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Chapter 4
Cameral Membranes, Pseudosutures, and Other
Soft Tissue Imprints in Ammonoid Shells
Kristin Polizzotto, Neil H. Landman and Christian Klug
© Springer Science+Business Media Dordrecht 2015
C. Klug et al. (eds.), Ammonoid Paleobiology: From Anatomy to Ecology,
Topics in Geobiology 43, DOI 10.1007/978-94-017-9630-9_4
K. Polizzotto ()
Department of Biological Sciences, Kingsborough Community College,
2001 Oriental Boulevard, Brooklyn, NY 11235, USA
e-mail: Kristin.Polizzotto@kingsborough.edu
N. H. Landman
Division of Paleontology (Invertebrates), American Museum of Natural History,
Central Park West at 79th Street, New York, NY 10024, USA
e-mail: landman@amnh.org
C. Klug
Paläontologisches Institut und Museum, University of Zurich,
Karl Schmid-Strasse 6, 8006 Zurich, Switzerland
e-mail: chklug@pim.uzh.ch
4.1 Introduction
An essential aim of ammonoid paleobiology is understanding the growth, locomo-
tion, and mode of life of these animals. Evidence of these processes can be gathered
from the remains of soft tissues or their traces preserved inside the shell such as
cameral membranes, pseudosutures, and muscle scars, as well as other soft tissue
imprints. Although these structures have been recognized for at least 100 years, in
the last 15 years many important studies relating to their occurrence, ultrastructure,
composition, and probable function have been published. This chapter summarizes
previous research and focuses on recent advances in understanding cameral mem-
branes, pseudosutures, drag lines, and soft tissue imprints unrelated to muscle at-
tachment.
K. Polizzotto et al.
92
4.2 Cameral Membranes
Cameral membranes (or cameral sheets) are the remains of thin, originally organic
structures within the chambers of ammonoids (Fig. 4.1). The term “cameral sheets”
is preferred by some in order to avoid the implication of a physiological, cellu-
lar membrane, but either term is widely accepted. These structures can be divided
into two general types: chamber linings, which coat the internal surfaces of the
chambers, and suspended sheets, which are three-dimensional sheets internally at-
tached to the shell at two or more different points (Landman et al. 2006, Polizzotto
et al. 2007) or along longer lines. Suspended sheets may occur as siphuncular mem-
branes, which extend between the siphuncle and the septum and/or ventral shell
floor; transverse membranes, which extend between different points on the septum;
and horizontal sheets, which divide the chamber into dorsal and ventral compart-
ments (Weitschat and Bandel 1991).
4.2.1 Taxonomic Occurrence
Cameral membranes have been described in the ammonoid literature for over a cen-
tury (John 1909; Grandjean 1910; Schoulga-Nesterenko 1926; Hölder 1952, 1954;
Schindewolf 1968; Erben and Reid 1971; Westermann 1971; Bayer 1975; 1977;
Bandel and Boletsky 1979; Kulicki 1979; Bandel 1981, 1982; Tanabe et al. 1982;
Hagdorn 1983; Grégoire 1984; Henderson 1984; Weitschat 1986; Weitschat and
Bandel 1991; Keupp 1992; Checa and Garcia-Ruiz 1996; Kulicki 1996; Tanabe and
Landman 1996). The taxonomic occurrence of the membranes reported in these pub-
lications is wide, including phylloceratids, lytoceratids, ceratitids and ammonitids.
More recently, such membranes have also been found in Paleozoic ammonoids such
as goniatites (Polizzotto et al. 2007) and prolecanitids (Mapes et al. 2002, Landman
et al. 2006) as well as in Cretaceous scaphitids (Polizzotto and Landman 2010).
Schoulga-Nesterenko (1926) reported cameral membranes in the goniatite Agath-
iceras uralicum but may have misidentified the specimen (see Polizzotto et al. 2007).
Early work most often described cameral sheets associated with the siphuncle.
