Content uploaded by Dieter Korn
Author content
All content in this area was uploaded by Dieter Korn
Content may be subject to copyright.
Cravenoceras leion Bisat 1930 has long been regarded the
index fossil for the base of the Namurian Series, i.e. the base
of the Pendleian Stage (Bisat 1930; cf. Horn 1960). Originally
described from an outcrop in Light Clough, near Wiswell in
North Lancashire (Calver & Ramsbottom 1961), it was later
reported from many localities in northern England, Ireland, as
well as continental Europe. However, many of the records
refer to fragmentary or partially preserved material, such as
crushed impressions in shales.
The revision of the goniatite faunas from the Kulmplat-
tenkalk Formation of the Rhenish Massif in Germany (Korn
1988) led to the conclusion that putative specimens of
Cravenoceras leion from the basal Namurian portion of this
rock unit should be reassigned to either Emstites schaelken-
sis (Brüning 1923) or Emstites novalis (Korn 1988) and that
there is no evidence for Cravenoceras leion in the Rhenish
Massif. Unfortunately, at that time the ontogenetic develop-
ment of Cravenoceras leion was poorly known, hampering
clear separation of the very similar early cravenoceratids.
With the excellently preserved material of Cravenoceras leion
from Backdale Mine, described below, the ontogeny of conch
geometry, as well as suture line, can now be described in
detail, and differences between the species established
precisely.
1. MATERIAL
The material described here was collected by J. W. T. from
an opencast quarry at the mine adit cutting, Backdale Mine,
Hassop Derbyshire [SK 2319 7343] (Fig. 1), which provides
good exposure across the Visean–Namurian Boundary. The
C. leion Marine Band, a 30–35 cm thick limestone unit (Fig.
2), can also be found in the adjacent workings. Aitkenhead
et al. (1985) stated that, at the mine, the basal Namurian
with C. cf. leion overlies (probably unconformably) beds
referred to as Eyam Limestones. British Geological Survey
Sheet SK 27 SW also records C. leion at nearby exposures
[SK 2352 7356]. These outcrops occur on the southern limb of
the Longstone Edge Anticline, a broad asymmetrical
Variscan fold with dips ranging up to 45° . The local stratig-
raphy is complex due to a Late Brigantian disconformity, ero-
sional events and possible lateral passage between the Eyam
Limestones and Longstone Mudstones (Aitkenhead et al.
1985).
The C. leion Marine Band at Backdale Mine has yielded
solid Cravenoceras, Edmooroceras and Girtyoceras. They are
associated with brachiopods (chonetoids, productoids, spirif-
eroids), nautiloids (orthoconic and stroboceratid), ostracods
with rarer crinoids, fish debris and trilobites (Paladin and a
new genus). The apparent absence of bivalves and gastropods
is unusual. Each faunal group has a characteristic distribution
pattern within the marine band. For a recent description of
Namurian marine faunal phases and depositional environ-
ments see Brandon et al. (1995).
A total of 39 goniatite specimens are available for study.
The goniatites are preserved as calcite shells with their conchs
filled with limestone, the matrix lithology of the marine band.
Most are exfoliated and thus lack fine surface detail and
ornament. Suture patterns are visible on the inner whorls.
2. SYSTEMATIC PALAEONTOLOGY
Descriptive terms of the conch features are adopted from
Korn (1988). The main conch dimensions measured (Fig. 3;
Tables 1, 2) are conch diameter (dm), whorl width (ww),
whorl height (wh), umbilical width (uw) and apertural height
(ah). A very important conch parameter is the whorl expan-
sion rate (WER). It can be calculated by the algorithm used
by Korn (2000): WER = [dm/(dmah)]2. The imprint zone
rate (IZR) is a ratio that characterizes the whorl overlap. It
can be calculated using the following equation: IZR =
(whah)/wh.
© Yorkshire Geological Society, 2002
PROCEEDINGS OF THE YORKSHIRE GEOLOGICAL SOCIETY, VOL. 54, PART 2, PP. 111–119, 2002
A well-preserved early Namurian ammonoid fauna with
Cravenoceras leion Bisat 1930 from Backdale Mine,
Hassop, Derbyshire, England
D. KORN1and J.W.TILSLEY2
1Museum für Naturkunde, Humbold-Universität zn Berlin,Invalidenstraße 43,10115 Berlin, Germany (e-mail:dieter.korn@museum.hu-berlin.de)
22 Ansell Road,Sheffield S11 7PE, UK
SUMMARY: The Cravenoceras leion Marine Band at Backdale Mine has yielded a stratigraphically important ammonoid fauna
consisting of the species Cravenoceras leion Bisat 1930, Edmooroceras medusa (Yates 1961) and Girtyoceras sp. C. leion, in particu-
lar, is represented by well preserved material, allowing the description of the entire ontogeny. It is demonstrated that the conch
geometry of this species undergoes major transformations, and that the suture line is characteristic of the genus Cravenoceras.
