Brachiopods from the Sanadinovo Formation (Lower Cenomanian) in northern Bulgaria

Abstract

Brachiopod faunas from the Early Cenomanian Sanadinovo Formation in northern Bulgaria comprise seven species in five genera, namely Cyclothyris sp., Concinnithyris subundata (J. Sowerby), Terebratulina imbricata Owen, T. etheridgei Owen, Terebratulina sp., Kingena concinna Owen and Modestella geinitzi (Schloenbach). With the exception of Cyclothyris, all are recorded for the first time from the Upper Cretaceous of Bulgaria; the present records extend the geographic distribution of these taxa from England, northern France and Poland to central-northern Bulgaria, which, during the Late Cretaceous, was situated along the southern margin of the North European epicontinental sea.

Full text

Brachiopods from the Sanadinovo Formation
(Lower Cenomanian) in northern Bulgaria
Maria Aleksandra Bitner
a,
*, Neda Motchurova-Dekova
b
a
Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/55, PL-00-818 Warszawa, Poland
b
National Museum of Natural History, 1, Tzar Osvoboditel bul, BUL-1000 Sofia, Bulgaria
Received 28 June 2004; accepted in revised form 16 February 2005
Available online 12 September 2005
Abstract
Brachiopod faunas from the Early Cenomanian Sanadinovo Formation in northern Bulgaria comprise seven species in five
genera, namely Cyclothyris sp., Concinnithyris subundata (J. Sowerby), Terebratulina imbricata Owen, T. etheridgei Owen,
Terebratulina sp., Kingena concinna Owen and Modestella geinitzi (Schloenbach). With the exception of Cyclothyris, all are recorded
for the first time from the Upper Cretaceous of Bulgaria; the present records extend the geographic distribution of these taxa from
England, northern France and Poland to central-northern Bulgaria, which, during the Late Cretaceous, was situated along the
southern margin of the North European epicontinental sea.
Ó2005 Elsevier Ltd. All rights reserved.
Keywords: Brachiopods; Cyclothyris;Concinnithyris;Terebratulina;Kingena;Modestella; Lower Cenomanian; Sanadinovo Formation; Northern
Bulgaria
1. Introduction
Brachiopods are commonly found in strata of
Cenomanian age across Europe, and brachiopod studies
have a long tradition, dating back to the nineteenth
century (e.g., J. Sowerby, 1812e1822; de Lamarck, 1819;
J. de C. Sowerby, 1822e1846; Roemer, 1841; d’Archiac,
1847; Davidson, 1852e1853, 1874; Schloenbach,
1866a,b, 1867; Quenstedt, 1868e1871). Subsequent
authors both revised and provided additional records
of Cenomanian brachiopod taxa from western and
central Europe. Reference is here made to papers by
Sahni (1929), Pettitt (1950, 1954), Owen (1962, 1968,
1970, 1978, 1988), Popiel-Barczyk (1972, 1977), Calzada
and Peyberne
`s (1978), Gaspard (1978, 1988, 1997),
Bilinkevich and Popiel-Barczyk (1979) and In
˜esta and
Calzada (1996).
In contrast to the rest of Europe, studies of bra-
chiopods from Bulgaria are few. Zacharieva-Kova
ceva
(1947) was the first to provide systematic descriptions
of Late Cretaceous (Cenomanian, Turonian and
‘‘Senonian’’) and Early Cenozoic (Danian) taxa.
Unfortunately, she did not study the internal characters
of the 32 species [including Concinnithyris bulla (So-
werby) and Terebratulina striata (Wahlenberg)] in her
collection, which is now lost. Most forms were assigned
to Terebratula and Rhynchonella, and the entire material
came from ill-defined stratigraphic horizons and local-
ities.
The first modern studies, also comprising examination
of internal features, of Late Cretaceous brachiopods
from Bulgaria were carried out by Motchurova-Dekova
* Corresponding author.
E-mail address: bitner@twarda.pan.pl (M.A. Bitner).
0195-6671/$ - see front matter Ó2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cretres.2005.02.008
www.elsevier.com/locate/CretRes
Cretaceous Research 26 (2005) 525e539

(1994, 1995, 1996, 1997). The present paper continues
this work and deals with assemblages from the Early
Cenomanian Sanadinovo Formation, as exposed near
the village of Novachene (northern Bulgaria; Fig. 1).