Weitschat and Bandel (1991) described the most intricate and extensive cameral
membranes reported up to that time (Fig. 4.1), including transverse and horizontal
Ladinian. Berlichingen (Germany), note the membranes on both sides of the siphuncle. b C. cf.
sublaevigatus, Künzelsau, Garnberg (Germany), 0–7 m above Cycloidesbank gamma, Ladinian,
membranes on both sides of the siphuncle. c C. cf. sublaevigatus, Nitzenhausen (Germany), 70 cm
below Tonsteinhorizont 4 (delta), Ladinian, membranes on both sides of the siphuncle. d C. cf.
sublaevigatus. Nitzenhausen (Germany), between Tonsteinhorizont 3 and 4 (γ and δ), Ladinian,
phosphatized membranes on both sides of the siphuncle. e C. cf. evolutus subspinosus, Heming
(France), evolutus Zone, Ladinian, phosphatized siphuncle. f Bukkenites sp., 104, Dienerian, Amb,
Spiti valley, India, membranes on both sides of the siphuncle. g Gen. et sp. indet., 104, Amb,
Spiti valley, India. h Ambites sp., Nam 53–20, Dienerian, Nammal (Pakistan), membranes cross-
ing the saddles (separating fillings that differ in color). i, j horizontal lamellae in Aristoptychites
kolymensis, Late Ladinian, Barentsøya Formation, Bertylryggen, Spitsbergen. i detail. j note the
protoconch and the absence of horizontal sheets in the first whorls
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 93
Fig. 4.1 Siphuncular sheets and cameral membranes/intracameral lamellae in various Triassic
ammonites; images a–e courtesy of H. Hagdorn (Ingelfingen), g–i courtesy of D. Ware (Zürich), j
and k courtesy of W. Weitschat (Hamburg). a Ceratites cf. münsteri, postspinosus to enodis-Zone,
K. Polizzotto et al.
94
membranes in addition to siphuncular membranes. Since that time, transverse and
siphuncular membranes have been described in several other ammonoids as men-
tioned above, but to our knowledge, no other instances of horizontal membranes
have been reported. Brief summaries of the earlier descriptions of cameral mem-
branes can be found in Kulicki (1996) as well as Checa and Garcia-Ruiz (1996), and
detailed descriptions and images of more recent discoveries (Fig. 4.2) have been
produced by Tanabe et al. (2005), Landman et al. (2006), Polizzotto et al. (2007),
and Polizzotto and Landman (2010). These studies clarified aspects of the structure,
composition, origin, and probable function of the cameral membranes, as discussed
below.
4.2.2 Structure and Composition
The ultrastructure of the membranes has been described as thin (< 0.2 μm) con-
chiolin fibers with no consistent orientation (Tanabe et al. 1982; Grégoire 1987).
The chamber linings in particular have been compared to the pellicle in Nautilus
and Spirula, but Kulicki (1996) pointed out that the fibers of ammonoid cameral
Fig. 4.2 a Hollow chambers from a Late Cretaceous Rhaeboceras halli from Montana, USA
(modified from Polizzotto and Landman 2010). b A closer view of the siphuncular sheets and
pseudosutures from the specimen shown in a. c Siphuncular sheets in a Permian Akmilleria elec-
traensis from Nevada, USA
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 95
membranes are considerably finer. Polizzotto and Landman (2010) described a
well-preserved Late Cretaceous scaphite ( Rhaeboceras halli) in which siphuncular
membranes and chamber linings (as well as pseudosutures) were present in the
same chamber. Membranes and chamber linings are 1–2 μm thick and composed
of irregular globular particles. This is in contrast to the composition reported by
Kulicki (1996), but may be more similar to the organic layer secreted on the inner
chamber surface in Nautilus (Mutvei 1963). Study of the membranes in prolecanit-
ids confirms phosphatic composition (Tanabe et al. 2000). Energy dispersive spec-
troscopy (EDS) on the Rhaeboceras specimen indicated high phosphorus content in
the membranes and chamber linings, suggesting an organic origin (Polizzotto and
Landman 2010). This hypothesis is accepted by most researchers; however, there is
a difference of opinion as to the mode of formation of such membranes (see also the
discussion on intracameral deposits in Seuss et al. 2012).