Based on the ontogenetic development of the suture line, a clear separation can be made from the Rhenish species Emstites
schaelkensis (Brüning 1923).
Family CRAVENOCERATIDAE Ruzhencev, 1957
Genus CRAVENOCERAS Bisat, 1928
Cravenoceras leion Bisat 1930 (Figs 4A–D, 5, 6, 7A–C)
1930 Cravenoceras leion Bisat, p. 28.
? 1947 Cravenoceras leion Bisat; Gill, p. 62.
? 1950 Cravenoceras leion Bisat; Bisat, p. 21, fig. la–f.
1953 Cravenoceras leion Bisat; Stephens et al., p. 91, pl. 6
fig. 2.
non 1960 Cravenoceras leion Bisat; Horn, p. 333, pl. 1 fig. 8.
[= Emstites schaelkensis (Brüning 1923)]
1961 Cravenoceras leion Bisat; Calver & Ramsbottom,
p. 207, pl. 11 figs 5, 6.
? 1962 Cravenoceras leion Bisat; Johnson et al., pl. 22 figs
9–14.
non 1968 Cravenoceras leion Bisat; Figge, p. 270, pl. 47 fig. 4.
[= Emstites schaelkensis (Brüning 1923)]
1984 Cravenoceras leion Bisat; Palframan: 217, fig. 4B,C,
pl. 1 fig. 7.
1988 Emstites leion (Bisat); Korn, p. 141, fig. 74c.
Holotype. Specimen LI 1639a, Manchester Museum.
Typelocalityand horizon. Light Clough, Wiswell, Lancashire;
Bowland Shales, basal Namurian (Pendleian Stage strato-
type).
Diagnosis.Cravenoceras with pachyconic conch (ww/dm =
0.80) at 10–15 mm conch diameter, umbilicus moderately
narrow (uw/dm = 0.25). At 25–35 mm diameter, conch pachy-
conic (ww/dm =0.70) with moderately narrow umbilicus
(uw/dm = 0.20–0.25). Ornament with fine, uncrenulated
growth lines that run with a convex arc over the flanks and
form a shallow, wide ventral sinus. Few spiral lines on the
umbilical edge. Internal cast with deep constrictions. Suture
112 D. KORN & J. W. TILSLEY
LONDON
Derbyshire
Glossop
Buxton
Derby
Chesterfield
Matlock
Castleton
Eyam
Eyam
Calver
Hassop Baslow
Bakewell
BACKDALE
MINE
010 20 km
012 km
outcrop of
Carboniferous
limestones
Fig. 1.
Map showing the location of the Backdale
Mine.
130
125
35
14
17
26
45
30
17
17
Cravenoceras leion
Marine Band
massive cherty
crinoidal
limestone
bedded
limestone
cm
mudstone
Fig. 2. Columnar section with the position of the Cravenoceras leion
Marine Band at Backdale Mine.
line with wide, symmetric ventrolateral saddle. Adventive
lobe V-shaped, deeper than the external lobe.
Material. Twenty-seven specimens from the Backdale Mine,
between 6 and 49 mm in diameter (Nos LZB 4719, 4720,
4722–4726, 4729, 4731, 4732, 4736–4740, 4743–4745; Zx 2191,
2194, 2196–2200, 2203), have been examined.
Description of the new material
Conch shape.Cravenoceras leion shows that the conch
ontogeny begins with evolute inner whorls, passing an interval
in which the absolute width of the umbilicus increases very
slowly, causing a decrease of the umbilical width/conch diam-
eter ratio, and ending in an adult stage with a reopening of the
umbilicus.
The ontogenetic development of the conch shape can be
observed in a series of specimens. In the smallest specimen of
6 mm diameter (LZB 4744, Fig. 7D), the conch is wheel-
shaped with a wide umbilicus (uw/dm = 0.40) that is bordered
by an angular margin. The venter is very broad.
Larger specimens display the transformation into the adult
morphology. At 15mm diameter (Zx 2194, Fig. 4C), the
umbilicus has a width of only one fifth of the conch diameter,
A WELL-PRESERVED EARLY NAMURIAN AMMONOID FAUNA WITH CRAVENOCERAS LEION 113
WER =
IZR =
dm
(wh-ah)
dm - ah
wh
( )
2
whorl width
(ww)
apertural
height
(ah)
umbilical
width
(uw)
whorl height
(wh)
conch diameter (dm)
external
lobe adventive
lobe
ventrolateral
saddle
median
saddle
Fig. 3. Conch and suture parameters and ratios as used in the descriptions of goniatite species.
