. Several cephalopod lineages evolved a

common solution to this problem: rejection of the apical

part of the phragmocone, namely truncation. This perhaps

common mode of shortening of the phragmocone is not

yet well understood. Development of an anomalous sep-

tum and closing of the siphonal tube usually preceded

truncation.

Truncation in Sphooceras

Due to the discrepancy of opinions concerning the trunca-

tion in cephalopods, the question has been reopened (Turek

790

Figure 13. Drawing of specimens sectioned in median

plane. • A, B, D, E – Sphooceras disjunctum (Barrande,

1868). Ludlow, Neodiversograptus nilssoni Zone, Pra-

ha-Butovice, Kopanina Formation. • A, D, E – specimen

NM L 41032; A – incomplete phragmocone and adjacent

part of body chamber; apical chamber(s) missing; D – de-

tail of last two chambers; outer shell wall partly exfoliated

during collection; E – part of septum fused with episeptal

deposits.•B–specimen NM L 40938a (see also Fig. 7A,

D), detail of ventral side.•C–Sphooceras truncatum

(Barrande, 1860); specimen NM L 40919A; Ludlow, lat-

est Gorstian or earlier Ludfordian, Praha-Braník, Školní

vrch, Kopanina Formation; detail of dorsal side (see also

Fig. 4). Arrows indicate site of truncation. Not in scale.

Bulletin of Geosciences  Vol. 87, 4, 2012

2007). Existence of this process in Sphooceras is supported

by the following observations:

a) The shell has a very short phragmocone with a lim-

ited number of phragmocone chambers – three to eight

(documented in specimens of S. truncatum with measured

dorsoventral diameter ranging from 2 to 85 mm (early ju-

venile growth stages possessing protoconcha and probably

belonging to Sphooceras are not included) and three to five

in S. disjunctum with dorsoventral diameter ranging from

12 to 31 mm;

b) A characteristic structure of the apical portion of the

shell contains a strongly narrowed and then plugged

siphonal perforation and thickened apical end of the shell

in different ontogenetic stages. A different pattern on the

surface of the apex is sometimes due to exfoliation of a

layer or may be a result of a primary condition – death of

the animal just after truncation or in different stages of se-

cretion of outer layers;

c) Two shell layers cover the convex apical surface

formed by naked cameral deposits – the inner one with the

characteristic finger print pattern and the outer layer, which

is smooth;

791

Figure 14. Sphooceras truncatum (Barrande, 1865), Ludlow, Kopanina Formation, Bohemia. Specimens sectioned in median plane, details of apical

parts; A–F – notice strong asymmetry of cameral deposits, differences in their thickness, shape, their radial structure and orthochoanitic to

suborthochoanitic septal necks.•A–specimen NM L 40932a, Zadní Kopanina, × 2.7; see also Fig. 3A.•B–specimen 40928a, vicinity of Prague, × 2.9.

• C – specimen NML 40926a, Zadní Kopanina, × 3.4. • D – specimen NM L 40927a, Zadní Kopanina, × 3.7.•E–specimen NM L 40933a, Zadní

Kopanina, × 2.6.•F–NML40925a, vicinity of Prague, × 3.6.•G–NML40979, Zadní Kopanina, × 3.8.•H–specimen MCZ 160432, Kosoř; besides

apical callus both episeptal and hyposeptal deposits present in 5th phragmocone chamber, × 2 (comp. also Figs 3F and 9D).

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

d) Discontinuity of growth can be traced in the bound-

ary between the truncated part and the rest of the shell – an-

nular groove and sometimes thickening of the shell along

this boundary, disrupted course of growth lines and sudden

disappearance of colour pattern,

e) Discontinuity in the structure of the shell wall has

been observed in polished sections;

f) Presence of episeptal deposits in one another

phragmocone chamber (besides the first chamber) was dis-

covered in two specimens – a supposed symptom preced-

ing later truncation;

g) Complete shells of Sphooceras co-occur with iso-

lated apical parts, which may represent truncated portions

of the shells;

h) Findings of early juvenile shells having to 6 to 8

phragmocone chambers.

As it is indicated in one specimen S. disjunctum cut in

medium plane (NM L 41032, Figs 12B–D, 13A, D, E) thin

episeptal deposits gradually fused with adjoining septum so

that the border betweem septum and deposits disappeared.

The septum is markedly thickened, its colour is dark brown;

its original structure was probably changed. Next steps of

growth of cameral deposits are supposed: In subsequent

stages the content of organic matter in cameral deposits

markedly increases forming radial lamellae and the compos-

ite structure septum-episeptal deposits changes into new

shell structure – apical callus. Formation of a calcareous

plug closing the septal foramen follows. Secretion of these

structures preceded the periodic natural removal of the api-

cal part of the shell, comprising four to five phragmocone

chambers in S. truncatum and two or perhaps even only one

in S. disjunctum.InS. truncatum, the episeptal deposits were

secreted in the 5th or 6th chamber and in S. disjunctum with

wery short phragmocone in the last or penultimate chamber.

Adapical part of the shell has to be uncovered by the mantle

before truncation. Whether the mantle was completely or

only partially retracted into the body chamber before trunca-

tion is not clear. The annular belt bordering the first chamber

is interpreted here as the detachment zone. After truncation,

the mantle might have completely surrounded the new apical

region and secreted the two additional calcareous layers

mentioned above. The ability of the animal to repeatedly en-

tirely cover its shell with its mantle in these growth stages

was facilitated by a very short phragmocone and a long body

chamber (see also Kröger 2002). This process is substanti-

ated by the discovery of a colour pattern in the apical region

of the shell, which could not have been secreted by cameral

mantle (comp. Gnoli & Kiselev 1994) as the siphonal open-

ing from which siphocameral tissue could be theoretically

expanded was already plugged. Also, it seems highly im-

probable that this internal tissue contained pigments cells

having ability to secrete colour pattern. Dark brownish lon-

gitudinal stripes are present on the dorsal half of the shell

only. This pattern, together with the general morphology of

the shell supports the idea of a horizontal living position in

this cephalopod, for which nectonic or nectobenthonic mode

of life is presumed. Functionality of the colour pattern de-

pends on its visibility, so the soft tissue covering the new

apex may have been translucent, or the mantle was retracted

from the new apex after secretion of the outer layer contain-

ing colour pigments. The camouflage effect would have

been improved by pigmentation of the soft tissue.

Based on the number of phragmocone chambers in indi-

vidual specimens and the size of the largest ones, Barrande

(1860) estimated that truncation, during which Sphooceras

truncatum losted three to five phragmocone chambers could

have happened about 50 times during ontogeny of the largest

specimens, which, without truncation would have attained a

length of 160 cm. Barrande (1872) amended this opinion,

calculating that having the dorsoventral diameter 80 mm and

average apical angle 8° would result in a total shell length

(without truncation) of about 530 mm. Truncation then

could have been repeated 24 times. According to our investi-

gation, based on a recently discovered specimen, the total

length of this largest known specimen possessing 8

phragmocone chambers was only about 260–270 mm and

total shell length without truncation would have been about

700 mm). We consider constant apical angle 8°, and body

chambere representing one and half of the length of

phragmocone (i.e. 8 phragmocone chambers).

792

Figure 15. Sphooceras truncatum Barrande, 1860; A, B, D–F, H–M – Ludlow, Kopanina Formation, C, G – Wenlock, Gorstian, Motol Formation,

Testograptus testis Subzone. • A, D, I, L – specimen NM L 40943, Praha-Butovice, Neodiversograptus nilssoni Zone; incomplete phragmocone, apically

partially exfoliated with preserved replica of cameral deposit surface, with impression of vascular tissue; apical (A), oblique apical (D), dorsolateral (I)

and lateral (L) views; note detachment zone and abrupt ending of shell sculpture due to truncation.•B–specimen NM L 40962, Beroun, Kosov Quarry;

apical part of shell covered by finger-print pattern layer bearing crinoid holdfast. • C, G – specimen NM L 40961, Praha-Řeporyje, Arethusinová Gorge;

apical part of shell; replica of cameral tissue surface, frontally with relict of finger-print patterned-layer, lateral (C) and oblique apical (G) views.

• E, F – unfigured paratype of “O. sarcinatum” Barrande, 1868, Neodiversograptus nilssoni Zone; apical part. First septum from internal (concave) side

(E); note radial structures of cameral deposits close to margin; weathering of convex surface reveals spongious structure of cameral deposits, radial struc-

tures and fragment of layer with finger-print pattern close to the right margin (F). • H, K – specimen NM L 9180 illustrated by Barrande (1868, pl. 341,

figs 1–5), see also Fig. 2H in this paper, Zadní Kopanina, Zmrzlík; apical part with replica of cameral tissue on concave surface of almost completely re-

moved cameral deposits, preserved on sparitic infilling of first phragmocone chamber. • J – lectotype NM L 9184, Praha-Butovice, Neodiversograptus

nilsoni Zone; finger-print pattern on apical part of shell; note asymmetrically located V-shaped invagination of wrinkles; see also Fig. 2M in this paper.

• M – specimen NM L 9193, Zadní Kopanina; detail of apex showing infilling of septal perforation (plug). Scale bar: 5 mm.

Bulletin of Geosciences  Vol. 87, 4, 2012

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Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Truncation in other cephalopods: comparison

with Sphooceras

Truncation is thought to have evolved independently in

some other cephalopods besides Sphooceras. Barrande

(1860) mentioned some other straight-shelled cephalo-

pods, one oncocerid (gomphocerid) and ascocerids in

which he considered truncation a certainty, and subsequent

researchers confirmed this conclusion. Flower (1964) was

also convinced of the process in Ecdyceratida. Furnish et

al. (1962) mentioned truncation in the Carboniferous or-

thocerid Brachycycloceras, but in this case, Niko & Mapes

(2010) raised doubts. Stridsberg (1985) documented trun-

cation in three brevicone oncocerid species from Gotland.