4.2.3 Formation
Two models have been proposed for the formation of cameral membranes. The first
proposes that cameral membranes were secreted by the rear mantle as the animal
moved forward during chamber formation, and that the shape of the membranes
replicates the shape of the rear mantle (the secretion model; Weitschat and Bandel
1991). The second model contends that the membranes are simply the desiccated
remains of a hydrogel formed by cameral fluid enriched with organic molecules and
shaped by surface tension (the desiccation model; Hewitt et al. 1991; Westermann
1992; Checa 1996). Landman et al. (2006) argued that siphuncular membranes
(Fig. 4.2 and 4.4) are not solely the result of cameral liquid dehydration, based on
the absence of membranes from early whorls and a consistent first appearance at the
end of the neanic stage of ontogeny, as well as the presence of membranes in body
chambers in some ammonoids (Polizzotto et al. 2007). The formation of chamber
linings is less clear, but the similarity in ultrastructure between chamber linings and
siphuncular membranes suggests a similar origin, at least in scaphitids (Polizzotto
and Landman 2010). Evidence for the morphogenesis of transverse membranes has
not been investigated, and their overall morphology does not immediately rule out
either the secretion or the desiccation hypothesis. An examination of the ultrastruc-
ture and ontogenetic pattern of occurrence of transverse membranes may shed light
on this issue.
In summary, the secretion hypothesis is well supported for the formation of sip-
huncular membranes in at least some groups of ammonoids (prolecanitids, goni-
atites, phylloceratids, and scaphitids). There is also some evidence for the secretion
hypothesis for chamber linings in scaphitids. Cameral membranes in other ammo-
noid groups, as well as transverse membranes in all ammonoids, may have been
formed either by secretion, desiccation, or a combination of both processes (Checa
and Garcia-Ruiz 1996).
K. Polizzotto et al.
96
4.2.4 Function
Researchers have long proposed that cameral membranes functioned in absorbing
cameral fluid, either for fluid transport or for maintenance of a fluid reservoir (Mut-
vei 1967; Kulicki 1979; Kulicki and Mutvei 1988; Ward 1987; Weitschat and Ban-
del 1991; Kulicki 1996; Kröger 2002; Landman et al. 2006). This process may have
helped in decoupling fluid reservoirs, which may have conferred some physiologi-
cal benefit. Some researchers have tested a model demonstrating that the presence
of cameral membranes may have maintained a reservoir that aided in buoyancy con-
trol by rapid fluid re-filling following sublethal shell loss from injury (Daniel et al.
1997; Kröger 2002). Kröger (2002) found that ammonoids survived shell loss up to
four times greater than in Nautilus, suggesting some sort of buoyancy compensation
mechanism. The evidence from Kröger (2002) clearly indicates that a high volume
of cameral membranes (up to 14 % of the chamber volume; Hewitt and Westermann
1996) would have made a significant difference in rapidly compensating for shell
loss due to injury. Whether or not most ammonoids possessed such a volume of
cameral membranes is not yet known.
The capillary action of cameral membranes may also have aided in fluid trans-
port, resulting in faster chamber emptying and thus faster growth rates in ammo-
noids that formed such membranes. Kröger (2002) suggests that this may be one
explanation for increasingly more complex septa during the course of ammonoid
evolution, which would have added to the volume of liquid reserved in correspond-
ingly more complex and extensive cameral membranes.
Here, we suggest an additional possible function: the cameral membranes sub-
divided the chamber volume into smaller volumes. Taking the potentially large
amount of chamber water (up to 30 % of phragmocone volume; Heptonstall 1970;
Mutvei and Reyment 1973; Reyment 1973; Ward 1979; 1987; Tajika et al. 2014) in
the phragmocone into account, water movement might have altered the orientation
of the shell syn vivo. Cameral membranes would have limited the water move-
ment within the phragmocone chambers and thus enhanced stability. However, the
possible effect of moving chamber water needs to be modeled in order to test the
potential physical effect of chamber water movements.
4.3 Pseudosutures and Drag Lines
Pseudosutures are incomplete replicas of the suture that are often preserved as
raised ridges on the internal surface of the chamber or as lines or etched furrows on
the surface of the steinkern between the sutures themselves (Fig. 4.3). Pseudosu-
tures should not be confused with phantom sutures (Seilacher 1968, 1988), which
formed when the ammonoid’s surface was corroded by a pressurized solution and
a phantom of the suture was copied on a lower level of the internal mould. Pseudo-
sutures often occur in series and have sometimes been interpreted as the margins of
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 97
Fig. 4.3 Pseudosutures in various Jurassic and Cretaceous ammonites: a Cadoceras sp., Callovium,
Kostroma Region, Russia, whorl height 12 mm, image courtesy of R. Hoffmann (Bochum). b
Baculites mariasensis with multiple pseudosutures and drag lines associated with all four sutures
in the image. Pseudosutures are found near the adapical side of the lobules of each suture. Adoral
direction is to the right. c–f, Craspedites sp., Craspedites nodiger Zone, Cretaceous, Kostroma
Region, Russia, images courtesy of R. Hoffmann (Bochum). c dm 24 mm. d, dm 34 mm. e, f image
width at top 25 mm
K. Polizzotto et al.
98
pseudosepta (Hewitt et al. 1991). The replicated portion may be lobes, saddles, or
both, although pseudosutures mimicking lobes appear to be slightly more common.