Table 1
Dimensions and ratios of specimen Zx 2203 in mm.
dm ww wh uw ah WER ww/dm ww/wh uw/dm IZR
47.72 27.65 22.37 7.81 10.77 1.67 0.58 1.24 0.16 0.52
36.94 23.32 17.54 5.88 8.64 1.70 0.63 1.33 0.16 0.51
28.31 19.29 13.53 4.78 6.21 1.64 0.68 1.43 0.17 0.54
22.10 15.89 9.99 4.32 4.68 1.61 0.72 1.59 0.20 0.53
17.42 12.94 7.78 3.57 3.59 1.59 0.77 1.75 0.22 0.53
13.83 10.63 6.07 3.06 2.87 1.59 0.77 1.75 0.22 0.53
10.96 8.85 4.70 2.84 2.43 1.65 0.81 1.88 0.26 0.48
8.53 7.01 3.42 2.58 1.70 1.56 0.82 2.05 0.30 0.50
6.83 5.39 2.54 2.46 1.33 1.54 0.79 2.13 0.36 0.48
5.50 4.11 1.84 2.34 1.06 1.54 0.75 2.24 0.42 0.42
4.44 2.92 1.33 2.14 0.82 1.51 0.66 2.20 0.48 0.38
3.62 2.08 0.97 1.87 0.65 1.48 0.57 2.14 0.52 0.33
2.97 1.50 0.77 1.16 0.50 1.44 0.50 1.94 0.54 0.35
2.47 1.05 0.59 1.35 0.43 1.47 0.42 1.78 0.55 0.27
2.04 0.83 0.53 1.11 0.40 1.55 0.41 1.55 0.54 0.25
1.64 0.65 0.39 0.89 0.32 1.53 0.39 1.64 0.54 0.20
1.32 0.62 0.36 0.67 0.25 1.52 0.47 1.75 0.51 0.29
1.07 0.57 0.30 0.51 0.23 1.61 0.53 1.92 0.48 0.23
0.85 0.55 0.27 0.31 0.21 1.75 0.64 2.04 0.37 0.23
0.64 0.57 0.27 0.13 0.15 1.69 0.90 2.16 0.20 0.45
0.49 0.60 0.24 0.25 0.49 1.22 2.47
and flanks and venter are broadly rounded. In this ontogenetic
stage, the umbilical margin is rounded. Larger growth stages
display only minor modifications. LZB 4732 (Fig. 4B) shows,
at 25 mm conch diameter, the reappearance of an angular
umbilical margin. At 40 mm diameter (Zx 2191), the flattened
umbilical wall is very steep and bordered by a rectangular
margin against the flanks, which are broadly rounded and
continue into the wide venter. Figure 6 gives an idea of the
variability of conchs of Cravenoceras leion and similar early
cravenoceratids. The chart demonstrates that the conch thick-
ness/diameter ratio is largest at around 15 mm in diameter,
and decreases during ontogeny. At the same time, the relative
width of the umbilicus slightly increases. Only a few specimens
allow measurement of the aperture height, but it is obvious
114 D. KORN & J. W. TILSLEY
Fig. 4. Cravenoceras leion Bisat, 1930 (A–D), and Edmooroceras medusa (Yates 1961) (E–G) from the Backdale Mine. (A) Zx 2191 (coll. J. W. T),
x 1.5. (B) LZB 4732, x 1.5. (C) Zx 2194 (coll. J. W. T), x 2. (D) LZB 4737, x 2.5. (E) Zx 2193 (coll. J. W. T), x 1.5. (F) Zx 2192 (coll. J. W. T),
x 1.5. (G) Zx 2195 (coll. J. W. T), x 4.
Fig. 5. Analysis of conch ontogeny on the basis of a cross section of Cravenoceras leion Bisat 1930; specimen Zx 2203 from the Backdale Mine
(coll. J. W. T.). (A) Cross-section of the complete conch, x 2.5. (B) Development of whorl expansion rate. (C) Development of the imprint
zone width. (D) Cross-sections of each whorl, scaled to the same whorl width for comparison. (E) Development of whorl width (absolute
values plotted). (F) Development of whorl width (ww/dm plotted against absolute dm value). (G) Development of umbilical width (absolute
values plotted). (H) Development of umbilical width (uw/dm plotted against absolute dm value).
A WELL-PRESERVED EARLY NAMURIAN AMMONOID FAUNA WITH CRAVENOCERAS LEION 115
0.1
1
10
100
0.1 1 10 100
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.1 1 10 100
1
10
0
0.