With the exception of Cyclothyris sp., all brachiopod
species are recorded for the first time from Bulgaria. For
some of them, the present records are the first from
beyond the type localities in Great Britain.
2. Geological setting
The material studied was collected near the village
of Novachene (Pleven district), on the east bank of the
River Osam (Fig. 1), from an outcrop exposing the
lowermost portion of the type section of the Sanadinovo
Formation. North of the villages of Novachene and
Sanadinovo, Cenomanian strata are represented by marls
intercalated with thin-layered marly limestones (Sanadi-
novo Formation; see Jolki
cev, 1987), and overlying
coarse-grained, glauconitic sandstones of the upper
Dekov Formation (Ivanov and Stoykova, 1990)of
Late Albian age (Stoliczkaia dispar Zone; see Ivanov
et al., 1980)(Fig. 2). Both the Lower/Upper Cretaceous
boundary and Cenomanian lithological succession were
described in detail by Jolki
cev et al. (1988); bed numbers
in Fig. 2 are those proposed by these authors.
A sudden lithological change to marls marks the base
of the Sanadinovo Formation. Brachiopods are confined
to Bed 5, which is 7 m thick (Fig. 2), and consists of grey-
whitish marls, with some quartz and glauconite in the
lower part. From this bed, Jolki
cev (1987) and Jolki
cev
et al. (1988) recorded abundant serpulids (‘‘Serpula’’
proteus Sowerby) and belemnites [Neohibolites ultimus
(d’Orbigny), N. ultissimus Stojanova-Vergilova, N. aff.
stilus Branford, N. submedius Swinnerton and
N. menjailenkoi Gustomesov] as well as rare inoceramids
(Inoceramus crippsi Mantell). Previously, Nachev and
Nikolov (1961) and Nikolov and Nachev (1962) had
listed the ammonites Mantelliceras mantelli (J. Sowerby),
Mantelliceras martimpreyi (Coquand), and the echinoid
Discoidea cylindrica (de Lamarck) (ZCamerogalerus
cylindricus) from correlative strata in the Pleven district.
Unfortunately, the ammonite material recorded by these
authors is now lost. In a recent, comprehensive study of
R o m a n i a
Y
ug
os
l
a
v
i
a
B U L G A R I A
M a c e d o n i a
B
l
a
c
k
S
e
a
B
A
B
PLEVEN brachiopod locality
Upper Cretaceous
outcrops
Osam
Danube
Nikopol
Zhernov
Debovo
Novachene
Sanadinovo
Muselievo
Vit
05 km
G
r
e
e
c
e
T
u
r
k
e
y
N
Fig. 1. Sketch map of southeast Europe, showing Bulgaria (A) and the
study area (B) in more detail, and the extent of Upper Cretaceous
deposits.
Albian Cenomanian Stage
Upper Lower Substage
Stoliczkaia
dispar Mantelliceras mantelli Ammonite zone
Thalmanninella appenninica appenninica
Foraminifera zone
Eiffelithus turriseiffeli Lithraphidites acutum Nannofossil zone
Litosphaeridium siphoniphorum
Dinocyst zone
Dekov Fm Sanadinovo Fm Formation
Lithological
column
Brachiopod
taxa
Bed number
(thickness)
Concinnithyris
subundata
Terebratulina
imbricata
Terebratulina
etheridgei
Kingena
concinna
Modestella
geinitzi
Cyclothyris sp.
Terebratulina sp.
Marls Glauconitic sandstones
5
(7m)
4
(2.3m)
Fig. 2. Section exposed near the village of Novachene, with ammonite,
foraminiferal, nannofossil and dinocyst zones indicated; note that
documentation of the Mantelliceras mantelli Zone could not be
confirmed in a recent paper by Kennedy and Jolki
cev (2004).
526 M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Middle Cenomanian ammonites, Kennedy and Jolki
cev
(2004) were unable to confirm the presence of the
Mantelliceras mantelli Zone in the lowest portion of the
Sanadinovo Formation. However, according to Jolki
cev
et al. (1988) and Stojanova-Vergilova (pers. comm.
2004), the belemnite assemblage (see above) clearly
indicates an Early Cenomanian age for Bed 5.