The pseudosutures may be evenly spaced throughout the chamber between sutures
(Zaborski 1986), or they may occur singly or in a cluster on one side approaching
the lobe or saddle. Pseudosutures most frequently appear on the flanks or ventrolat-
eral portion of the chamber.
Drag lines (or drag bands), which are often associated with pseudosutures, are
spiral markings that often (but not always) extend throughout the chamber from
lobule to lobule. Like pseudosutures, drag lines form ridges on the internal chamber
surface, or their imprints occur as grooves in the surface of the steinkern. In well-
preserved specimens, the drag lines extend in pairs from the flanks of the lobe or
lobules (Zaborski 1986; Hewitt et al. 1991; Polizzotto and Landman 2010).
4.3.1 Taxonomic Occurrence
Pseudosutures have been described and discussed in numerous ammonoid groups
(John 1909; Hölder 1954; Vogel 1959; Schindewolf 1968; Bayer 1977; Hagadorn
and Mundlos 1983; Zaborski 1986; Seilacher 1988; Hewitt et al. 1991; Weitschat
and Bandel 1991, 1992; Westermann 1992; Landman et al. 1993; Lominadze et al.
1993; Bucher et al. 1996; Checa 1996; Checa and Garcis-Ruiz 1996; Doguzhaeva
and Mutvei 1996; Tanabe et al. 1998; Keupp 2000; Richter 2002; Richter and Fisch-
er 2002; Klug et al. 2007; Polizzotto et al. 2007; Klug et al. 2008; Polizzotto 2010;
Polizzotto and Landman 2010). The groups in which pseudosutures have been most
widely reported include ceratitids, lytoceratids, phylloceratids, perisphinctids, vas-
coceratids, scaphitids, and goniatitids, but they are found fairly often and probably
Fig. 4.4 Reconstruction of
the siphuncular sheets and the
vertical sheet in the Triassic
ammonoid Anagymnotoceras
from Spitsbergen, modified
after Weitschat and Bandel
(1991)
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 99
occur to one degree or another in most ammonoid groups. Pseudosutures have also
been noted in baculitids (Fig. 4.3b and 4.5, W.A. Cobban unpublished observa-
tions, Polizzotto 2010). Drag lines are often reported together with pseudosutures
(Fig. 4.1b, c, 4.2, Zaborski 1986; Lominadze et al. 1993; Richter 2002; Klug et al.
2007, 2008; Polizzotto and Landman 2010).
4.3.2 Structure and Composition
Pseudosutures form ridges on the internal surface of the shell, but the imprints (fur-
rows or grooves) of these ridges on the surface of the steinkern are also called
pseudosutures. The height and width of the ridges vary, with some pseudosutures
quite prominent (20 μm wide and 25 μm high; see Polizzotto et al. 2007), and others
less so (2 μm wide and 10 μm high; see Polizzotto and Landman 2010). Drag lines,
while oriented differently than pseudosutures (parallel to the direction of growth
rather than parallel to sutures; Richter 2002), appear to have a similar morphology
in width and height (Polizzotto and Landman 2010).
Fig. 4.5 Eubaculites latecarinatus from the Late Cretaceous Owl Creek Formation, Mississippi,
USA. The upper left image (a) is the mould, and the upper right image (b) is the corresponding
shell fragment. Each image shows the suture line, as well as associated pseudosutures. The lower
left image (c) is a closer view of some of the suture and pseudosutures on the mould. EDS analysis
indicates phosphorus enrichment in the pseudosutures and chamber surface (d), but no phosphorus
is present on the inner surface of the shell (see text for explanation)
K. Polizzotto et al.
100
The original composition of pseudosutures and drag lines is still unclear. Po-
lizzotto et al. (2007) figured various goniatitid pseudosutures in the same speci-
men, some of which were made up of regular crystals arranged vertically along
an asymmetrical slope (similar to the mural ridge in Nautilus), and others with a
more random crystal arrangement. The pseudosutures in these goniatites sometimes
dissolved when etched in acid, indicating an underlying carbonatic composition.