.1
11 10 100
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.1 1 10 100
1
2
3
4
0.1 1 10 100
A
D
E
F
G
B
H
0
0.2
0.4
0.6
0.1 1 10 100
conch diameter (mm)
conch diameter (mm)
conch diameter (mm)
whorl expansion rate
imprint zone width
conch diameter (mm)
conch diameter (mm)
conch diameter (mm)
whorl width (mm)
ww / dm
umbilical width (mm)
uw / dm
C
that the whorl expansion rate (WER), in conchs larger than
40 mm diameter, is constantly around 1.70 (Fig. 5B). The
depth of the imprint zone (IZR) reaches a maximum value of
0.55 (Fig. 5C).
The cross-section of specimen Zx 2203 provides an excellent
insight into the development of conch geometry (Fig. 5A). The
protoconch has a diameter of 0.37 mm and a width of 0.53 mm.
It is embraced by a first whorl with extremely narrow aperture
and crescent-shaped whorl section. After two volutions, at
2.5 mm conch diameter, the whorl section is oval and slightly
depressed. At 3 mm diameter, the whorls again become wider
and, between 3.5 and 8.5 mm conch diameter, whorl width is
more than two times of whorl height. Later in ontogeny, the
whorls are higher again. The umbilicus opens rapidly during
the first four volutions. In growth stages larger than 3.5 mm
the absolute widening decreases, resulting in a relative
closure. A rapid opening of the umbilicus, slightly different on
both sides of the conch, can be seen only in the last volution.
Differences between the ontogenetic stages can best be visual-
ized when all whorl cross-sections are scaled to the same width
(Fig. 5D).
Dimensions of specimen Zx 2203. See Table 1.
Ornament. Shell ornament is rarely preserved in the speci-
mens. Remains of the shell are visible in the dorsal portion of
specimen LZB 4737 (Fig. 4D), where delicate growth lines run
with a wide sinus over the venter. The growth lines are equally
spaced in distances of approximately 0.2 mm. No crenulation
can be traced.
All the specimens larger than 15 mm display prominent
constrictions on the internal cast (Fig. 4A, B). They are irreg-
ularly arranged in distances between 90 and 120°, and are
asymmetrical in their section, with a steep apertural and an
oblique apical side. Undulations are preserved in specimens
larger than 40 mm.
Suture line. During ontogeny, the shapes of lobes and saddles
do not show notable change. The small specimen LZB 4744
displays, at 6 mm conch diameter, a wide and round ventro-
lateral saddle and narrowly rounded prongs of the external
lobe (Fig. 7D). In this stage, the flanks of the external lobe
stand almost parallel. This stage and the next figured stage
(LZB 4737, Fig. 7E) show a wide and pouched adventive lobe.
At 16.7 mm diameter (Zx 2194), the sutural elements are
narrower than in the earlier stages. The external lobe is now
V-shaped with slightly sinuous flanks, and the median saddle
reaches almost 0.4 of the depth of the external lobe (Fig. 7F).
Remarks. Taxonomy of the early cravenoceratids is difficult
if the material is poorly preserved, especially when the onto-
genetic developments of the conch and the suture are not
known. For cravenoceratids with an umbilicus that stagnates
in its widening in pre-adult ontogeny, Korn (1988) proposed
the genus name Emstites with ‘Paraglyphioceras schaelkense
Brüning 1923’ as type species. Included were species such as
E.novalis Korn 1988, Cravenoceras brandoni Palframan 1984
and Cravenoceras leion Bisat 1930, which all share a very
similar ontogenetic development of the conch. Later, the
generic name Emstites was accepted by Kusina (in Kusina &
Yatskov 1999), with the addition of the two equivocal species
E.? obesus and E.tenuor from Novaya Zemlya, and by Titus
(1999), whereas Saunders & Work (1999) regarded it as
junior synonym of Cravenoceras. However, Korn (1988) has
demonstrated that the differences in the sutural ontogeny
(parallel-sided external lobe and lanceolate adventive lobe in
juvenile Cravenoceras, converging external lobe and V-
shaped adventive lobe in juvenile Emstites) justify both
genera.
Emstites schaelkensis and Cravenoceras leion are very
similar species when conch dimensions and ratios are investi-
gated (Fig. 6A), but differences can be seen when larger
populations are compared and, in particular, when the conch
and suture ontogenies are known. C. leion has, in specimens
larger than 35 mm, an umbilicus that is slightly wider (uw/dm
= 0.20–0.25) than in E. schaelkensis (uw/dm = 0.15–0.20).