Truncation in ascocerids was supported by Lindström

(1890) on the basis of well-preserved specimens from

Gotland. He supposed that the ascocerid phragmocone was

broken off several times during ontogeny, a theory later

widely accepted (Flower 1941, 1963a; Furnish & Glenister

1964; Holland 1999). Frye (1982, p. 1275), studying Ordo-

vician ascocerids, stated that it was not certain “whether

truncation occurred ontogenetically or post-mortally” in

these nautiloids and Dzik (1984, p. 111, 135) briefly dis-

cussing this problem in context with Sphooceras as well as

the Ascoceratidae and Brachycycloceras concluded: “One

cannot suggest any reasonable mechanism of shell trunca-

tion.” The fact that, with a few exceptions, the “ascoceras

stage” occurs separately from the “cyrtoconic stage” of the

shell (sensu Lindström) he explained as secondary, caused

by sampling. In Brachycycloceras he supposed that trunca-

tion is insufficiently supported.

Although ascocerids are generally very rare fossils, sur-

prisingly rich material containing 71 specimens was gath-

ered during recent fieldwork by Ladislav Zedník, Štěpán

Manda and Ladislav Čížek in the Prague Basin. None of

the specimens has the juvenile part of the shell, and careful

fieldwork excludes the possibility that the juvenile part was

lost during excavation. Holland (1999) concurs with earlier

researchers regarding truncation in Ascoceras. In discard-

ing the adapical cyrtoconic part of the shell, the animal ac-

quired a more streamlined shell shape with greater resis-

tance to mechanical damage by shallow sea dynamics

(see also Holland 1999, Gnoli & Kiselev 1994). Solid

evidence for the truncation in the Ordovician ascocerids

was recently given by Kröger (2007).

Although truncation in Sphooceras achieved similar re-

sults to the supposed truncation in the above-mentioned

nautiloids, the actual processes differ substantially:

As the real apex of Sphooceras is never formed by typi-

cal septum, Turek (2007) supposed that the septum of trun-

cation remained with the discarded portion of the shell.

However, separation of septum from adjacent episeptal de-

posits during truncation has not been explained in a satis-

factory manner. On the other hand the structure of cameral

deposits forming apical callus and structure of septa differs

substantially and therefore natural detachment of both

layers could be possible. Owing to discovery of an excep-

tionally well-preserved specimen of S. disjunctum a more

realistic alternative discussed above is proposed. In the re-

maining portion of the shell, the apical end was formed by a

composite shell part – septum fused with episeptal depos-

its. During continued growth of the animal, secretion of

two additional layers followed, overlying the callus from

the outside. The inner fingerprint pattern layer (thought to

be the nacreous layer) and smooth outer layer (with colour

pattern, thought to be the outer prismatic layer) were se-

creted by the mantle, extended from the body chamber.

In ascocerids, a thickened septum of truncation formed

after decollation of the apical end of the mature shell, and

probably no additional layer was deposited on its outer sur-

face. A long body chamber as well as the position of the

phragmocone above the body chamber in the late growth

stage theoretically enabled extension of the mantle to pro-

tect the thin-walled shell. However, if some fragments of

the deciduous shell remained attached to the part occupied

by the living animal, they would have prevented covering

of the septum of truncation by soft tissue (Furnish &

Glenister 1964). In any case, no proof has been found for

extension of the mantle in ascocerids.

Stridsberg (1985, pp. 16–18) discussed in detail the

truncation in the two oncocerid genera – Trimeroceras and

Pentameroceras. The septum of truncation in these “gom-

phocerids” is thicker and more strongly curved than other

septa. He mentioned and illustrated the specimen just be-

fore truncation; the septum of truncation is not the last pre-

served, but next to last. Interestingly, the shell wall in the

794

Figure 16. Sphooceras truncatum, Ludlow, Kopanina Formation, Bohemia; details.•A–specimen NM L 21467 illustrated by Barrande (1870, pl. 448,

figs 3–5), Fig. 5I herein, Slivenec, valley; detail of surface in adapical part of shell with growth lines, detachment zone and radial structure of cameral de-

posits emerging here to the surface, × 5.•B–specimen NM L 9194, illustrated by Barrande (1868, pl. 343, figs 4, 5); apex showing plugged siphonal

opening and surrounding deposits (smooth layer), sharply delimited from finger-pattern layer, × 5.7. • C, E, F, I – natural cast of vascular imprints on the

concave surface of cameral deposits; lateral, top and oblique views; C – specimen NM L 9180 illustrated also in Figs 2H, 15H, K, Zmrzlík, × 8.9.

• D, G – specimen NM L 40922, Praha-Butovice, Neodiversograptus nilssoni Zone; D – spongious structure of cameral deposits in “O. sarcinatum”, seen

on their weathered surface; apical view, see also Fig. 15F, × 6; G – the same specimen, radial structure on the concave surface of cameral deposits, see also

Fig. 15E, × 3.3. • E, F – specimen NM L 40961, Praha-Řeporyje, Arethusinová Gorge, × 8.•H–specimen illustrated here also in Fig. 5C; detail of surface

of cameral deposits and detachment zone, × 4.8. • I – specimen NM L 40943, apical part with partly exfoliated shell with replica of soft tissue surface; see

also Fig. 15A, D, × 5.4.

Bulletin of Geosciences  Vol. 87, 4, 2012

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Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

oldest preserved chamber is much thinner than the shell

wall in the adjacent part of phragmocone. He states: “The

reason for this decreasing thickness might either be internal

resorption, or absence of the internal reinforcement occur-

ring in later chambers.”

Natural removal of the apical part of the shell by other

means than mechanical breakage is not limited to

nautiloids and straight-shelled cephalopods. Doguzhaeva

& Mutvei (1989) documented removal of the initial part of

the shell in heteromorphic lytoceratid Ptychoceras. Based

on investigation of the shell structure in this ammonoid,

they concluded that its shell might have been at least par-

tially covered by mantle during its lifetime. An interesting

case of truncation was described in Hematites, one of the

oldest-known (Early Carboniferous) coleoids (Dogu-

zhaeva et al. 2002). The initial portion of the phragmocone

was plugged by a central rod structure of the rostrum and

contained an additional septum. Some analogy with

Sphooceras can be found in this process, which was con-

cluded by the rostrum formation in Hematites.

It appears highly probable that the truncation of the api-

cal portion of the shell was much more widespread in Early

Palaeozoic cephalopods than was previously assumed.

Temporary encasement of the entire shell in Sphooceras is

here assumed as certain. Bandel & Stanley (1989) sug-

gested that the conch of the Devonian genus Atrhrophyllum

with characteristic deposits developed in posterior cham-

bers of the phragmocone might have been external as well

as internal.

Ecology of Sphooceras

Conclusions concerning its ecology are based especially on

the study of Sphooceras truncatum and S. disjunctum, the

best-known species of this genus. Early juvenile specimens

of Sphooceras may have lived as pelagic forms (Manda &

Frýda 2010). In discussions on buoyancy and swimming

activity of later growth stages, the following aspects have

been considered: a) general morphology; b) correlation

between shell growth, development of the apical callus of-

fering a counterweight to prolonged phragmocone and

length of the body chamber; c) a very short phragmocone,

which periodically changed its length and the ratio between

the length of the phragmocone and the length of the body

chamber; d) the formation of cameral deposits before trun-

cation; e) the colour pattern limited to the dorsal half of

the shell only, suddenly diminishing behind the area of

truncation.

It is speculated that Sphooceras was a nektonic or

nektobenthonic animal with neutral buoyancy, maintaining

its shell in a horizontal position (Fig. 21). This is supported

by the following features: a) hydrodynamic shape of the

shell with smooth surface; b) very thin shell walls, so that

the shell was very light; c) oblique course of the aperture to

shell axis; the dorsal side is thus longer, protecting the head

while the shorter ventral side gives more space for protru-

sion of the powerful hyponome; d) phragmocone possess-

ing cameral deposits and is always shorter than the body

chamber, so encasing of the whole shell by soft tissue was

possible; e) siphuncle is shifted slightly ventrally from the

centre, so that septa are vaulted more ventrally then dor-

sally; f) shapes of cameral deposits forming an apical callus

are in correlation with the prolongation of the

phragmocone; their thickness is greater in the ventral part

of the shell than the dorsal, giving the shell a preferred

floating orientation; g) longitudinal colour stripes are de-

veloped only on the dorsal part of the shell, creating a cam-

ouflage effect from above.

The proposed nektonic or nektobenthonic mode of life

corresponds with the opinion of Gnoli & Kiselev (1994),

who viewed truncation in Sphooceras as a “step towards

modern cephalopod evolution, obtaining a very stream-

lined body, such as modern coleoids, which supports its

manoeuvrability and more efficient swimming”.

Periodic shortening of the phragmocone may seem as a

traumatic event strongly disturbing supposed maintaided

horizontal position of the shell. However, it probably did

not significantly influence buoyancy. Although the animal

lost three or four phragmocone chambers at a time, positive

buoyancy of this part of the shell was gradually reduced by

progressively growing cameral deposits. The apical callus,

which was still only slightly developed at the time of trun-

cation, was perhaps sufficient for maintaining neutral

buoyancy and a horizontal life position of the shell after

truncation, i.e. centre of buoyancy was speculatively lo-

cated just above the centre of mass. Regarding the role of

cameral liquid in maintaining floatation equilibrium during

truncation, we can only speculate.

Cephalopods with straight shells have been considered

to have been active swimmers (Flower 1957, Furnish &

Glenister 1964, Teichert 1964), but according to some re-

cent views (Mutvei 2002) the dorsal position of their muscle

scars shows that their swimming ability was weak, possi-

bly even indicating a planktonic lifestyle (Mutvei 2002,

Kröger et al. 2005, Klug et al. 2010). The possibility of

negative buoyancy and a benthic mode of life of ortho-

cerids was proposed by Ebel (1999), but has not been

widely accepted. Some straight-shelled cephalopods, how-

ever, possess some very progressive features, similar to

coleoids (for summary see Mehl 1984, Engeser 1996,

Gabbot 1999). The question remains, whether the mecha-

nism of swimming in these cephalopods was the same as in

the Recent Nautilus. Rapid swimming in the Recent Nauti-

lus is produced by contraction of powerful retractor mus-

cles attached to the lateral sides of the shell wall in front

of the last septum, which pull the body into the shell.