At other times, however, the pseudosutures remained intact following etching, and
were assumed in such cases to be coated by a now phosphatic and probably origi-
nally organic layer. In support of this idea, the thinner pseudosutures described by
Polizzotto and Landman (2010) in a scaphitid were composed of (or perhaps coated
with) an irregular, globular substance 1–2 μm thick. EDS analysis of these pseu-
dosutures and of the drag lines in the same chamber revealed a high phosphorus
content, corroborating an originally organic composition (at least for the surface of
the pseudosutures and drag lines). Recent EDS analysis of well-preserved baculi-
tids also indicated phosphorus enrichment (8–10 weight %) in pseudosutures (Po-
lizzotto 2014). In that study, the shell was carefully removed from the mould, and
pseudosutures on the surface of the mould were analyzed (Fig. 4.5). In addition, the
imprints of pseudosutures on the inner surface of the corresponding shell fragment
were analyzed. It is interesting to note that although phosphorus enrichment was
found in the pseudosutures themselves, it was absent in the imprints. This implies
that pseudosutures may have been composed of an originally mineralized substance
(similar to the shell and septum), and then coated with an organic secretion that
likewise coated the entire interior of the chamber (see also Polizzotto et al. 2007
and Polizzotto and Landman 2010). When the shell was removed from the mould,
the originally organic coating adhered to the mould, explaining the presence of
phosphorus on the mould and its absence on the inner shell surface. Though more
evidence is needed in additional taxa, it seems likely that the original composition
of pseudosutures and drag lines was carbonatic, with an overlying organic coating.
It should be possible to verify this by performing EDS analysis on cross-sections
of well-preserved pseudosutures. This hypothesis for the composition of pseudostu-
rues leads to the question of how these structures were formed.
4.3.3 Formation
Pseudosutures likely formed as an accumulation of secretions from the rear man-
tle during pauses in forward movement (Weischat and Bandel 1991; Keupp 2000;
Landman et al. 2006; Klug et al. 2007; Polizzotto et al. 2007 and references therein).
It has also been proposed that siphuncular membranes and pseudosutures formed
by a single process as parts of a continuous structure, and that both siphuncular
membranes and pseudosutures are simply the remnants of pseudosepta (originally
organic membranes that replicated the entire surface of the rear mantle; Hewitt
et al. 1991; Westermann 1992; Checa 1996). These pseudosepta would have formed
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 101
by either secretion or desiccation, as outlined earlier. We have described evidence
above in favor of the secretion hypothesis for siphuncular membranes, and similar
evidence suggests that pseudosutures formed by secretion as well (Polizzotto et al.
2007; Polizzotto and Landman 2010).
In addition, recent research has demonstrated that although siphuncular mem-
branes and pseudosutures formed by a similar process (as accumulations of secreted
material in the shape of the rear mantle), they are not parts of a single continuous
structure (Polizzotto et al. 2007; Polizzotto and Landman 2010). This was con-
firmed by examining specimens in which siphuncular membranes and pseudosu-
tures occurred in the same specimen or even in the same chamber, which revealed
that differences in ultrastructure, position in the chamber, and spacing argue against
the single-origin hypothesis.
If it is the case that pseudosutures are composed of an originally mineralized
ridge overlain by an originally organic secretion, then two hypotheses of forma-
tion are possible. Either two separate but closely located populations of rear mantle
cells produced two different secretions in sequence, or the same population of cells
produced two different secretions at various points in the chamber formation cycle.
It is difficult to test either hypothesis, but it may be fruitful to identify the specific
cells that secrete organic and inorganic components of modern molluscan shells.
Drag lines have always been assumed to mark the progress of the rear mantle
during translocation, and similarities to pseudosutures in structure and composi-
tion suggest that drag lines represent an accumulation of rear-mantle secretions. In
contrast to the portion of the rear mantle that secreted pseudosutures, however, the
parts of the mantle that formed drag lines must have remained in continuous contact
with the shell wall. Alternatively, Klug et al. (2008) hypothesized that some spirally
arranged drag lines might represent impressions of muscle fiber bundles in the pos-
terior mantle (rather than secretions).