Microfossil studies by Jolki
cev et al. (1988) document
the Thalmanninella appenninica appenninica foraminifer-
al zone, while Sinnyovski and Shumenko (1988) recorded
the Eiffelithus turriseiffeli nannoplankton zone, and
Pavlishina (1990) described the Litosphaeridium siphon-
iphorum dinocyst zone from the section exposed at
Novachene. These three zones also encompass the higher
portion of the underlying Dekov Formation (Fig. 2).
3. Material and methods
The majority of the material (206 specimens in total)
described below was hand-picked from the Novachene
section, while a portion of the micromorphic forms was
isolated from three bulk samples (about 5 kg each) sieved
at a mesh width of 0.5 mm. Preservation varies consid-
erably; although most specimens (87%) are articulated,
many are damaged and/or crushed, and others decorticated.
Serial sections were made using a Croft apparatus;
acetate peels were prepared as well. Samples selected for
study of shell ultrastructure were embedded in epoxy
resin, cut and polished, then etched with 5% HCl before
coating with platinum for observation under the
scanning electron microscope (SEM).
The majority of the collection (including all illustrated
specimens) is housed in the National Museum of
Natural History in Sofia (registration numbers NMNHS
31070e31075). Five specimens of Terebratulina imbri-
cata, plus material used for ultrastructural investiga-
tions, are kept at the Institute of Paleobiology, Polish
Academy of Sciences, Warszawa, under collection
number ZPAL Bp.52.
Abbreviations. L, length; W, width; T, thickness;
NMNHS, National Museum of Natural History, Sofia;
NHM, The Natural History Museum, London; ZPAL,
Institute of Paleobiology, Warszawa.
4. Systematic palaeontology
Order: Rhynchonellida Kuhn, 1949
Superfamily: Hemithiridoidea Rzhonsnitskaia, 1956
Family: Cyclothyrididae Makridin, 1955
Subfamily: Cyclothyridinae Makridin, 1955
Genus Cyclothyris M’Coy, 1844
Type species.Terebratula latissima J. de C. Sowerby,
1840, by subsequent designation of Buckman (1906,
p. 326).
Cyclothyris sp.
Fig. 3I, J
Material. Four crushed specimens (NMNHS 31070).
Dimensions. These poorly preserved specimens can-
not be adequately measured. The best-preserved and
largest specimen, here illustrated, lacks the umbo. Its
length would have been in excess of 20 mm; the width, as
preserved, is 23.5 mm, while the thickness cannot be
determined on account of deformation.
Description. Medium-sized, subpentagonal, unipli-
cate and multicostate Cyclothyris, with O40 relatively
sharp ribs on each valve. Several faint growth lines can
be traced on anterior portion of valves. Deltidial plates,
visible in a single specimen, form wing-like extension
around medium-sized foramen.
Remarks. External features show these specimens to
be assignable to Cyclothyris, but specific attribution is
impossible. The ornament suggests some similarity to
members of the group of Cyclothyris latissima. Two
other Cenomanian species of Cyclothyris,C. difformis
(Valenciennes, in de Lamarck, 1819) and C. compressa
(Valenciennes, in de Lamarck, 1819) have fewer, yet
stronger ribs (Owen, 1962).
Occurrence.Cyclothyris has been recorded from the
AptianeMaastrichtian across Europe. Previous records
from Bulgaria refer to the Cenomanian at Dobreva
Chuka (northeast Bulgaria; see Motchurova-Dekova,
1995, 1997).
Order: Terebratulida Waagen, 1883
Suborder: Terebratulidina Waagen, 1883
Superfamily: Terebratuloidea Gray, 1840
Family: Gibbithyrididae Muir-Wood, 1965
Subfamily: Gibbithyridinae Muir-Wood, 1965
Genus Concinnithyris Sahni, 1929
Type species.Terebratula obesa J. de C. Sowerby,
1823, by original designation of Sahni (1929, p. 11).
Concinnithyris subundata (J. Sowerby, 1813)
Figs. 3AeH, 4, 5
v. 1813 Terebratula subundata J. Sowerby, p. 47, pl. 15,
fig. 7.
1929 Concinnithyris subundata (J. Sowerby); Sahni,
p. 17, pl. 1, figs. 10e16 (non 17); pl. 8, figs.
11, 12.
527M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

1929 Concinnithyris burhamensis Sahni, p. 16, pl. 2,
figs. 8e13; pl. 8, figs. 22, 23.