However, this feature does not allow a clear separation of the
species (Fig. 6B). Furthermore, E. schaelkensis displays dis-
tinct spiral lines on the umbilical margin, which in C. leion are
barely visible. Major differences can be seen in the onto-
genetic development of the suture lines; in large specimens of
C. leion, the adventive lobe is deeper than the external lobe.
The shape of the ventrolateral saddle also differs; in C. leion,
this saddle is almost symmetrical and broadly rounded, even
in juvenile specimens, whereas in E. schaelkensis it is asym-
metrical and very narrow in juveniles (Fig. 7A).
C. brandoni (Palframan 1984) is similar to C. leion in display-
ing a comparable sutural outline in stages up to 18 mm conch
diameter. Of the seven differences cited by Palframan (1984),
only the first two provide useful criteria for separating the two
species, the others are due to the comparison of specimens of
116 D. KORN & J. W. TILSLEY
Cravenoceras leion, Light Clough
Cravenoceras leion, Backdale Mine
Emstites schaelkensis, Schälk
Cravenoceras brandoni, Dowra
0.0
0.2
0.4
0.6
0.8
1.0
1 10 100
0.0
0.1
0.2
0.3
0.,4
0.5
0.6
1 10 100
A
conch diameter (mm)
ww / dm
B
conch diameter (mm)
uw / dm
Fig. 6. Conch ratios whorl width (ww/dm) and umbilical width
(uw/dm) of the early Namurian goniatite species Emstites
schaelkensis (Brüning 1923), Cravenoceras leion Bisat 1930,
and Cravenoceras brandoni Palframan 1984.
different sizes. Even the absence of an angular umbilical
margin in C. brandoni can be seen in intermediate stages of
C. leion, and further investigation is necessary to find clear
reasons to discriminate between the two species.
The difficulties in distinguishing the three species under dis-
cussion demonstrate that more work is needed. Indeed, Bisat
(1950, p. 22) assumed that more than one species had been
included in Cravenoceras leion and, most probably, the
German species E. schaelkensis is present among the strati-
graphically older specimens which were referred by Bisat
(1950) to C. leion.
This discussion demonstrates that the concept of the genus
Emstites (Korn 1988) has to be modified, and that the genus
should be defined with respect to its sutural development,
rather than to conch geometry. Taking this into account, the
species leion and brandoni have to be included in Craveno-
ceras as a consequence of their juvenile sutures which more
closely resemble that of the type species Cravenoceras
malhamense (Bisat 1924).
Family GIRTYOCERATIDAE Wedekind, 1918
Genus EDMOOROCERAS Elias, 1956
Edmooroceras medusa (Yates 1961) (Figs 4E, 8)
1961 Eumorphoceras medusa Yates, p. 54, pl. 6 fig. 1, 2.
1961 Eumorphoceras medusa var. sinuosum Yates, p. 56, pl. 6
fig. 4, 5.
1968 Eumorphoceras medusa Yates; Figge, p. 54, pl. 6 fig. 1.
1968 Eumorphoceras medusa var. sinuosum Yates; Figge,
p. 54, pl. 6 fig. 2.
Holotype. Specimen Doh. 6B. 10; Murchison Museum,
London.
Type locality and horizon. Slieve Anierin, Co. Leitrim,
Ireland; early Namurian, ‘25 ft above an horizon rich in
Cravenoceras leion and Eumorphoceras pseudocoronula’.
Diagnosis.Edmooroceras with discoidal conch (ww/dm =
0.35–0.40) between 10 and 35 mm conch diameter, umbilicus
moderately narrow (uw/dm = 0.25) at 10 mm dm and narrow
(uw/dm 0.10–0.15) in adults. At 35 mm diameter, the venter
becomes oxyconic. Ornament with single ventrolateral spiral
furrow, pronounced umbilical rim. At 20mm dm, ten short
constrictions per whorl. Weak riblets between the constric-
tions. Growth lines biconvex with strong dorsolateral
projection.
Material. Ten three-dimensionally preserved specimens from
the Backdale Mine between 10 and 36 mm conch diameter
(Nos. LZB 4721, 4727, 4730, 4734, 4735; Zx 2192, 2193, 2195,
2201, 2202) have been studied.
Description of the new material
Conch shape.Edm. medusa was previously known from
crushed material. The new material shows that in all growth
stages between 10 and 36 mm, the conch is discoidal (ww/dm
ratio of 0.35–0.40). The venter is rounded, but the large
specimen Zx 2192 indicates that at 35 mm conch diameter, the
venter becomes angular. See Table 2 for dimensions of
samples examined.
Ornament. At 10 mm conch diameter (Zx 2195, Fig. 4G), the
ornament is indistinct and hardly different from similar species
such as Edm. wedekindi (Brüning 1923) and Edm. tornquisti
(Wolterstorff 1899). The spiral furrow is being formed in this
stage, and a prominent umbilical rim can be seen. Four con-
strictions on the flanks form a strong ventrolateral projection.