4.3.4 Implications for Growth
The shape of the pseudosutures and their probable origin as secretory products of
the rear mantle corroborates the hypothesis that they formed during pauses in the
forward movement of the animal. Many authors have proposed such an explanation
for pseudosutures (e.g., Zaborski 1986; Seilacher 1988; Hewitt et al. 1991; Lomi-
nadze et al. 1993; Checa and Garcia-Ruiz 1996; Polizzotto et al. 2007; Polizzotto
and Landman 2010). Interpretations differ, however, in what the pseudosutures re-
veal about the process of translocation. Some suggest that the temporary points of
attachment served as critical, possibly genetically determined points that helped to
maintain the shape of the rear mantle (and thus the consistent shape of the septum)
between septa (Henderson et al. 2002; Polizzotto and Landman 2010). This line
of reasoning gives rise to the hypothesis that the pseudosutures represent points of
temporary attachment for the rear body during translocation (Klug and Hoffmann
2015). In any animal possessing a chambered shell, growth requires repeated de-
K. Polizzotto et al.
102
tachment of the body from the shell, yet it is unlikely that the animal would have
detached the entire body simultaneously. It is clear that Nautilus attaches to the
mural ridge prior to septal formation, and it appears likely that extinct nautiloids,
bactritoids, early coleoids, and many ammonoids did the same. Given the extremely
similar morphology and ultrastructure of at least some ammonoid pseudosutures to
the mural ridge (Polizzotto et al. 2007), it is possible that pseudosutures also repre-
sent points of temporary attachment, at least in some instances. As the occurrence of
pseudosutures at particular points along the suture is remarkably consistent within
species, this corresponds well to the tie-point hypothesis of septal morphogenesis,
first proposed by Seilacher (1975, 1988).
Some have interpreted drag lines as candidates for these tie points (Zaborski
1986; Seilacher 1988); others, however, point out that the coincidence of drag lines
with the flanks of the lobules rather than the tips, and their paired occurrence, sug-
gests that drag lines are more likely fused, telescoped pseudosutures (Hewitt et al.
1991; Checa and Garcia-Ruiz 1996; Klug et al. 2007; Klug and Hoffmann 2015).
Polizzotto and Landman (2010) reported several different drag lines in a single
chamber, none of which were continuous with the pseudosutures in the same cham-
ber. Additionally, some of the drag lines in this specimen were paired and appar-
ently diverged from a single drag line adapically (Polizzotto and Landman 2010,
Fig. 5, 6), while other, single drag lines continued nearly all the way to the lobule
before ramifying into a short series of concentric ridges at the base of the lobule
(Polizzotto and Landman 2010, Fig. 7). Based on observations from all these differ-
ent specimens, it may be that drag lines formed in more than one way, but in every
case they represent a point at which the rear mantle was in contact with (and pos-
sibly attached to) the inner shell wall.
An alternative interpretation of pseudosutures proposes that rather than acting
as points of attachment, they may represent accumulations of secreted material at
points determined by the interaction of the viscoelastic rear body and the varying
pressure of cameral fluid and gas behind the body (Checa and Garcia-Ruiz 1996).
The mantle did not necessarily attach at the location of the pseudosutures, but sim-
ply paused. This corresponds to the viscous fingering model of septal morphogen-
esis (Garcia-Ruiz et al. 1990; Garcia-Ruiz and Checa 1993; Checa and Garcia-Ruiz
1996). This model, however, would not explain the evidence of the attachment-like
ultrastructure in at least some pseudosutures.
Klug et al. (2008) introduced a “tension model” of septal morphogenesis that
incorporates elements of both the tie-point model and the viscous fingering model,
in which muscle fibers at the edge of the rear mantle attached to the inner shell, and
the more complex the shape of the septum, the more tension could develop in the
rear mantle and in the organic pre-septum prior to mineralization. While Klug et al.
(2008) did not elaborate specifically on the consequences of this model for the for-
mation of pseudosutures, the model implies that the shape of temporary attachment
points would have depended on components of translocation that were not so much
genetically influenced, but mainly affected by changes in chamber pressurization.
For more details on septum formation see Klug and Hoffmann (2015).