This is accompanied by simultaneous contraction of the

796

Bulletin of Geosciences  Vol. 87, 4, 2012

hyponome (Mutvei 2002b). He stated that the contraction

of the retractor muscles in orthocerids attached to the dor-

sal side of the shell close to the last septum “could not be

used to expel water from the mantle cavity for swimming

by jet propulsion, as in Nautilus” (p. 391). Considering the

superficial similarity of Sphooceras and some other straight-

shelled cephalopods to some coleoids, it seems possible that

the mantle was also liberated to become a muscular pumping

organ that led to much more powerful jet propulsion, enabling

rapid swimming (see also Barskov et al. 2008).

Sphooceras was widely distributed during the Wenlock

and Ludlow in the tropical and subtropical shallow seas of

Baltica, Kazachstania, Avalonia and Perunica, even reach-

ing the somewhat colder waters of the peri-Gondwanan

797

Figure 17. A–D, G, H, I – possible early stage of Sphooceras truncatum (Barrande, 1860). Ludlow, Saetograptus linearis Zone, Zadní Kopanina,

Draská Gorge, Kopanina Formation; early growth stages of shell with preserved protoconchs; note marked constriction of protoconcha, slight constric-

tion of shell in lateral view, annuli fading adaperturally and unusual course of transversal sculpture (Fig. 17C).•A–specimen NM L 40966.•B–speci-

men NM L 40967. • C – specimen NM L 40968. • D – specimen NM L 40969. • G –specimen NM L 40970. • H – specimen NM L 40971. • I – specimen

NM L 40972, two juveniles – ventral and dorsolateral views. • E, F, J – Sphooceras truncatum (Barrande, 1860). Ludlow, Saetograptus linearis Zone,

Zadní Kopanina, Draská Gorge, Kopanina Formation.•E–specimen NM L 40973, damaged juvenile specimen associated with three phragmocone

chambers (?detached portion of shell) of larger specimen.•F–enlarged younger specimen illustrated in Fig. 17E.•J–specimen NM L 40 974, young

damaged specimen from lateral and dorsal views. Scale bar: 2 mm (A–I) and 5 mm (J–L).

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

basins (Fig. 22). Sphooceras ranges from early Wenlock up

to the Přídolí, with the most reliable fossil record appearing

in the Tian-Shan Mountains and Bohemia. In others basins,

Sphooceras occurs only in short intervals. Its abundance

varies strongly, depending on facies (Figs 23, 24). It occurs

very rarely in tropical carbonate platforms of Baltica and

Avalonia. The distribution pattern of Sphooceras is best

known from the Prague Basin. Sphooceras truncatum ap-

peared there in the early Homerian and continued to the

early Přídolí, with two Lazarus gaps after mass extinctions

(Lundgreni/ Mulde and Kozlowskii/ Lau events). Its abun-

dance fluctuated strongly through time and facies. Its fos-

sils occur most commonly in cephalopod limestone facies,

but also in other principal facies, such as shallow water

brachiopod limestones or deeper water shales, which

shows that populations of Sphooceras also inhabited oxy-

genated environments below wave base. Its presence in

anoxic deeper water facies (e.g. graptolite shale) is strongly

limited (Turek 1983, Manda 1996). In some places,

Sphooceras became one of the most numerous species in

cephalopod assemblages. Nevertheless, assemblages with

very common Sphooceras occur in various environmental

settings. The species is common (17% of collected cepha-

lopods) in the early Homerian (Wenlock) sediments, in a

thin cephalopod limestone bed, embedded in anoxic shales

in Praha-Řeporyje, Arethusina Gorge. In this case, the pop-

ulation of invertebrates inhabited deeper water, during a

short time span, when currents oxygenated the sea floor. In

the early Ludfordian (early S. linearis Zone, Ludlow),

Sphooceras occurs commonly (25% of collected cephalo-

pods) in thin cephalopod limestone beds above shales/

mudstones and below thick grainstone banks (Mušlovka

and Požáry quarries). In this case, the cephalopod lime-

stones were deposited by currents active during earlier

Ludfordian shallowing. The late S. linearis biozone (Zadní

Kopanina, Draská Gorge locality) contains a slightly youn-

ger cephalopod limestone assemblage with abundant

Sphooceras (20% of collected cephalopods, but with local

accumulations in some thin beds). In this locality, the

cephalopod limestone is rich in brachiopods, trilobites and

gastropods; even tabulate corals are occasionally present.

Although the rock is strongly dolomitized, the abundant

benthic fauna indicates a deposition directly below the fair

weather wave base, in very shallow water (to the SW, the

cephalopod limestone passes into shallow water crinoidal

grainstone).

Explaining this distribution pattern is difficult, espe-

cially since cephalopod shells are easily transported, some-

times over large distances. Usually, certain cephalopod

species were fixed to an environmental setting and depth

zone. Pelagic cephalopods are an exception, although their

abundace increases toward open-sea facies (Fig. 23). The

mosaic character of Sphooceras populations indicates

strongly varying abundance – a distribution pattern some-

what resembling that of certain modern nektonic coleoids.

The distribution pattern supports the recent conclusion that

Sphooceras was an opportunistic active swimmer. Empty

cephalopod shells served as suitable substrate for the at-

tachment of epibenthic organisms, although epizoans

rarely settled on shells of Sphooceras. Post-mortem colo-

nisation with discoidal bryozoan colonies has been found

in only two specimens. The finding of a complete exo-

skeleton of a Ludfordian trilobite Encrinuraspis beaumonti

inaSphooceras body chamber was used to support the

moulting-refuge hypothesis, i.e., the use of empty

cephalopod shells as a hiding place during trilobite moult-

ing (Davis et al. 2001).

Systematic part

Class Cephalopoda Cuvier, 1797

Angusteradulata Lehmann, 1967

Discussion. – Despite the fact that many new data concer-

ning morphology, ecology, evolution, stratigraphic range

and geographic distribution of Palaeozoic cephalopods

have been accumulated since 1950, the classification of Pa-

laeozoic cephalopods still rests strictly on morphological

798

Figure 18. A limestone sample with Sphooceras. Ludlow, early Lud-

fordian, Saetograptus linearis Zone; Zadní Kopanina, Draská Gorge;

Kopanina Formation, × 0.9. The sample contains five different growth

stages of Sphooceras truncatum (Barrande, 1860).

Bulletin of Geosciences  Vol. 87, 4, 2012

features. As the disparity and taxonomic value of these fea-

tures have been understood differently by different aut-

hors, their approaches to classification of cephalopods

have been quite varied. No consensus has been reached

concerning the number of orders and subclasses, and their

classification is therefore unsettled. Achieving a relatively

stable state of classification in this macrosystem will de-

pend not only on morphology, but also on evaluation of the

disparity of morphological features and interpretation of

the functional significance of this disparity (Barskov et al.

2008). However, to recognize the major evolutionary pat-

terns in non-ammonoid cephalopods, more intensive stu-

dies of their early ontogeny is necessary.

Systematic position and classification of straight-

shelled cephalopods with lamellar and pouch-like cameral

deposits has long been a matter of discussion, and many

discrepancies have appeared. Three main concepts have

been published, although none have been widely accepted:

Starobogatov (1974) proposed the suborder Lituitida,

which Dzik (1984) accepted and he added the suborder

Lituitina; Marek (1998) introduced the order Palliocerida

and Zhuravleva & Doguzhaeva (2004) created the

superorder Astrovioidea.

All these high-rank taxa are based on a similar pre-

sumption – the homology of cameral deposits, so we will

address only one of them, the Palliocerida. Marek (1998)

proposed the new order Palliocerida for cephalopods with

indication of the primary presence of soft tissue in their

phragmocone chambers. He distinguished two groups in

this new order, according to the morphology of the cameral

mantle derived from the morphology of cameral deposits:

one with a pouch-like cameral mantle and one, in which the

mantle consisted of radially arranged lamellae. He as-

signed the family Leurocycloceratidae Sweet, 1964 to the

former and Lamellorthoceratidae Teichert, 1961 to the lat-

ter. One of the most important diagnostic features for

Marek’s new Palliocerida order is the presence of connect-

ing rings with wide openings, so that internal space of the

siphuncle is joined with the cameral space. However,

Kolebaba (1999, 2002) documented a gradual opening of

the siphuncle during ontogeny and the existence of con-

necting rings with both dorsal openings and no openings

(tubular rings) within one specimen. Although he amended

Marek’s diagnosis of Palliocerida (Kolebaba 2002, p. 184),

he noted that re-evaluation of this order would probably be

necessary.

As opposed to the above-mentioned groups, Sphoo-

ceras is assigned here to cephalopods, in which the inter-

connection of the siphuncle and a single phragmocone

chamber prior to truncation has been well documented.

Interconection of only one segment of siphuncle with the

first phragmocone chamber is the unique feature occur-

ring in no other group of cephalopods. Discovery of

episeptal and hyposeptal deposits in the centre of the

phragmocone in one specimen only might be important

(presuming it represents no anomally) and indicates that

the taxonomic value of cameral deposits should be as-

sessed carefully.

Based on the study of internal structures of some

Palaeozoic orthocone cephalopods with so-called cameral

mantle, Zhuravleva & Doguzhaeva (2002) established the

new superorder Astrovioidea. Contrary to other cepha-

lopod workers (e.g. Teichert 1961, Bandel & Stanley 1989,

Dzik 1984, Kolebaba 1999a, b), Zhuravleva & Dogu-

zhaeva (2002) made a big account of minor differences in

morphology and structure of cameral deposits (see, e.g.,

the discussion of Lamellorthoceras or Plagiostomoceras).