1983 Concinnithyris burhamensis Sahni; Cooper,
p. 184, pl. 24, figs. 18e22.
v. 1988 Concinnithyris subundata (J. Sowerby); Owen,
p. 132, pl. 6, figs. 16e18; pl. 15, figs. 4e18; pl. 16.
1997 Concinnithyris subundata (J. Sowerby); Gaspard,
p. 150, pl. 1, fig. 19.
Fig. 3. Early Cenomanian brachiopods from the Sanadinovo Formation (northern Bulgaria), with the exception of H. AeC, Concinnithyris
subundata, dorsal, lateral and anterior views of NMNHS 31071-5; !3; DeG, Concinnithyris subundata, ventral, dorsal, lateral and anterior views of
NMNHS 31071-11; !2. H, Concinnithyris subundata, inner view of dorsal valve to show loop and cardinalia, Turonian, Blue Bell Hill, Burham
(Kent, Great Britain), NHM 15198 (photograph courtesy of the NHM, London); !2. I, J, Cyclothyris sp., ventral and dorsal views of NMNHS
31070-1; !2. KeN, Kingena concinna, ventral, dorsal and lateral views of NMNHS 31074-1, !4, and enlarged portion of dorsal valve to show
pustules on the surface; !16. OeQ, Kingena concinna, ventral, dorsal and lateral views of NMNHS 31074-2; !4.
528 M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Material. Twenty-seven articulated specimens and
numerous fragments (NMNHS 31071), all of them in
part compressed or broken.
Dimensions (in mm)
Description.External morphology. Medium-sized
shell (L
max
, 27.5 mm; L
min
, 7.3 mm), ventribiconvex.
Outline variable, from subcircular to subpentagonal or
elongate-oval. Maximum width at about mid-length;
maximum thickness in posterior third. Beak ridges
short, rounded, distinct only posteriorly. Umbo suberect
to incurved with an epithyrid, subcircular foramen of
medium to large size. Symphytium not exposed.
Anterior commissure rectimarginate to slightly unipli-
cate. Lateral commissures of most specimens apparently
straight but deformed by compaction, possibly anteri-
orly curved towards dorsal valve. Shell surface marked
by well-developed growth lines.
Internal morphology. One dorsal valve (not illustrated)
was prepared to expose the loop; this is short with a wide
transverse band in the form of a moderately elevated arch.
Specimen # L W T W/L T/L
NMNHS 31071
1 (6104) 25.4 25.0 12.7 0.98 0.50
3 19.7 20.0 e1.01 e
5 10.8 11.2 6.8 1.03 0.63
7 10.6 10.3 5.8 0.97 0.55
11 18.2 17.7 11.4 0.97 0.63
14 12.2 13.0 6.7 1.06 0.55
16 10.6 10.5 5.0 0.99 0.47
21 15.3 13.4 7.6 0.87 0.50
Note: nearly all measurements are approximate owing to poor
preservation.
Fig. 4. Transverse serial sections through the umbo of Concinnithyris subundata (NMNHS 31071-8), Novachene, Sanadinovo Formation (Lower
Cenomanian): L, 15.7 mm; W, 16.0 mm; T, 9 mm. Distance from the ventral umbo given in mm.
529M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Crural processes short and bluntly pointed; cardinalia
broken. Shape of loop consistent with that observed in
material from Great Britain (Fig. 3H). One specimen was
sectioned (Fig. 4); internal characters obscured by de-
formation, and not shown in Fig. 4. A pedicle collar is
noted in ventral valve (see Fig. 4, sections 0.3 to 0.85).
Cardinal process poorly developed. Socket ridges shallow.
Hinge plates short, ventrally convex. Crural processes
high, tapering, inwardly curving, low-arched transverse
band with shallow sulcus posteriorly, noted in thin section
(see Fig. 4, section 4.8), but not on dissected loop.
Shell ultrastructure. Two sections were studied under
SEM: one longitudinal through the middle of the ventral
valve and a second transverse through the umbo (Fig. 5).