The venter is free of constrictions. At its greatest diameter
A WELL-PRESERVED EARLY NAMURIAN AMMONOID FAUNA WITH CRAVENOCERAS LEION 117
A
B
C
D
E
F
2 mm 2 mm
1 mm 1 mm
0.5 mm 0.5 mm
Fig. 7. Ontogenetic development of the suture lines in Emstites schaelkensis (Brüning 1923) from Schälk, Rhenish Massif, Germany, and
Cravenoceras leion Bisat 1930 from the Backdale Mine, Derbyshire. (A) Emstites schaelkensis (Brüning 1923), specimen WMN 10196, at
ww =6.2 mm, wh = 3.5 mm; x 16. (B) Emstites schaelkensis (Brüning 1923), specimen WMN 10197, at ww =12.5 mm, wh = 5.9 mm; x 8.
(C)Emstites schaelkensis (Brüning 1923), specimen WMN 10199, at dm = 20.4 mm, ww =16.3 mm, wh = 11.2mm; x 6. (D)Cravenoceras
leion Bisat 1930 specimen LZB 4744, at dm = 5.8 mm, ww = 4.2 mm; x 20. (E) Cravenoceras leion Bisat, 1930, specimen LZB 4737, at dm =
11.4 mm, ww =10.4 mm; x 10. (F) Cravenoceras leion Bisat 1930 specimen Zx 2194 from, at dm = 16.7 mm, ww = 12.4 mm; x 6.
(13 mm), the specimen shows a modification of the ornament:
the constrictions become shorter and form a weak dorsolateral
salient. Between the constrictions, three to five weak riblets
can be traced.
In the larger specimen Zx 2193 (Fig. 4E), the trend towards
shorter constrictions is maintained and, at 20 mm diameter,
they are restricted to the inner flank. They are here more
densely arranged, six per half volution, and are convex
towards the aperture. In their interspaces, weak riblets can
be seen which are strongly biconvex and continue without
decrease of their strength over flanks and venter. The smooth
umbilical rim and the ventrolateral groove are most prominent
in this growth stage.
Zx 2192 (Fig. 4F) is the largest specimen of the suite, it
shows that at 30 mm conch diameter the ventrolateral groove
disappears. From there on, the conch is smooth without
constrictions.
Suture line. This is typical for girtyoceratid ammonoids, at
26.8 mm diameter (Zx 2192; Fig. 8), it shows an asymmetric
ventrolateral saddle which in its size is the dominant element
of the suture line.
Remarks. Many species of Edmooroceras are very similar
and can only be separated in intermediate growth stages.
Edm. medusa belongs to the weakly ribbed species of the
genus with single ventrolateral spiral groove, and hence
cannot be confused with Edm. plummeri(Miller & Youngquist
1948), Edm. pseudocoronula (Bisat 1950), Edm. bisati (Horn
1960), Edm. tenuicostatum (Titus 1999), and Edm. tornquisti
(Wolterstorff 1899).
The stratigraphically older Edm. wedekindi does not show
riblets in the interspaces of the constrictions and has growth
lines with a much shallower dorsolateral sinus. Edm. stubble-
fieldi (Moore 1946) has a very faint spiral groove and becomes
acute at 14 mm diameter. Also similar are Edm. postmesleri-
anum (Brüning 1923) and Edm. weetsense (Moore 1946), but
these species have fewer and much weaker constrictions. It is
not clear if it is really possible to separate Yates’ var. sinuo-
sum, since the larger number of constrictions in this form may
only represent intraspecific variability.
Genus GIRTYOCERAS Wedekind, 1918
Girtyoceras sp. indet.
Material. Only two small specimens of 7 and 13 mm conch
diameter (Nos. LZB 4741, 4742) are available. The larger of
these, LZB 4742, is an almost smooth lenticular conch with
rounded venter and angular umbilical margin. The material
does not allow assignment to any species of the genus.
Remarks. The genus Girtyocerasis rare in the early Namurian
rocks of Europe. Korn (1988, p. 62) described similar speci-
mens in open nomenclature from the basal Namurian of the
Rhenish Massif.
3. STRATIGRAPHICAL IMPLICATIONS
Understanding of the stratigraphy of the earliest Namurian in
the Rhenohercynian and Subvariscan sedimentary realms is
hindered by the lack of adequate sections with sufficient
numbers of well preserved ammonoid index species. Calver &
Ramsbottom (in Earp et al. 1961) summarized the goniatite
stratigraphy of the Upper Bowland Shales in the Clitheroe
district, Lancashire. Following Bisat (1950), they distinguished
three faunal horizons within the E1a Zone, of which the lower
two contain ‘Cravenoceras leion’. They regarded the type
horizon of the species at Light Clough as its lowest occurrence.