Their interpretation of some structures is questionable and

they place undue emphasis on the taxonomic value of

those. Structure and character of cameral deposits is an im-

portant anatomical feature, but we do not share the opinion

that its taxonomical importance is sufficient to warrant es-

tablishing a new taxonomic unit at the level of orders (see

also Barskov et al. 2008). The crucial problem of all the

above-mentioned concepts is their fixation on the structure

of cameral deposits. Cambrian cephalopods have empty

phragmocone chambers. Consequently, there is no evi-

dence of homology of lamellar deposits in different groups

799

Figure 19. Early ontogeny of Sphooceras. Due repeated process of

truncation the earliest growth stage cannot be assigned to this genus un-

equivocally. Based on specimens illustrated in Fig. 15F, J. Scale bar is

5 mm.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

of cephalopods, and cameral deposits were developed

convergently. In any case, the construction and function of

endocameral as well as endosiphuncular deposits must be

better understood prior to its application to higher rank sys-

tematics.

A useful indicator of higher-level cephalopod classifica-

tion is the morphology of embryonic shells. In straight-

shelled cephalopods, there are substantial differences in the

morphology of their embryonic shells, and these differences

are much more distinct than in nautiloids. Embryonic shells

thus provide a good basis for classification of straight-

shelled cephalopods, and it may even be possible to split

them into more orders. However, this depends on the corre-

lation of juvenile shells with adult shells, so basically the

entire ontogeny has to be known. Orthoceras and

Michelinoceras, both typical orthocerids, have a sub-

spherical protoconch lacking a cicatrix with either a very

gentle constriction at the base (Orthoceras, see Balashov

1957), or no constriction at all (Michelinoceras, Serpagli &

Gnoli 1977). The oldest known orthocerid Bactroceras has

an embryonic shell similar to Michelinoceras (Evans 2005).

A small spherical protoconch without cicatrix, distinct

constriction and later rapidly expanding embryonic shell

may be an indicator for classifying cephalopods at a sys-

tematic level higher than family. Similarities between em-

bryonic shells in the discussed straight-shelled cephalo-

pods and in bactritoids, ammonoids and belemnites are

evident. Sphooceras most probably had such a spherical

apex and consequently, its position in the Orthocerida

is questionable, but more data is needed in order to solve

higher-level classification of cephalopods with straight

shells and lamellar deposits. To express our interpretation

about the closer relationship of Sphooceras with coleoids

than to nautiloids, we assign this genus to Angusteradulata,

group including bactritoids, ammonoids and coleoids also

some orthocerids (Engesser 1996).

Cameral deposits limited to a single chamber and the

periodic truncation process are unique and derived features

of Sphooceras. Its early growth stage morphology and

lamellar cameral deposits strongly resemble those of the

Silurian Plagiostomoceras Teichert & Glenister, 1952 and

Murchisoniceras Babin, 1966. Both these cephalopods

have longicone shells and well developed cameral depos-

its. The process of truncation is not yet well documented in

these genera, but Barrande assumed it in Plagiostomoceras

as early as 1860. Truncation appears probable in

Plagiostomoceras endymion (Barrande, 1867) from the

late Wenlock and earlier Ludlow of Bohemia. Shells of

Plagiostomoceras and Murchisoniceras are very slowly

expending (Barrande 1868, 1870) and their length would

likely have caused difficulties in maneuvering. Reduction

of shell length through periodic truncation would have con-

siderably reduced such problems. Vascular imprints on

the surface of cameral deposits strongly resemble similar

mantle imprints described in Silurian Leurocycloceras

(Flower 1941, Holland 1964).

Family Sphooceratidae Flower, 1962

Discussion. – Gnoli & Kiselev (1994) divided the family

into two subfamilies, Sphooceratinae and Disjunctocerati-

nae. The former contains only Sphooceras and the latter

contains Disjunctoceras and Andigenoceras, both lacking

a callus in the posterior portion of the shell. We consider

Disjunctoceras and Andigenoceras to be synonymous with

Sphooceras and thus the division of Sphooceratidae into

subfamilies superfluous (see following discussion).

Genera included. – Sphooceras Flower, 1962.

Genus Sphooceras Flower, 1962

[Synonymy: Andigenoceras Gnoli in Kiselev, 1992, Dis-

junctoceras Gnoli in Kiselev, 1992]

Type species. –Orthoceras truncatum Barrande, 1860; Ko-

panina Formation; Silurian, Ludlow, Gorstian, Neodiver-

sograptus nilssoni Zone; Praha-Butovice (“Butowitz”).

Amended diagnosis (cf. Kröger 2005). – Shell is straight,

short, very slowly expanding; in fully-grown specimens,

apical angle at midpoint of body chamber is frequently

slightly decreasing. Body chamber is 1.5–3 times longer

than phragmocone, which has at most seven or eight short

or moderately long chambers. Sutures are transversal or

slightly oblique to shell axis. Apex with plugged siphonal

opening is bluntly rounded; viewed laterally, ventral side is

more convex than dorsal. In median section, apex is mar-

kedly thickened owing to episeptal deposits forming a cal-

lus; one or two additional layers form an outer cover – an

inner one with roughly concentric wrinkles (fingerprint

pattern) and an outer layer, which is smooth and very thin.

Siphuncle moderately wide, shifted slightly ventrally from

the centre. Siphonal necks are orthochoanitic to cyrtoto-

choanitic. Surface of shell is usually entirely smooth or

with slightly expressed growth lines laterally oblique to

shell axis, delimiting a wide hyponomic sinus. Dorsally si-

tuated retractor muscle scars fused into single lobe. Colour

pattern forms longitudinal stripes on dorsal side. Proto-

conch small, probably subglobular.

Discussion. – Kröger (2008, p. 55), following up on the ge-

neric diagnosis of the Sphooceras by Sweet (1964), publis-

hed an amended diagnosis, partially based on new speci-

mens from Morocco. However, these specimens are not

well preserved, as he himself mentioned, so their assign-

ment to Sphooceras is questionable. The most problematic

800

Bulletin of Geosciences  Vol. 87, 4, 2012

structures are cameral and epichoanitic deposits, precipita-

tion of which, as mentioned by Kröger (2008), could be

post-mortem. No similar deposits have been found in any

of the numerous well-preserved specimens of Sphooceras

from Bohemia or Gotland. Therefore, these features cannot

be accepted as diagnostic. Kröger’s superposition of layers

801

Figure 20. Sphooceras truncatum Barrande, 1860; Ludlow, Kopanina Formation, Zadní Kopanina, Bohemia. Internal structures in the first

phragmocone chamber showing replica of cameral tissue. • A–D – specimen NM L 9181 illustrated by Barrande (1868, pl. 341, figs 6–10); for explana-

tion of individual shell structures compare Fig. 1B in this paper. Ventral, dorsal and lateral views; × 4.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

forming the apex of the shell is reversed, and phragmocone

chambers with highly variable convexity are generally

short. Deciduous portions of the conch, so far reported

as unknown, actually occur together with complete ones

rather frequently.

Erection of the two new genera Disjunctoceras Gnoli in

Kiselev, 1992 as well as Andigenoceras Gnoli in Kiselev,

1992 and classifying them within Sphooceratidae has sig-

nificantly changed the content of this originally mono-

generic family. During our study of Sphooceras truncatum,

the specimens assigned to Disjunctoceras disjunctum were

also examined. According to Gnoli & Kiselev (1994),

Disjunctoceras disjunctum “differs substantially from

S. truncatum in the presence of recumbent septal necks and

the absence of a terminal callus”. However, the single lon-

gitudinally cut specimen (NM L 17550), showing internal

structures and studied by Gnoli is in fact incomplete. It has

three phragmocone chambers adjacent to the body cham-

ber. The apical part, preserved as an internal mould is not

cut exactly in the median plane and the specimen is com-

pletely exfoliated, so it would have been impossible for

Gnoli to have seen any traces of the siphuncle and callus.

Several other specimens of “O.”disjunctum have been re-

cently cut in the medium plane, and three of them have very

well preserved internal structures, showing a terminal cal-

lus. The lectotype (NM L 17549) shows the outer surface

of the shell in the apical region. It has three phragmocone

chambers, i.e. the minimum number supposed. The short

and fine longitudinal striae, commonly observed in Sphoo-

ceras, are recognizable around the entire circumference of

the base of the first chamber. This feature characterises the

surface of the apical callus in Sphooceras, confirming the

existence of slightly developed cameral deposits. Except

for the plugged siphuncle, the convex adapical region of

the shell is smooth.

The other feature separating Disjunctoceras and

Sphooceras is the more flared (suborthochoanitic to

cyrtochoanitic) septal necks (Gnoli & Kiselev 1994). How-

ever, the variety of septal necks in Sphooceras is remark-

able, often even within one specimen. For instance, in the

specimen NM L 9199 (Barrande 1868, pl. 343, fig. 15), the

septal necks are orthochoanitic in the first chamber but

suborthochoanitic in the others. In “O.”disjunctum, they

are subortochoanitic to cyrtochoanitic. Sphooceras exhib-

its a fairly strong inverse correlation between the length of

phragmocone chambers and flaring of the septal necks.

Variation in septal neck shapes in the Sphooceratidae is not

important enough to warrant classification into separate

genera. We therefore assign both species “D.”disjunctum

and S. truncatum to the single genus Sphooceras.

Manda & Kříž (2007, p. 40, fig. 5) tentatively attributed

the poorly known species Orthoceras sacculus Barrande,

1860 from the Gorstian (L. scanicus Biozone) to Sphoo-

ceras. However, this assignment has not been confirmed.

Sphooceras amplum Kiselev, 1968 in Balashov &

Kiselev (1968, pl. 1, fig. 5) from the late Silurian of Podolia

exhibits a slowly expanding longicone shell with widely

spaced septa and a relatively thick subcentral siphuncle,

with moderately vaulted connecting rings. These features

clearly illustrate that this species does not belong to

Sphooceras.

Orthoceras sarcinatum Barrande, 1868 was described

based on two specimens, but only one, from Butovitz e1 lo-

cality bas been illustrated (Barrande 1868, pl. 341, figs 19,

20, holotype by monotypy NM L 17531). This species is

reassigned here to Sphooceras truncatum.