Fig. 5. SEM micrographs of Concinnithyris subundata from near Novachene, Sanadinovo Formation (Lower Cenomanian). A, B, longitudinal
section at centre of ventral valve (ZPAL Bp.52/7); with A representing the entire shell thickness; external surface on the right, primary layer in the
lower right-hand corner. On the right, two layers of secondary fibres interlayered with tertiary prisms building the main thickness of the shell, two
thinner layers of secondary fibres are seen on the left; B represents a portion of shell, close to the external surface. Recrystallised primary layer on the
right, followed by two layers of secondary fibres and two of tertiary fibres. Two punctae filled with recrystallised calcite. C, D, cross sections of the
umbonal part (ZPAL Bp.52/8), with C representing a ventral valve, entire shell thickness, penetrated by punctae. Lateral portion of ventral valve to
the left; note increase in thickness of the tertiary sublayers towards the shell centre; D shows the dorsal umbo, cardinal process (c.p.) and incipient
hinge plates (h.p.). E, F, transverse sections of the entire shell showing secondary and tertiary layers, visible modifications of fibres near punctae
(ZPAL Bp.52/9). Scale bars represent 200 mm (A, C, D), 100 mm (B, E) and 50 mm (F).
530 M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Shell relatively thick (maximum 2000 mm), composed
of three layers: primary, secondary fibrous and tertiary
prismatic. The presence of three layers is a characteristic
feature of Concinnithyris (MacKinnon and Williams,
1974). The primary layer (30e70 mm thick) is probably
recrystallized, composed of rather poorly differentiated
crystallites, almost perpendicular to shell surface.
Remaining part of shell composed of alternation of
several layers of secondary fibrous calcite and tertiary
prismatic calcite. Fibres of secondary layer well
preserved, while prisms of tertiary layers appear
recrystallized. In posterior part of shell, 3e5 layers of
secondary fibres alternate with 3e4 layers of tertiary
prismatic calcite (Table 1).
It is noted that tertiary layer thickness increases from
the lateral to the central part of the shell in transverse
section. Secondary layer fibres are usually subparallel to
the shell long axis. In cross sections they have an anvil-
like shape. Density of punctae, which penetrate the
whole thickness of the shell, is 100e150/mm
2
in the
cross section of the ventral umbo (Fig. 5C).
Remarks. In outline and umbonal characters, the
Bulgarian material matches well that assigned to
Concinnithyris subundata by Owen (1988), who consid-
ered C. burhamensis to be a synonym. However, British
and French representatives of this species grow to
a quite large size (L
max
, 39.4 mm; L
min
, 25.4 mm; Owen,
1988, p. 134), while the material studied here is much
smaller. The posterior part of the specimen sectioned for
the present study (Fig. 4) is poorly preserved and crural
bases are not clearly seen. However, the rest is entirely
similar to sections of C. subundata illustrated by Owen
(1988, fig. 25), especially with regard to the inwardly
concave, descending branches and the wide transverse
band with a shallow sulcus posteriorly.
Occurrence. Cenomanian of Great Britain and
France, Turrilites acutus Subzone and part of the
Acanthoceras jukesbrownei Zone (Gaspard, 1997); Lower
Cenomanian of northern Bulgaria.
Superfamily: Cancellothyridoidea Thomson, 1926
Family: Cancellothyrididae Thomson, 1926
Subfamily: Cancellothyridinae Thomson, 1926
Genus Terebratulina d’Orbigny, 1847
Type species.Anomia retusa Linnaeus, 1758,by
subsequent designation of Brunton et al. (1967, p. 176).
Terebratulina imbricata Owen, 1988
Figs. 6e9
v. 1988 Terebratulina imbricata Owen, p. 148, pl. 22,
figs. 1e4.
Material. One hundred and twenty-five articulated
specimens, plus 14 ventral and 13 dorsal valves (NMNHS
31072; ZPAL Bp.52/1-6).
Dimensions (in mm; see also Fig. 6)
Description.External morphology. Shell very small
(L
max
, 5.0 mm) and variable in outline, from circular to
subtriangular and elongate oval; younger specimens
usually more circular. Maximum width situated in
anterior third in adults. Shell ventribiconvex; however,
shell convexity may vary, from near-equally biconvex
with both valves strongly convex to a clearly more
convex ventral valve. Ornament consists of ribs, in-
creasing in number through bifurcation and/or in-
tercalation, from 7e8 in specimens 1.2 mm long to 30
in adults. Growth lines numerous, lamellose, of imbri-
cate character typical of this species (see Fig. 8H).