Yates (1962, p. 368) discovered a succession of goniatite
faunas within the Pendleian of County Leitrim, Ireland, and
showed that, within the E1a Zone (i.e. ‘Cravenoceras leion
Zone’), at least three faunal bands can be distinguished.
The lowest contains ‘Eumorphoceras rota (Yates 1961)’
(= Cousteauceras (?) involutum (Horn 1960)) and ‘Eumor-
phoceras pseudocoronula’, the second ‘Eumorphoceras
pseudobilingue A’ (= Edmooroceras bisati (Horn 1960)), and
a third ‘Eumorphoceras medusa’. ‘Cravenoceras leion’ was
found only in the lower two bands.
Horn (1960) and Figge (1968) described sections within the
Visean–Serpukhovian transition beds and the earliest
Namurian of the Rhenish Massif. They found that the succes-
sion closely resembles the Irish zonation, and Korn (1988)
revised the goniatite species from these horizons. In propos-
ing a revised goniatite stratigraphy for the basal Namurian,
Korn & Horn (1997) showed that at least seven goniatite
zones, all based on eumorphoceratids, can be distinguished
within the Pendleian. They introduced an Edm. medusa Zone
for the strata above the beds containing a rather diverse fauna
including Edm. pseudocoronula, Edm. tornquisti, Edm. bisati,
and Coust. (?) involutum. The goniatite fauna from Backdale
Mine, described in this paper, can be assigned to the
Edmooroceras medusa Zone.
Acknowledgements. We are indebted to Nick Riley (British Geo-
logical Survey, Nottingham) for revising the typescript and for his
helpful suggestions. We also thank Wolfgang Gerber (Tübingen) for
producing the digital images shown in Figure 4. The paper profited
much from the comments of two anonymous reviewers.
118 D. KORN & J. W. TILSLEY
2 mm
Fig. 8. Suture line of Edmooroceras medusa (Yates 1961), specimen
Zx 2192 from the Backdale Mine, at dm =26.8 mm, ww =
17.8 mm; x 3.
Table 2
Dimensions (mm) and ratios of specimens of Edmooroceras medusa
(Yates 1961).
Specimen No. dm ww wh uw ww/dm ww/wh uw/dm
Zx 2192 36.0 13.4 21.2 – 0.37 0.63 –
Zx 2192 27.2 10.3 – – 0.38 – –
Zx 2193 20.4 – 9.9 3.8 – – 0.19
Zx 2195 13.8 5.7 6.9 3.0 0.41 0.83 0.22
Zx 2201 12.1 5.1 5.3 2.8 0.42 0.96 0.23
REFERENCES
AITKENHEAD, N., CHISHOLM, J. I. & STEVENSON, I. P. 1985. Geology of
the Country Around Buxton, Leek and Bakewell. Memoir of
the British Geological Survey, England and Wales, Sheet 111.
BISAT, W. S. 1924. The Carboniferous goniatites of the north of
England and their zones. Proceedings of the Yorkshire Geo-
logical Society, 20, 40–124.
BISAT, W. S. 1928. The Carboniferous goniatite zones of England and
their continental equivalents. Compte Rendu Congrès Inter-
national de Stratigraphie et de Géologie du Carbonifère
(Heerlen 1927), 117–133.
BISAT, W. S. 1930. On Cravenoceras leion, the basement goniatite of
the Upper Carboniferous. Transactionsofthe Leeds Geological
Association,Part 20, 28–32.
BISAT, W. S. 1950. The junction faunas of the Visean and Namurian.
Transactions of the Leeds Geological Association, 6, 10–26.
BRANDON, A., RILEY, N. J., WILSON, A. A. & ELLISON, R. A. 1995.
Three new early Namurian (Elc–E2a) marine bands in central
and northern England, UK, and their bearing on correlations
with the Askrigg Block. Proceedings of the Yorkshire Geo-
logical Society, 50, 333–355.
BRÜNING, K. 1923. Beiträge zur Kenntnis des Rheinisch-westfälischen
Unterkarbons, insbesondere der Goniatiten und Korallen in der
stratigraphischen Stellung und Gliederung. Marburg, 1–59.
CALVER, M. A. & RAMSBOTTOM, W. H. C. 1961. Stratigraphical
palaeontology. In: EARP, J. R., MAGRAW, D., POOLE, E. G.,
LAND, D. H. & WHITEMAN, A. J. (eds) Geology of the Country
aroundClitheroe and Nelson. Memoir of the Geological Survey
of Great Britain, England and Wales, Sheet 68, 174–207.
ELIAS, M. K. 1956. Upper Mississippian and lower Pennsylvanian
formations of south-central Oklahoma. In: Petroleum Geology
of Southern Oklahoma. American Association of Petroleum
Geologists, Tulsa, Oklahoma, 56–134.