Disjunctoceras shurabense Kiselev, 1992 from the late

Wenlock and early Ludlow of Tian-Shan also actually be-

longs to Sphooceras, but this species is poorly known. It

differs from Sphooceras truncatum in having a greater an-

gle of shell expansion (Kiselev et al. 1993).

Sphooceras furmanense Kiselev, 1992 from the early

Wenlock, Podoli in Ukraine, was insufficiently illustrated

and thus the position of this species remains questionable,

and it may be considered a nomen dubium.

Dzik (1984, p. 135) suggested that Hirnantian species

“Ecdyceras”foerstei Flower, 1946 from Kentucky could

be assigned to Sphooceras, but this species does not exhibit

any diagnostic feature of Sphooceras.

Species included.–Sphooceras truncatum (Barrande,

1860); Sphooceras disjunctum (Barrande, 1860); stratigrap-

hic range and geographic distribution – see below; Sphoo-

ceras shurabense (Kiselev, 1992), late Wenlock and early

Ludlow of Tian-Shan; Sphooceras andigense (Kiselev,

1992), Přídolí, Tian-Sha; Sphooceras furmanense Kiselev,

1992, early Wenlock, Podoli in Ukraine.

Sphooceras truncatum (Barrande, 1860)

Figures 2–5, 9–11, 13C, 14–20

1855 Orthoceras truncatum (nom. nud.). Barrande, p. 280.

1860 Orthoceras truncatum (n. sp.); Barrande, pp. 573–600,

pl. 9, figs 1–20.

1868 Orthoceras truncatum Barrande. – Barrande; pl. 342,

figs 1–20, pl. 344, figs 1–6.

1868 Orthoceras sarcinatum Barrande; Barrande, pl. 341,

figs 19, 20.

1868 Orthoceras apperiens Barrande. – Barrande, pl. 344,

figs 19–21.

1870 Orthoceras truncatum Barrande. – Barrande, pl. 448,

figs 3–5.

1874 Orthoceras truncatum Barrande. – Barrande,

pp. 556–559.

1882 Orthoceras truncatum Barrande, 1860. – Blake,

p. 151, pl. 14, fig. 8.

1888 Orthoceras truncatum Barrande. – Foord, pp. 23–26.

802

Bulletin of Geosciences  Vol. 87, 4, 2012

1888 Orthoceras truncatum Barrande. – Schröder, p. 220.

1925 Orthoceras truncatum Barr. – Heller, p. 245, pl. 3,

fig. 19.

1929 Orthoceras truncatum Barrande, 1860. – Heritsch,

p. 67, pl. 7, figs 684, 685.

1941 Orthoceras truncatum Barrande. – Flower, pp. 473,

474.

1955 Orthoceras truncatum Barrande. – Flower, p. 100.

1955 “Orthoceras” truncatum Barrande. – Flower, p. 860.

1962 Orthoceras truncatum Barrande. – Furnish et al.,

p. 1344.

1963 Sphooceras truncatum (Barrande). – Flower, p. 95.

1964 Sphooceras truncatum (Barrande). – Sweet,

pp. K231/2, fig. 156A5.

1975 Sphooceras truncatum (Barrande). – Balashov,

pp. 81–85, pl. 3, fig. 5.

1978 Sphooceras truncatum (Barrande). – Zhuravleva, p. 19.

1984 Sphooceras truncatum (Barrande, 1860). – Dzik,

pp. 112, 135, 138, pl. 31, figs 5–7, text-figs 42.19,

55.35.

1986 Sphooceras truncatum (Barrande). – Turek & Marek,

pp. 240, 252, fig. 3.1–9.

1987 Sphooceras truncatum (Barrande). – Kiselev et al.,

p. 50, pl. 13, fig. 4.

1990 Sphooceras truncatum (Barrande). – Gnoli, pp. 302,

304, pl. 4, fig. 2a–5.

1991 Sphooceras truncatum (Barrande). – Gnoli & Ser-

pagli, pp. 188, 194, pl. 1, fig. 7.

1992 Sphooceras truncatum (Barrande). – Kříž, p. 104,

pl. 1, fig. 24.

1992 Sphooceras truncatum (Barrande). – Kiselev, p. 16.

1993 Sphooceras truncatum (Barrande, 1860). – Kiselev et

al., p. 55, pl. 11, fig. 5.

cf. 1994 Sphooceras truncatum (Barr.). – Kiselev & Modza-

levskaya, p. 84.

1994 Sphooceras truncatum (Barrande). – Gnoli & Kise-

lev, pp. 416/7, text-figs 1a–c.

non 2008 Sphooceras truncatum (Barrande, 1860). – Kröger,

p. 56, pl. 6, fig. 2, pl. 11, fig. 2 (= ?Plagiostomoceras

sp.).

Diagnosis. – Type species of Sphooceras Barrande (1860),

whose shell, with 7 or 8 phragmocone chambers, could at-

tain lengths up to 30 cm, with dorsoventral diameter up to

90 mm. Apical angle in the midpoint of the body chamber

in fully-grown specimens is usually slightly decreasing.

Cameral deposits forming the apical callus are relatively

thick in mature specimens and almost fill the first phragmo-

cone chamber, subsequently covered by two outer layers.

The inner one has roughly concentric wrinkles (fingerprint

pattern) and the outer layer is smooth. The siphuncle has

orthochoanitic to suborthochoanitic siphonal necks.

803

Figure 21. Schematic drawing of Sphooceras ontogeny, showing selected phases of growth. 1 – egg containing embryo, freshly hatched embryo and ju-

venile executing first truncation; 2 – young growth stage with relatively long phragmocone, just before and during truncation process; 3 – specimen after

truncation with only four phragmocone chambers and thin apical callus; 4 – immature specimen during truncation showing “naked” cameral deposits

forming new apex; mantle is withdrawn into body chamber; truncated part of phragmocone (four chambers) with partially removed outer shell-wall

shows thick cameral deposits; 5 – adult specimen covered by mantle extended from aperture. Shell slightly narrowing to aperture, cameral deposits thick,

last septa narrowly spaced.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Remarks. – Barrande (1860, 1868) gave special attention to

the species “Orthoceras”truncatum. Type and additional

specimens were carefully selected and precisely illustrated

on several plates. He recognized the high variability within

this species. Barrande expressed the detection of differen-

ces in the morphology of these specimens by distinguis-

hing two varieties: O. truncatum var. index and O. trunca-

tum var. perornata. We suppose these forms to be only

morphs within the populations falling into intraspecific va-

riability. Barrande’s concept of the species O. truncatum

corresponds with our view.

All newly described features (colour pattern, muscle

scars, occasional cameral deposits in addition to the apical

callus, embryonic shell presumably of S. truncatum) have

been discussed above in the section concerning morphol-

ogy.

Occurrence. – Central Bohemia (Barrandian, Prague Ba-

sin).

Motol Formation, Wenlock, Homerian; C. lundgreni

Zone, T. testis Subzone: Butovice, Kační Quarry; Lištice

Herinky, Barrande’s pits; Lištice U cestičky section No.

759, bed No. 3; Praha-Velká Ohrada, Arethusinová Gorge

section No. 687; Kosov Quarry near Beroun, new quarry,

6th level, section No. 767; Tachlovice, Prostřední Mill.

M. ludensis Zone: Praha-Bráník, Školní vrch, section

No. 764, bed No. 8.

Kopanina Formation, Ludlow, Gorstian. N. nilssoni

Zone: Praha-Butovice, Na břekvici section 584, bed Nos.

10 and 11; Praha-Butovice, road cut to Hemrovy Rocks;

Praha-Lochkov, field E of the village (nodules from field);

Tachlovice, Prostřední Mill.

L. scanicus Zone: Kosov near Beroun, new quarry, top

of western wall above pool and section No. 780; Praha-

Braník, Školní vrch; Praha-Reporyje, roadcut to W of vil-

lage; Praha-Malá Chuchle, Vyskočilka Hillside, bed No. 6;

Praha-Velká Ohrada, Cromus Hillside; Sedlec, Barrande’s

pits, bed No. 3.

Early S. linearis Zone: Kosov near Beroun, section No.

780; Praha-Velká Ohrada, Mušlovka Quarry; Praha-Ře-

poryje, Požáry Quarry.

Late S. linearis Zone: Dlouhá hora near Beroun,

U lanovky section; Kosov Quarry near Beroun, section

780; Praha-Lochkov, Barrande’s pits; Praha-Lochkov,

Nad ubikacemi; Praha-Řeporyje, Požáry Quarry, bed No.

1; Praha-Řeporyje, Marble Quarry, beds No. 1 and 2;

Praha-Velká Ohrada, Mušlovka Quarry, bed Nos 1 and 2;

Praha-Zadní Kopanina, Nad Jirasovým lomem section

887, bed No. 3 (lower part); Praha-Zadní Kopanina,

Draská Gorge; Velký vrch near Koněprusy.

B. bohemicus and N. inexpectatus zones: Praha-

Lochkov, Marble Quarry and Barrande’s pits; Praha-Velká

Ohrada, Mušlovka Quarry; Praha-Zadní Kopanina, Nad

Jirasovým lomem section; Kosov Quarry near Beroun, sec-

tion Nos. 418, 772.

N. kozlowskii Zone: Praha-Lochkov, Marble Quarry

and Barrande’s pits, Nad ubikacemi section; Praha-

Slivenec, old quarry; Praha-Velká Ohrada, Mušlovka

804

Figure 22. Distribution of Sphooceras and reconstruction of oceanic currents (Wilde et al. 1991) and distribution of warm, temperate and cool water

masses. For data see the text. Palaeogeographic reconstruction of the Wenlock based on the Paleomap Project of C.R. Scotese, Perunica microplate posi-

tion after Cocks & Torsvik (2002).

Bulletin of Geosciences  Vol. 87, 4, 2012

Quarry; Praha-Nová Ves, Pod Hradištěm I, II, III;

Praha-Řeporyje, Požáry Quarry; Praha-Zadní Kopanina,

Nad Jirasovým lomem section.