Additionally, entire shell surface covered in small,
rounded pustules. Beak and foramen vary during
ontogeny. In juveniles, beak is erect, becoming curved
with growth. Foramen moderately large, submesothyrid
in young specimens, becoming small, mesothyrid to
permesothyrid in adults. Deltidial plates small, tri-
angular, disjunct. Anterior commissure rectimarginate.
Internal morphology. Internal characters have been
studied for the first time for this species. Ventral valve
with massive teeth, and two deep grooves beneath teeth
to accommodate tall, inner socket ridges. No dental
plates present. Pedicle collar present. Dorsal valve with
deep dental sockets. Inner socket ridges short but very
tall, extending beyond hinge margin. Cardinal process
indistinct, forming small depression. Crura short and
thick. Loop forms a ring with a low but distinct
elevation in anterior part (Fig. 8A, B). Internal margins
of both valves strongly crenulated.
Table 1
Thickness of calcite layers in Concinnithyris subundata (in mm)
pr.l. 1st s. 1st t. 2nd s. 2nd t. 3rd s. 3rd t. 4th s. 4th t. 5th s.
spot 1 68 80 51 119 416 42 122 30 40 e
spot 2 35 55 41 37 333 40 390 30 113 102
pr.l., primary layer; s., secondary layer; t., tertiary layer.
Specimen # L W T W/L T/L
NMNHS 31072
11 5.0 4.3 3.1 0.86 0.62
5 4.9 3.9 3.3 0.80 0.67
12 4.5 4.0 3.0 0.89 0.67
2 3.6 3.5 2.2 0.97 0.61
13 4.2 3.8 2.9 0.90 0.69
531M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Shell ultrastructure. Two transverse sections through
mid-shell length were studied under SEM: one of a dorsal,
the other of a ventral valve. This revealed no difference in
shell ultrastructure. Shell composed of two calcite layers,
primary and secondary. Maximum shell thickness on the
rib is 350e450 mm; minimum shell thickness 200e
220 mm in the sulcus. Primary layer relatively thicker in
the ribs (60e70 mm) and thinner in the sulcus (20e
25 mm), composed of microcrystalline calcite. Fibres
have peculiar symmetrical orientation in the ribs
(Fig. 9AeC).
Remarks. Until now, this species was known only
from the Cenomanian of Great Britain (Owen, 1988).
The extremely well-preserved and rich material from
Bulgaria allows conclusions to be drawn on the range of
variation and ontogenic changes, as well as on internal
structures and shell ultrastructure.
Terebratulina imbricata is the commonest species
(O150 specimens) in the collection available. Externally,
our specimens fully correspond to material from Great
Britain, described and illustrated by Owen (1988);
however, they are slightly smaller. On account of the
characteristic imbricate growth lines, T. imbricata is
easily distinguished from congeners.
Occurrence. Cenomanian of Great Britain; Lower
Cenomanian of northern Bulgaria.
Terebratulina etheridgei Owen, 1988
Fig. 10LeO
v. 1988 Terebratulina etheridgei Owen, p. 147, pl. 5,
fig. 17; pl. 19, figs. 1, 2; pl. 21, figs. 5, 6
(sub nomen Terebratulina triangularis Ether-
idge).
Material. Three articulated specimens, one of them
crushed (NMNHS 31073).
Dimensions (in mm)
Description. Shell small (L
max
, 7.7 mm), triangular to
subtriangular; biconvex with ventral valve more convex.
Shell surface covered with numerous fine ribs; growth
lines also visible. Beak pointed with relatively large, oval
subtriangular, submesothyrid to mesothyrid foramen;
pedicle collar present. Deltidial plates small and dis-
junct. Anterior commissure rectimarginate.
Remarks. Available specimens correspond well to
those illustrated by Owen (1988), and are easily dis-
tinguished from T. imbricata (see above) in having
a subtriangular outline, pointed beak and non-lamellose
growth lines. This is the first record of this species
from Bulgaria, and the first from outside Great
Britain.
Occurrence. Cenomanian of Great Britain; Lower
Cenomanian of northern Bulgaria.
Terebratulina sp.
Fig. 10HeK
Material. Seven articulated specimens, two of them
fragmentary (NMNHS 31073).