FIGGE, K. 1968. A Goniatite fauna from the Visean/Namurian bound-
ary. Palaeontology,11, 264–274.
GILL, W. D. 1947. On the Upper Bowland Shales in Carla Beck, near
Skipton, Yorkshire. ProceedingsoftheLeedsPhilosophicaland
Literary Society, 5, 60–64.
HORN, M. 1960. Die Zone des Eumorphoceras pseudobilingue im
Sauerland. Fortschritte in der Geologie von Rheinland und
Westfalen, 3, 303–342.
JOHNSON, G. A. L., HODGE, B. L. & FAIRBAIRN, R. A. 1962. The base
of the Namurian and of the Millstone Grit in north-eastern
England. Proceedings of the Yorkshire Geological Society, 33,
341–362.
KORN, D. 1988. Die Goniatiten des Kulmplattenkalkes (Cephalopoda,
Ammonoidea; Unterkarbon; Rheinisches Schiefergebirge).
Geologie und Paläontologie in Westfalen, 11, 1–293.
KORN, D. 2000. Morphospace occupation of ammonoids over
the Devonian–Carboniferous boundary. Paläontologische
Zeitschrift, 74, 247–257.
KORN, D. & HORN, M. 1997. Subdivision of the basal Early Namurian
(Early Carboniferous) in the Rhenish Massif (Germany).
Newsletters on Stratigraphy, 35, 115–126.
KUSINA, L. F. & YATSKOV, S. V. 1999. Nizhne- i srednekame-
nougol’nye ammonoidei Novoy Zemli. Trudy Paleontologich-
eskogo Instituta Rossiiyskaya Akademiya Nauk, 275, 1–144.
MILLER, A. K. & YOUNGQUIST, W. 1948. The cephalopod fauna of the
Mississippian Barnett Formation of Central Texas. Journal of
Paleontology, 22, 649–671.
MOORE, E. W. J. 1946. The Carboniferous Goniatite Genera Girty-
oceras and Eumorphoceras. Proceedings of the Yorkshire Geo-
logical Society, 25, 387–445.
PALFRAMAN, D. F. B. 1984. A new species of Cravenoceras from the
Namurian of County Leitrim, Ireland. Bulletin of the Geo-
logical Survey of Ireland, 3, 211–219.
RUZHENCEV, V. E. 1957. Filogeneticheskaya sistema paleozoyskikh
ammonoidey. Byulleten’ Moskovskogo obshchestva ispytately
prirody, novaya seriya, otdel geologicheskiy, 31, 49–64.
SAUNDERS, W. B. & WORK, D. M. 1999. The Cravenoceras-Glaphyrites
dilemma: ammonoid sutures vs. shell shape in the Mid-
Carboniferous. In: ROZANOV, A. YU. & SHEVYREV, A. A.
(eds) Iskopaemye tsefalopody: Noveyshie dostizheniya v ikh
izuchenii, Rossiyskaya akademiya nauk. Paleontologicheskiy
Institute, Moskva, 125–137.
STEPHENS, J. V., MITCHELL, G. H. & EDWARDS, W. 1953. Geology of
the country between Bradford and Skipton. Memoir of the
Geological Survey of Great Britain, England and Wales, Sheet
69.
TITUS, A. L. 1999. Ammonoid biostratigraphy of the Barnett Shale
(Late Mississippian), Texas, USA. In: ROZANOV, A. Yu. &
SHEVYREV, A. A. (eds) Iskopaemye tsefalopody: Noveyshie
dostizheniya v ikh izuchenii, Rossiyskaya akademiya nauk.
Paleontologicheskiy Institut, Moskva, 155–168.
WEDEKIND, R. 1918. Die Genera der Palaeoammonoidea Goniatiten).
Mit Ausschluß der Mimoceratidae, Glyphioceratidae und
Prolecanitidae. Paläontographica, 62, 85–184.
WOLTERSTORFF, W. 1899. Das Untercarbon von Magdeburg-Neustadt
und seine Fauna. Jahrbuch der Königlich Preußischen Geolo-
gischen Landesanstalt und Bergakademie, 19 (for 1898), 3–64.
YATES, P. J. 1961. New Namurian goniatites of the genus Eumorpho-
ceras. Palaeontology, 4, 54–58.
YATES, P. J. 1962. The Palaeontology of the Namurian rocks of Slieve
Anierin, Co. Leitrim, Eire. Palaeontology, 5, 355–443.
Revised manuscript received: 5th April 2002
A WELL-PRESERVED EARLY NAMURIAN AMMONOID FAUNA WITH CRAVENOCERAS LEION 119