Latest N. kozlowskii Zone: Koněprusy, Velký vrch, sec-

tion 913, bed No. 5; Kosov near Beroun, section No. 782

(bed No. 22/23) and section No. 924 (bed No. 13); Praha-

Lochkov, Marble Quarry; Praha-Nová Ves, Pod Hradištěm

II, bed No. 13; Praha-Zadní Kopanina, Nad Jirasovým

lomem section, bed No. 5.

Ps. latilobus-S. balticus Zone: Praha-Lochkov, Bar-

rande’s pits; Praha-Kosoř, old quarry; Praha-Lochkov, Mar-

ble Quarry; Praha-Lochkov, Nad ubikacemi section; Praha-

Malá Chuchle, Vyskočilka; Praha-Pankrác, Sdružení.

M. fragmentalis Zone: Praha-Lochkov, Barrande’s

pits; Praha-Lochkov, Nad ubikacemi section; Praha-

Dvorce, Podolí.

P. parultimus Zone: Praha-Lochkov, Nad ubikacemi

section.

In addition to the Prague Basin, Sphooceras truncatum

occurs in Elbersreuth, Germany (Heller 1925), Gotland,

Sweden (Dzik 1984), Carnic Alps, Austria (Histon 1999),

Montagne Noire and Calvados, France, south-west Sar-

dinia, Italia (Histon & Gnoli 1999, Gnoli 2003), Poland

(Dzik 1984), Podoli, Ukraine (Kiselev et al. 1987, Kiselev

1995), England (Blake 1882), ?Bardymsk Formation,

early–middle Ludfordian, Ufimskij Amfiteatr (Kiselev &

Modzalevskaya 1994), and Tian-Shian, Kazachstan

(Kiselev & Starshinin 1987).

Sphooceras disjunctum (Barrande, 1868)

Figures 7, 8, 12, 13A, B, D, E

1860 Orthoceras disjunctum Barr. (nomen nudum). – Bar-

rande, p. 588.

1868 Orthoceras disjunctum Barr.; Barrande, pl. 345,

figs 8–12.

1874 Orthoceras disjunctum; Barrande, p. 631.

1888 Orthoceras disjunctum Barrande. – Foord, p. 27.

1888 Orthoceras disjunctum Barrande. – Schröder, p. 228.

1992 Disjunctoceras disjunctum (Barrande). – Kiselev,

p. 17.

1994 Disjunctoceras disjunctum (Barrande). – Gnoli & Ki-

selev, pp. 417, 418, text-figs 2a–c.

805

Figure 23. Distribution of Sphooceras in dependence on facies in the Silurian of the Prague Basin. Light gray infill indicates rare occurrence, medium

gray infill common occurrence, dark-gray infill indicate very common or mass occurence.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Diagnosis.–Sphooceras with very short shell, three to

five short phragmocone chambers. Body chamber may be

almost three times longer than phragmocone. Shell thin

walled, with markedly thickened peristome (constriction

visible on internal mould). Apex thickened owing to pre-

sence of thin apical callus, massive deposits inside the first

chamber not developed. Sutures almost perpendicular to

the shell axes, siphonal necks suborthochoanitic or even

cyrthochoanitic.

Occurrence. – Central Bohemia (Barrandian, Prague Basin).

Motol Formation, Wenlock, Homerian; C. lundgreni Zone,

T. testis Subzone: Butovice, Kační Quarry. Kopanina For-

mation, Ludlow, Gorstian; N. nilssoni Zone: Praha-

Butovice, Na břekvici section; Řeporyje. L. scanicus Zone:

Praha-Malá Chuchle, Vyskočilka Hillside, bed No. 6.

Conclusions

Sphooceras is still the only known Early Palaeozoic cepha-

lopod in which temporary complete encasing of the shell

by mantle extended from the body chamber has been sug-

gested. It was linked with the periodic natural truncation of

the apical part of the phragmocone (3 to 5 chambers), a pro-

cess that has been unequivocally documented. Therefore,

throughout ontogeny, the shell was short and the length of

the body chamber was one and half or even three times the

length of the phragmocone. Temporary complete encasing

of the shell by mantle is here suggested because of the pre-

sence of two calcareous layers secreted on the surface of

the apical callus – exposed episeptal deposits including

structurally reworked septum – which formed the apical

part of the shell subsequent to truncation. The inner layer

bears a characteristic fingerprint pattern (in S. truncatum)

and the very thin, smooth outer layer shows a colour pat-

tern. Longitudinal stripes running radially from the cir-

cumference of the plugged siphuncle are present only dor-

sally; the ventral side was unpigmented. The presence of

colour stripes in this region serves as additional indication

that the shell of this nautiloid was periodically completely

covered by the mantle, an organ containing pigment cells

secreting colour patterns in molluscs.

The colour pattern documents that these layers could not

have been secreted by long arms (cf. Barrande 1860), nor a

hood (Hyatt 1883–1884) nor a siphon-cameral tissue (cf.

Gnoli & Kiselev 1994). A new idea is given here for the pro-

cesses preceding truncation and subsequent completion of

the new apex. A remarkable feature, documented especially

in Sphooceras disjunctum, is an extremely thin shell wall in

the apertural region. It would not have been able to with-

stand wave action in the shallow water environment inhab-

ited by the animal without being protected by the soft tissue

– another indication of covering of the shell by the mantle.

Affinity of some Early Palaeozoic straight-shelled ce-

phalopods to coleoids has been already indicated, espe-

806

Figure 24. Stratigraphic range and latitudinal distribution of Sphooceras species. Light gray colored lines indicate uncertain stratigraphic ranges. For

data see systematic part. Aval. Means Avalonia.

Bulletin of Geosciences  Vol. 87, 4, 2012

cially by finds in orthocerids of coleoid type of radula

(Mehl 1984, Gabbot 1999); reported traces of ten tentacles

(Flower 1955b, Stürmer 1985) has been, however,

doubted. A “semi-internal” shell of Sphooceras tempo-

rarily completely encased by soft tissue, reduction of the

length of the phragmocone, shortening of the shell accom-

panied by relative prolongation of body chamber possess-

ing oblique aperture, dorsally situated retractor muscle im-

prints, probably very small subglobular protoconch lacking

cicatrix, noncalcified connecting rings and hydrodynamic

shape of the shell are all features, which evolved in the ge-

nus Sphooceras in convergence to the Angusteradulata.

Sphooceras, however, lacks some important coleoid fea-

tures such as a rostrum-like shell deposited on a signifi-

cant portion of the outside, a ventral siphuncle with more

or less straight connecting rings as well as the characteris-

tic sinuses and projections of the aperture (proostracum

etc.). On the other hand there is extreme disparity of

septal neck shapes in Carboniferous coleoids. In some

oldest coleoids connecting rings expanded within

phragmocone chambers. In Rhiphaeoteutethis there are

suborthochoanitic septal necks and the siphuncle could

not be simply tubular, also in Hematites connecting rings

were very probably inflated, similarly as in Sphooceras

(see Doguzhayeva et al. 2010). Also proostracum-like

structures are missing in some of these coleoids, e.g.in

Donovaniconida and Hematitida.

The character of truncation in Sphooceras may be

viewed as a case of autapomorphy, a progressive evolu-

tionary experiment appearing as early as in Silurian cepha-

lopods, indicating some parallels with coleoids. The mode

of shell repair in Sphooceras differs significantly from that

in other nautiloids in which truncation has been reported,

as well as from some gastropods in which it occurs more

frequently.

The shell of Sphooceras was highly variable both in

outer morphology (shape, surface sculpture) and internal

structures (convexity of septa, their orientation to the shell

axis, shape of siphonal necks), and the occasional presence

of massive cameral deposits in an additional phragmocone

chamber besides the first one. A qualitative analysis of

shell variability in Sphooceras supports that it is the only

known genus of the Sphooceratidae family; we consider

the genera Disjunctoceras Gnoli & Kiselev and Andigeno-

ceras Kiselev synonyms of Sphooceras.

Sphooceras, probably closely related to Plagio-

stomoceras,Murchisoniceras and Parasphaerorthoceras,

derives from other straight-shelled cephalopods with fully

developed cameral deposits. Due to the reduction of the

phragmocone, cameral deposits were limited to the apical

callus.

The morphology of the shell and its wide distribution in

tropical and subtropical seas of Europa and Asia indicate

that Sphooceras was an active nektonic or nectobenthonic

animal with neutral buoyancy, keeping its body horizontal.

Musculature of the mantle and hyponome probably en-

abled effective swimming.

Acknowledgments

This research was supported by the Czech Grant Agency

through the project GACR 2005/09/0260 (VT) and GACR

205/09/0703 (ŠM). The authors thank Fred Collier and Jessica

Cundiff (Museum of Comparative Zoology, Harvard), Jan

Bergström and Jonas Hagström (Swedish Museum of Natural

History, Stockholm), Melissa Claire (Museum of Natural His-

tory, London) for providing the material used in this study and

other great help during our stay in the mentioned institutions,

Christian Klug (Paläontologisches Institut und Museum,

Universität Zürich) and David Evans (Natural England,

Peterborough) for very helpful comments, Petr Daneš, Prague

and Ronald Parsley (Tulane University, New Orleans) for im-

proving English and valuable discussions, and Ivan Kolebaba

(Zdice) for technical help and drawings.

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Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

812

Appendix 1

Graphs showing changes in phragmocone chamber lengths during ontogeny in Sphooceras truncatum. All measurements based on

813

specimens cut in median plane; bc means that body chamber is preserved. Phragmocone chambers numbered along x-axis, from sep-

tum truncation (oldest still-attached chamber) toward aperture, y-axis shows length of each chamber in mm. For data see Table 1.

Appendix 2

Graphs showing changes in phragmocone chamber length during ontogeny in Sphooceras disjunctum. All measurements based on speci-

mens cut in median plane; bc means that body chamber is preserved. Phragmocone chambers numbered along x-axis, from septum trun-

cation (oldest still-attached chamber) toward aperture, y-axis shows length of each chamber in mm. For data see Table 2.