Fig. 6. Intraspecific variation in Terebratulina imbricata (Lower Cenomanian, Sanadinovo Formation, northern Bulgaria). Scatter diagrams plotting
length/width (A), length/thickness (B) and width/thickness (C). N, number of specimens.
Specimen # L W T W/L T/L
NMNHS 31073
1 7.7 7.0 2.8 0.91 0.36
2 7.3 5.9 1.9 0.81 0.26
3 3.8 2.5 1.0 0.66 0.26
532 M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Fig. 7. Terebratulina imbricata, Novachene, northern Bulgaria; Sanadinovo Formation (Lower Cenomanian). AeC, ventral, dorsal and lateral views of
juvenile (NMNHS 31072-1); !17. D, E, dorsal and lateral views of NMNHS 31072-2; !10. FeI, NMNHS 31072-3, ventral view, !10 (F), dorsal
view, !10 (G), enlarged posterior portion to show details of foramen, !35 (H), lateral view, !10 (I). JeL, ventral, dorsal and lateral views of NMNHS
31072-4; !10. MeO, ventral, dorsal and lateral views of NMNHS 31072-5; !10. P, dorsal view of NMNHS 31072-6; !10. All SEM micrographs.

Dimensions (in mm) Description. Shell small (L
max
, 9.5 mm), elongate-oval
to subtriangular; biconvex with ventral valve slightly
more convex. Shell surface ornamented by numerous
ribs and growth lines. Beak suberect. Foramen large,
rounded, mesothyrid, bounded by small, triangular and
disjunct deltidial plates. Pedicle collar wide. Lateral
commissure slightly ventrally curved; anterior commis-
sure straight to incipiently uniplicate.
Fig. 8. Terebratulina imbricata, Novachene, northern Bulgaria; Sanadinovo Formation (Lower Cenomanian). A, B, internal view of dorsal valve,
visible are high inner socket ridges and brachidium (NMNHS 31072-7); !14 (A) and !28 (B). C, D, internal views of ventral valves, NMNHS
31072-8 and NMNHS 31072-9, respectively; !20. EeI, NMNHS 31072-10, in dorsal view, !10 (E), enlarged posterior portion of E, !30 (F),
ventral view, !10 (G), enlarged fragment of G to show growth lines of imbricate character, !40 (H), and lateral view, !10 (I). All SEM
micrographs.
Specimen # L W T W/L T/L
NMNHS 31073
4 9.5 e3.2 e0.34
5 7.3 5.9 3.0 0.81 0.41
6 6.9 4.8 2.9 0.70 0.42
7 5.7 4.2 2.8 0.74 0.49
8 4.2 3.1 1.9 0.74 0.45
534 M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Remarks. These specimens differ markedly from
T. imbricata (see above) in outline, ornament and beak
character. They are similar in size and ornament to
T. etheridgei, but differ from that taxon in having an
elongate-oval shape, a wide, short beak and a circular
foramen. These specimens may represent juvenile forms
of T. protostriatula Owen, 1988, a species known from the
Cenomanian of Great Britain (Owen, 1988) and Poland
(Popiel-Barczyk, 1972). However, limited material (i.e.
lacking adult forms) makes specific assignment difficult.
Occurrence. Lower Cenomanian of northern Bulgaria.
Suborder: Terebratellidina Muir-Wood, 1955
Superfamily: Kingenoidea Elliott, 1948
Family: Kingenidae Elliott, 1948
Genus Kingena Davidson, 1852
Type species.Terebratula lima Defrance, 1828,by
original designation of Davidson (1852, p. 42).
Kingena concinna Owen, 1970
Fig. 3KeQ
1852 Kingena lima Defrance; Davidson, p. 42, pl. 5,
figs. 1, 2, 4.
v. 1970 Kingena concinna Owen, p. 57, pl. 5, figs. 6e8;
pl. 6, figs. 4e6.
v. 1972 Kingena concinna Owen; Popiel-Barczyk, p. 124,
pl. 2, figs. 4e6.
Material. Eight articulated specimens, some of them
crushed and decorticated (NMNHS 31074).