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 103
In addition to implications for septal morphogenesis, the number, placement, and
spacing of pseudosutures may indicate the pace and timing of chamber formation.
These interpretations, however, rely on the assumption that pseudosutures were se-
creted periodically, which is currently not possible to verify. These pauses, if they
are such, might also correspond to growth rhythms recorded in growth lines or lirae
formed at the aperture; however, this hypothesis has not yet been tested. There does
not seem to be any analogous structure or process in Nautilus or Sepia, leaving us
with little to substantiate the periodicity of pseudosuture formation one way or the
other. The only similar structure seen in modern nautilids are spiral drag lines, pos-
sibly representing imprints of mantle muscle fibers and/or fine arteries in the mantle
(Klug et al. 2008).
In summary, it appears plausible that pseudosutures record short pauses in
forward movement during the chamber formation cycle, and it is likely that at
least some pseudosutures (or pseudosutures in some taxa) represent the im-
prints of ephemeral soft-tissue attachment. Drag lines do not offer any evidence
of the pace of translocation or of pauses, but they do show that at least some
parts of the mantle were in continuous contact with the shell wall and may have
formed attachment points. Such attachments may have helped to anchor parts
of the animal in the body chamber during translocation, as well as helping to
maintain the fundamental shape of the rear mantle in between formation of
consecutive septa.
4.4 Other Soft Tissue Imprints
Other soft tissue imprints, particularly on the septum, have been recently described
in ammonoids by Klug et al. (2008) (Fig. 4.6). These include the septal furrow
and associated subparallel furrows (extending from the mid-dorsal suture to the
siphuncular perforation); striations on the mural band and on the annular elevation;
the conchal furrow on the venter (especially on the body chamber); and deformed
septa (non-taphonomic deformities). These specific features had previously been
reported only in nautiloids and bactritoids (Klug et al. 2008 and references therein),
and were interpreted as the imprints of muscle fibers and blood vessels in the septal
mantle. The presence of these features in nautiloids, bactritoids, and early ammo-
noids (Devonian), and their apparent absence in more derived ammonoids (with the
exception of the conchal furrow, which appears in Cretaceous ammonites, Land-
man and Waage 1993), led Klug et al. (2008) to hypothesize that higher tension in
the organic pre-septum due to the higher order septal folding may have prevented
imprinting of soft tissue structures (see the summary of Klug et al.’s tension model
of septal formation above).
Klug et al. (2007) found a black layer on the dorsal surface of some ammonoid
shells (see also Keupp 2000). This layer is presumably originally organic and most
likely similar to the black layer found in recent and fossil nautiloids.
K. Polizzotto et al.
104
Fig. 4.6 Soft-tissue imprints in the shell and septa of Early Devonian ammonoids, modified after
Klug et al. (2008). a–c, Erbenoceras advolvens (Erben 1960), PIMUZ 7494, early Emsian, Hassi
Chebbi, Tafilalt, Morocco, length 13 mm. a Septal view to show the septal furrow. b Lateral view.
4 Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in … 105
4.4.1 Blood Vessel Imprints
Some septa of the Early and Middle Devonian ammonoids Chebbites, Erbenoceras,
Gracilites, Metabactrites, Rherisites, and Pinacites show long wrinkles on the sur-
face (Klug et al. 2008). Some of these wrinkles lie in the plain of symmetry (sep-
tal furrow; Stenzel 1964; Teichert 1964; Chirat and von Boletzky 2003) and some
diverge from the plain of symmetry at a low angle, originating near the siphuncle
(Fig. 4.6). Similar shallow imprints can be seen in modern nautilids: In some Nau-
tilus conchs, Klug et al. (2008) found imprints of the left and right septal arteries,
the siphuncular artery and the accessory siphuncular arteries (see also Deecke 1913,
and Stenzel 1964, who figured a Nautilus septum showing soft tissue imprints).
Corresponding to this fact, the imprints on the septa of the Devonian ammonoids
were interpreted as imprints of arteries, providing the septal mantle with arterial
blood. The absence of these structures in more derived ammonoids has been linked
with the increase in septal frilling, which might be linked with a higher tension of
the organic septum prior to mineralization. Accordingly, the more tightly stayed
pre-septum would have prevented the formation of soft-tissue impressions in the
septum.