Vojtìch Turek & tìpán Manda  An endocochleate experiment in the Silurian straight-shelled cephalopod Sphooceras

Lituitid cephalopods from the upper Darriwilian and basal Sandbian (Middle–Upper Ordovician) of Estonia

Article

Jul 2020

Cephalopods of the order Lituitida Starobogatov, 1983 from the late Darriwilian and early Sandbian strata of Estonia are revised herein. During that time, the lituitids reached their peak abundance and were among the key components of cephalopod faunas on Baltica, as well as in other mid- and low-latitude palaeogeographic locations. The Estonian lituitids mostly come from localities representing more off-shore environments with deeper-water sedimentation in the Middle Ordovician. This supports previous assumptions that lituitids preferred pelagic environments and were capable of long-distance migration. In the studied lituitid collection, two genera were identified – Lituites Bertrand, 1763 and Ancistroceras Boll, 1857. Three species – Ancistroceras ristnensis sp. nov., Ancistroceras vahikuelaensis sp. nov. and Lituites nehatuensis sp. nov. – were newly established. However, species determinations were often hindered by high intraspecific variability and fragmentary preservation. Investigation of cameral deposits using median sections showed that: connecting rings in chambers with deposits are commonly broken or missing; oriented fragments of connecting rings are present, sometimes overgrown by primary deposits; several generations of primary deposits can be developed; simultaneous presence of both broken and intact connecting rings in the same specimen is usual. These observations elucidate the formation of cameral deposits in lituitids. Currently, this process is explained either by passive deposition from cameral fluids, or active secretion by cameral mantle. The evidence collected herein from Estonian lituitids reveals, however, that both modes of formation might have occurred successively during the lituitid ontogeny and that a gradual, life-time destruction of connecting rings was possibly involved.

High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K

Article

Mar 2019

High-level classification of the nautiloid cephalopods has been largely neglected since the publication of the Russian and American treatises in the early 1960s. Although there is broad general agreement amongst specialists regarding the status of nautiloid orders, there is no real consensus or consistent approach regarding higher ranks and an array of superorders utilising various morphological features has been proposed. With work now commencing on the revision of the Treatise Part K, there is an urgent need for a methodical and standardised approach to the high-level classification of the nautiloids. The scheme proposed here utilizes the form of muscle attachment scars as a diagnostic feature at subclass level; other features (including siphuncular structures and cameral deposits) are employed at ordinal level. We recognise five subclasses of nautiloid cephalopods (Plectronoceratia, Multiceratia, Tarphyceratia nov., Orthoceratia, Nautilia) and 18 orders including the Order Rioceratida nov. which contains the new family Bactroceratidae. This scheme has the advantage of relative simplicity (it avoids the use of superorders) and presents a balanced approach which reflects the considerable morphological diversity and phylogenetic longevity of the nautiloids in comparison with the ammonoid and coleoid cephalopods. To avoid potential confusion arising in the higher levels of nautiloid classification employed in the revision of the Treatise Part K, we propose herein to replace the suffix ‘-oidea’ at subclass level with the suffix ‘-ia’. Apart from removing ambiguity and clarifying the nomenclature, this approach also brings greater consistency and affinity with modern zoological classification schemes used for cephalopods. The original Treatise Part K adopted an ‘abbreviated’ form of name for nautiloid orders using the ending ‘-cerida’ rather than ‘-ceratida’ (e.g., Order Actinocerida rather than Actinoceratida). For the revision of Treatise Part K, we propose using the ‘full’ version of the ordinal names. This approach re-employs several order names in their original form, e.g., Ellesmeroceratida, Oncoceratida, and Tarphyceratida. For reasons of consistency, we also apply the same to ordinal names created since the original Treatise Part K; therefore, Order Bisonocerida becomes Bisonoceratida.

Early and Middle Devonian cephalopods from Hamar Laghdad (Tafilalt, Morocco) and remarks on epicoles and cameral deposits

Article

Full-text available

Nov 2018
Neues Jahrbuch Geol Palaontol Abhand

Devonian condensed sections of the northern Tafilalt Platform (Anti-Atlas, Morocco) are often extremely rich in cephalopod associations. Here, we describe Pragian to late Givetian cephalopods from Hamar Laghdad (Tafilalt). In total, we found 44 species belonging to 32 genera. While no new species of ammonoids or bactritids were recovered, we report two new genera and eight new species of nautiloids, which have been studied much less than the other cephalopod groups in the past despite their great abundance, diversity and morphologic disparity in the eastern Anti-Atlas. The genera Mesonaedyceras and Subtheoceras are newly introduced as well as the new species Aphyctoceras friesenbichlerae, Astoceras floweri, Geidoloceras hebeiseni, Infundibuloceras kroegeri, Mesonaedyceras laterobliquum, Pachtoceras laghdadense, Pseudendoplectoceras angustum and Subtheoceras striatum. In addition, we describe exceptionally preserved three-dimensional cameral deposits of orthoconic cephalopods and several cases of post mortem epicoles on cephalopod conchs.

Recent advances in heteromorph ammonoid palaeobiology

Article

Full-text available

Jan 2021
BIOL REV

Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non-planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, hetero-morphs like other ammonoids had 10 arms, a well-developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles , a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus-type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U-shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near-neutral buoyancy regardless of conch shape or ontog-eny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near-horizontal aperture pointing upwards. Heteromorphs with a U-shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep-subtidal to offshore facies but are rare in shallow-subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep-subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow-subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro-and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinction of ammonoids. Ammonoids likely persisted after this event for 40-500 thousand years and are exclusively represented by heteromorphs. The ammonoid extinction is linked to their small hatchling sizes, planktotrophic diets, and higher metabolic rates than in nautilids, which survived the K/Pg mass extinction event.

Review of ascocerid cephalopods from the upper Silurian of the Prague Basin (Central Bohemia) – history of research and palaeobiogeographic relationships

Article

Full-text available

Aug 2019

Martina Aubrechtova

The order Ascocerida K uhn , 1949 includes rare and morphologically unique early Palaeozoic cephalopods, in which periodic shell truncation occurred during ontogeny; mature shells subsequently became inflated, with thin sigmoidal septa and phragmocone chambers situated above the living chamber. The ascocerids are at present known mainly from North America and Baltoscandic Europe. The group was first described by J. Barrande in the mid 1800’s from the upper Silurian of Bohemia. Finds of ascocerid fossils in Bohemia are generally scarce but Barrande’s collection includes tens of well-preserved specimens. These are briefly reviewed in the present paper and additional, more recently collected material is also discussed. In Bohemia (Prague Basin), ascocerids occur in limestones of Ludlow to late Přídolí age. Their maximum diversity and abundance was reached close to the Ludlow/Přídolí boundary interval. Five out of the fourteen currently recognized Bohemian species are also known from late Silurian strata in Sweden (the island of Gotland). The ascocerids thus illustrate palaeobiogeographic relationships between the Prague Basin and Baltica during the late Silurian.

Anatomy and evolution of the first Coleoidea in the Carboniferous

Article

Full-text available

Jul 2019

Coleoidea (squids and octopuses) comprise all crown group cephalopods except the Nautilida. Coleoids are characterized by internal shell (endocochleate), ink sac and arm hooks, while nautilids lack an ink sac, arm hooks, suckers, and have an external conch (ectocochleate). Differentiating between straight conical conchs (orthocones) of Palaeozoic Coleoidea and other ectocochleates is only possible when rostrum (shell covering the chambered phragmocone) and body chamber are preserved. Here, we provide information on how this internalization might have evolved. We re-examined one of the oldest coleoids, Gordoniconus beargulchensis from the Early Carboniferous of the Bear Gulch Fossil-Lagerstätte (Montana) by synchrotron, various lights and Reflectance Transformation Imaging (RTI). This revealed previously unappreciated anatomical details, on which we base evolutionary scenarios of how the internalization and other evolutionary steps in early coleoid evolution proceeded. We suggest that conch internalization happened rather suddenly including early growth stages while the ink sac evolved slightly later.

Siphonal tube structure of the Late Devonian orthocerid Dolorthoceras from the Polar Urals (NW Russia) preserving nacre and organic fibres as well as its persistence in cephalopod evolution

Article

Full-text available

Mar 2019

Larisa Doguzhaeva

A juvenile orthocerid Dolorthoceras sp. from the Frasnian (Late Devonian) of the Polar Urals in NW Russia is the first recorded ectocochleate cephalopod showing fibrous structures and the first Devonian cephalopod preserving nacreous structures within its conch. Like Nautilus, Dolorthoceras sp. has columnar nacre in its shell wall and septa, which are composed of differentiated nacreous tablets that are c. 3 lm and 10 lm in diameter. The central, small, cylindrical, hollow siphonal tube-studied in median section using scanning electron microscope-comprises short columnar-nacreous sub-orthochoanitic septal necks and thin, apparently primarily chitinous, connecting rings; swollen, lens-shaped in median section, two-part fibrous non-biomineralized structures-here named clutches-envelope the posterior parts of the septal necks. Together with the adjacent connecting ring, the outer part of the clutch may extend onto adapical septal surfaces; their inner part and adjoining from inside next connecting ring line the septal neck. The clutches are comparable, to some degree, to the auxiliary deposits and cuffs of the siphonal tubes found in ammonoids; these are interpreted as being protective structures of the conjunctions between the connecting rings and septal necks reinforcing it against hydrostatic pressure, which was probably also the case in Dolorthoceras. Tracing the Silurian to Cretaceous longiconic cephalopods with narrow, central to eccentric, hollow siphonal tubes and swollen posterior portions of the septal necks shows that the Dolorthoceras-type siphonal tube may represent a conch structure that persisted throughout about 370 million-year-long evolutionary history of orthocerid cephalopods.