On the inside of the shell wall, both nautiloids and ammonoids of various ages
show the conchal furrow (“Fadenkiel” of von Bülow 1918; see also Teichert 1964;
Shimanskij 1974; Landman and Waage 1993; Chirat and von Boletzky 2003; Keupp
2012). This furrow can be traced in nautilids from the cicatrix to the aperture, while
in ammonoids, no corresponding structure has yet been found on or near the initial
chamber. In ammonoids, it is rarely seen but throughout the entire phylogeny of
ammonoids from the Early Devonian to the Late Cretaceous (Landman and Waage
1993; Klug et al. 2008). Doguzhaeva and Mutvei (1996) suggested that this mid-
ventral longitudinal elevation was the “attachment site for a ligament or a muscle
used to maintain the shape and position of the circumsiphonal invagination during
the growth and forward migration” of the soft body (Chirat and von Boletzky 2003,
p. 168). Griffin (1900, fig. 11) illustrated the “lesser aorta and its branches”, includ-
ing the midventrally running pallial artery. Potentially, it may have been this artery
that occasionally left a mid ventral imprint on the inside of the shell of various
ectocochleates.
c Ventral view. d Chebbites reisdorfi Klug (2001), PIMUZ 27000, septal view, early Emsian, Hassi
Chebbi, Tafilalt, Morocco; note the septal furrow and additional subparallel furrows on the right;
length 15 mm. e, f, Rherisites sp., PIMUZ 27072, early Emsian, Hassi Chebbi, northern Tafilalt,
Morocco; length 16 mm. e Ventral view, note the conchal furrow. f Lateral view, note the epizoans.
G, H, The ammonoid Gracilites sp., PIMUZ 27070, early Emsian, Hassi Chebbi, northern Tafilalt,
Morocco; length 30 mm. g Lateral view, note the pseudosutures. h Septal view, note the striations
that run subparallel to the plane of symmetry. i-l, Metabactrites ernsti Klug et al. (2008), PIMUZ
7404, early Emsian, Ouidane Chebbi, Tafilalt, Morocco, length 25 mm. i detail of note the septal
furrow, the striation on the mural part of the septum and the striation in the body chamber (prob-
ably within the attachment site of the dorsal muscle); height of detail 1.6 mm. j Ventral view. k
Lateral view. l Dorsal view. m Agoniatitida gen. et sp. indet., MB.C.0782, late Emsian, Wissen-
bach Slate, Wissenbach, Germany
K. Polizzotto et al.
106
4.4.1.1 Muscle Imprints
Similar to the above mentioned arteries, bundles of muscle fibers in the posterior
mantle might have left imprints on the septum as well as on the inside of the outer
shell, as noted in some Devonian ammonoids (Klug et al. 2008). This can also
be seen in nautilids (Deecke 1913; Stenzel 1964), where the orientation of some
imprints coincides with the orientation of muscle fibers in the septal mantle (Klug
et al. 2008). In agreement with the findings in modern nautilids, both the spirally
arranged drag lines on the inside of the shell and the radially arranged impressions
on the margin of the septum on its mural part (Fig. 4.6i) were interpreted as imprints
of mantle musculature (Klug et al. 2008). Of course, attachment scars of various
larger muscles are occasionally seen in well preserved ammonoid specimens. These
structures are described in Doguzhaeva and Mapes (2015).
4.4.1.2 Other Imprints
From a few ammonoid taxa, tension wrinkles have been described (Checa and Gar-
cia-Ruiz 1996; Klug et al. 2007). These wrinkles are one to several micrometers
wide and ten to several tens of micrometers long. They are situated at the mural
part of the septum. According to Checa and Garcia-Ruiz (1996), these wrinkles
document the flexibility of the organic membrane prior to the mineralization of the
septum. For an illustration, see Klug and Hoffmann (2015).
Acknowledgements The authors are grateful to Helmut Keupp (Berlin) and Anthea Lacchia
(Dublin) for helpful reviews of the manuscript. Some of the results presented herein were obtained
in the course of the research projects funded by the Swiss National Science Foundation SNF,
#200021–113956⁄1, #200020–25029, and #200020–132870. Some of the images were kindly pro-
vided by Hans Hagdorn (Ingelfingen), David Ware (Zürich), René Hoffmann (Bochum) and Wolf-
gang Weitschat (Hamburg). We greatly acknowledge these contributions.
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AQ3