Siphonal tube structure of the Late Devonian orthocerid Dolorthoceras from the Polar Urals (NW Russia) preserving nacre and organic fibres as well as its persistence in cephalopod evolution

Article

Full-text available

Mar 2019

Larisa Doguzhaeva

A juvenile orthocerid Dolorthoceras sp. from the Frasnian (Late Devonian) of the Polar Urals in NW Russia is the first recorded ectocochleate cephalopod showing fibrous structures and the first Devonian cephalopod preserving nacreous structures within its conch. Like Nautilus, Dolorthoceras sp. has columnar nacre in its shell wall and septa, which are composed of differentiated nacreous tablets that are c. 3 µm and 10 µm in diameter. The central, small, cylindrical, hollow siphonal tube—studied in median section using scanning electron microscope—comprises short columnar-nacreous suborthochoanitic septal necks and thin, apparently primarily chitinous, connecting rings; swollen, lens-shaped in median section, two-part fibrous non-biomineralized structures—here named clutches—envelope the posterior parts of the septal necks. Together with the adjacent connecting ring, the outer part of the clutch may extend onto adapical septal surfaces; their inner part and adjoining from inside next connecting ring line the septal neck. The clutches are comparable, to some degree, to the auxiliary deposits and cuffs of the siphonal tubes found in ammonoids; these are interpreted as being protective structures of the conjunctions between the connecting rings and septal necks reinforcing it against hydrostatic pressure, which was probably also the case in Dolorthoceras. Tracing the Silurian to Cretaceous longiconic cephalopods with narrow, central to eccentric, hollow siphonal tubes and swollen posterior portions of the septal necks shows that the Dolorthoceras-type siphonal tube may represent a conch structure that persisted throughout about 370 million-year-long evolutionary history of orthocerid cephalopods.

Overcoming the constraints of spiral growth: the case of shell remodelling

Article

Aug 2020

Geerat Vermeij

As animals grow in size, their relationship to the physical environment necessarily changes, but molluscs and brachiopods whose accretionary skeletons expand at one end of a hollow cone conform to logarithmic‐spiral growth and retain a constant shape. Dissolution and remodelling of previously formed parts of the skeleton can alleviate the constraints of strict logarithmic‐spiral growth. How, when, where and in which clades mineral skeletal resorption has evolved are important questions because they relate to the conditions and history of skeletal formation and to the way in which ocean acidification in the past influenced that history. A synthesis of data on mineral dissolution in shells shows that resorption from the inner surface of bivalve shells occurs under temporarily anaerobic conditions within the closed shell, but functional remodelling is unknown in bivalves. Resorption and functional remodelling occur in brachiopods, gastropods and terrestrial hermit crabs, and to a lesser extent in scaphopods and cephalopods. Internal whorl resorption leading to a more compact visceral mass has evolved at least ten times in gastropods. Contrary to expectations stemming from patterns in the availability of calcium, gastropod remodelling is a phenomenon of warm, calcium‐rich environments and not of cold acidified conditions. There is therefore no evidence that internal whorl resorption increases calcium‐use efficiency. Resorption is one of several mechanisms that have enabled animal skeletons to become more dynamic and adaptable during ontogeny.

An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda

Article

Full-text available

Aug 2019

Martin Ross Smith

Nectocaridids are soft-bodied Cambrian organisms that have been controversially interpreted as primitive cephalopods, at odds with the long-held belief that these mollusks evolved from a shell-bearing ancestor. Here, I document a new nectocaridid from the Whetstone Gulf Formation, extending the group's range into the Late Ordovician. Nectocotis rusmithi n. gen. n. sp. possesses a robust internal element that resembles a non-mineralized phragmocone or gladius. Nectocaridids can be accommodated in the cephalopod total group if the earliest cephalopods (1) inherited a non-mineralized shell field from the ancestral mollusk; and (2) internalized this shell field. This evolutionary scenario would overturn the traditional ectocochleate, Nautilus -like reconstruction of the ancestral cephalopod, and indicate a trend towards increased metabolic efficiency through the course of Cambrian–Ordovician evolution. UUID: http://zoobank.org/ed594200-37b9-4642-bd8f-4fb72dc544eb

Astrovioidea: A new superorder of Paleozoic cephalopods

Article

Full-text available

Jan 2004

A new superorder of Paleozoic ectochochlian cephalopods, Astrovioidea superordo nov., is designated. A distinctive feature of this superorder is that the soft cameral tissue enters the siphon cavity and secrets calcareous cameral deposits. This resulted in the destruction of the connecting rings that previously constituted, in conjunction with the septal necks, the compound wall of the siphon. In early (Ordovician) representatives of this superorder, the soft cameral tissue passed through the siphon to destroy, either partially or completely, the connecting rings and to progress occasionally along the internal surface of those rings that remained undestroyed as far as several chambers (the order Lituitida Starobogatov, 1983). In later (Silurian and Devonian) astrovioids, the cameral tissue entered the siphon cavity through the septal foramen. The episeptal portion of the cameral tissue destroyed the connecting ring and moved over the septal neck to the earlier chamber to be fused with the hyposeptal portion of the cameral tissue located in this chamber. Subsequently, it gradually secreted calcareous deposits, thus squeezing the soft siphon in the septal neck. As cameral deposits accumulated, they filled the cavities of chambers and often came out from them to move toward the siphon and squeeze the soft siphon not only in the septal necks, but (in the absence of connecting rings) in the interspaces between them as well (the order Pallioceratida Marek, 1998). A detailed examination of thin and polished sections of newly found and some previously published Silurian and Devonian pallioceratids by an optical microscope and, what is more important, by a scanning electron microscope has shown that, in those parts of the phragmocone within which cameral deposits reached into the siphon cavity, the connecting rings were completely destroyed, thus allowing direct connection between the soft cameral and soft siphonal tissues. In addition, some new taxonomically important details of the internal structure of shells have been revealed. Thus, it has been found that many taxa of this group of cephalopods formed in the siphon cavity a longitudinal layer of calcareous deposits that passed through all chambers over the epi- and hyposeptal deposits that filled the chambers. We propose the term metacameral deposits for these deposits. Furthermore, some pallioceratids contain calcareous deposits that in the absence of connecting rings were secreted by the siphon directly in the chamber cavity to meet the cameral deposits. These deposits will be referred to as ectosiphonal deposits. The microstructure of the cameral, metacameral, and ectosiphonal deposits have been examined with the aid of SEM. These new data on the internal structure of pallioceratid shells and a detailed analysis of the literature that has been made in the light of these data allow the extension of the composition of this order and the development of a new classification. Thus, the order Pallioceratida now includes 5 families, 15 genera, and 32 species. The following new taxa have been separated: the families Flowerinidae, Ostreioceratidae, Astroviidae, and Plicatoceratidae; the genera Astrovia (with the type species A. adorea sp. nov.), Ostreioceras (with the type species Sinoceras riphaeum Zhuravleva, 1978), and Syndikoceras (with the type species S. arcticum sp. nov.); and the species Astrovia marhoumensis sp. nov., Syndikoceras mutveii sp. nov., and Plicatoceras bublichenkoi sp. nov. At present pallioceratids are known from the Wenlock through the Eifelian of Europe, Asia, Africa, and North America. The fact that in the order Lituitida cameral deposits penetrated into the siphon cavity and resulted in a destruction of connecting rings during the life of the organism was convincingly shown by Sweet (1958), Flower (1978), Dzik (1984), and other authors. The superorder Astrovioidea existed from the Early Ordovician to approximately the Middle Devonian (Eifelian) and was virtually worldwide.

On the relations of the principal muscles to the shell in Nautilus and some fossil nautiloids

Article

Jan 1957

Harry Mutvei

Nautiloid systematics based on siphuncular structure and position of muscle scars

Article

Jan 2002

Harry Mutvei

The protoconch of a specimen of the genus Orthoceras of the Early Paleozoic

Article

Jan 1957
Dokl Akad Nauk SSSR

Z.G. Balashov

Fossil erhaltungsfähige Merkmalskomplexe der Coleoidea (Cephalopoda) und ihre phylogenetische Bedeutung

Article

Jan 2006

Dirk Fuchs

Gradual opening of the siphonal tube in an orthoconic cephalopod from the Silurian of Central Bohemia (Czech Republic)

Article

Jan 1999

I. Kolebaba

A specimen of an orthoconic cephalopod from the Silurian (Ludlow, Ludfordian), Kopanina Formation of Central Bohemia, described by Barrande (1870) as Orthoceras obelus, has been studied in detail. New information was obtained on the morphology of the sipho-cameral structures; the gradual opening of the siphonal tube, enabling the tissue to enter the gas chambers during the ontogeny, has been found out. The specimen was established the holotype of a new species Nucleoceras hollandi sp. n., and was, based on the proved presence of the cameral mantle, attributed to the Family Lamellorthoceratidae Teichert, 1961, Order Pallioceratida Marek, 1998.

Pallioceratida ordo n. - a new order of the Palaeozoic cephalopods (Mollusca, Cephalopoda)

Article

Jan 1998

J. Marek

Based on the original presence of a soft tissue in the gas chambers of the Palaeozoic nautiloid cephalopods, a new order Pallioceratida ordo n. is established. Two distinct groups - families Lamellorthoceratidae Teichert, 1961 and Leurocycloceratidae Sweet, 1964 belong to this order.

The nautiloid order Ellesmeroceratida (Cephalopoda)

Article

Jan 1964

R.H. Flower

A contribution to the theory of the cameral mantle in some Silurian Nautiloidea (Mollusca, Cephalopoda)

Article

Jan 2002

I. Kolebaba

Plagiostomoceras vestigium sp. n., a new species of orthoconic cephalopods from the Silurian (Ludlow, Ludfordian, Kopanina Formation) of Central Bohemia, is described. Based on the proved original presence of the cameral mantle in gas chambers, the described species has been assigned to the family Leurocycloceratidae, order Pallioceratida Marek, 1998. Three morphological types of the cameral mantle have been distinguished in six species of Protobactrites, Plagiostomoceras, Nucleoceras and Murchisoniceras, in which this tissue has been proved. Characteristic cross-sections of their gas chambers are figured.

Living Nautilus

Article

Jan 1964

H.B. Stenzel

"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

Abstract and Figures

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