Dimensions (in mm)
Description.External morphology. Shell small, oval
to oval-pentagonal in outline, moderately to strongly
biconvex. Maximum width situated at mid-length, while
maximum thickness is in posterior third of shell. Shell
surface smooth, except for fine pustules which, how-
ever, are visible only in some well-preserved fragments
(Fig. 3N). Growth lines better expressed on lateral and
anterior portions of shell. Umbo short, massive, sub-
erect to erect. Dorsal umbo inflated. Foramen small to
medium sized, mesothyrid. Beak ridges short, distinct
Fig. 9. Terebratulina imbricata, Novachene, northern Bulgaria; Sanadinovo Formation (Lower Cenomanian). AeD, transverse sections of brachial
valve (ZPAL Bp.52/6), showing entire shell (A, B) to illustrate acicular primary and fibrous secondary layers; note the difference in thickness of the
primary layer on ribs and between them; C, fragment of the shell showing the boundary between primary and secondary layers; D, section of the
secondary layer showing anvil-shaped fibres. Scale bars represent 100 mm (A, B), 50 mm (C), and 20 mm (D).
Specimen # L W T W/L T/L
NMNHS 31074
1 10.3 8.8 5.8 0.85 0.56
2 10.5 9.2 6.4 0.87 0.61
3 8.9 8.2 5.6 0.92 0.63
535M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

Fig. 10. Early Cenomanian brachiopods from the Sanadinovo Formation, near Novachene, northern Bulgaria. AeG. Modestella geinitzi, ventral,
dorsal and lateral views (AeC) of NMNHS 31075-3; !6.7; DeF, ventral, dorsal and lateral views of NMNHS 31075-1; !6.7; G, enlarged posterior
portion to show details of beak area, same specimen; !20. HeK. Terebratulina sp.; HeJ, ventral, dorsal and lateral views of NMNHS 31073-5; !6.7; K,
dorsal view of NMNHS 31073-6; !8. LeO. Terebratulina etheridgei;LeM, ventral and dorsal views of NMNHS 31073-2, N, dorsal view of NMNHS
31073-1; !6.7. O, enlarged posterior portion to show details of beak area; !15. All SEM micrographs.

in posterior part. Interarea small, partially hidden by
brachial umbo. Deltidial plates disjunct. Lateral com-
missure straight to slightly curved, anterior commissure
rectimarginate.
Internal morphology. Due to the paucity of material,
no serial sections could be prepared and internal
morphology was not studied. In well-preserved speci-
mens the median septum can be traced up to halfway
along the length of the dorsal valve. On exfoliated shells,
the median septum is seen to continue to up to three-
quarters of shell length.
Remarks. Externally, our specimens correspond
closely to the British material (NHM collections,
London) and to a Polish specimen, housed in the
collections of the Museum of the Earth (Warszawa). As
noted previously by Owen (1970) and Popiel-Barczyk
(1972), the distinct ‘‘terebratulid aspect’’ of Kingena
concinna distinguishes it from congeners.
Occurrence. Middle Cenomanian of Great Britain
and France (lower Acanthoceras rhotomagense Zone;
see Gaspard, 1997); Lower Cenomanian of Poland and
northern Bulgaria.
Superfamily: Zeillerioidea Allan, 1940
Family: Zeilleriidae Allan, 1940
Genus Modestella Owen, in Casey, 1961
Type species.Modestella modesta Owen, in Casey, 1961,
by original designation of Owen, in Casey (1961, p. 573).
Modestella geinitzi (Schloenbach, 1866a)
Fig. 10AeG
1866a Magas geinitzi Schloenbach, p. 575.
1866b Magas geinitzi Schloenbach; Schloenbach, p. 32,
pl. 2, figs. 4e8.
1867 Magas geinitzi Schloenbach; Schloenbach,
p. 461.
v. 1972 Modestella sp.; Popiel-Barczyk, p. 134, pl. 3,
figs. 1e3.
v. 1988 Modestella geinitzi (Schloenbach); Owen, p. 154,
pl. 18, figs. 17e22.
1997 Modestella geinitzi (Schloenbach); Gaspard,
p. 154, pl. 1, fig. 14.
Material. Five specimens, two of them broken, one
better preserved, but probably secondarily compressed,
the others decorticated (NMNHS 31075).
Dimensions (in mm)
Description.External morphology. Shell small (L
max
,
6.53 mm), subcircular to subpentagular, biconvex with
ventral valve more convex. Maximum width at about
mid-length. Umbo low, beak pointed, suberect to erect.
Foramen large, circular and hypothyrid. Beak ridges
distinct, sharp. Interarea concave and of medium size.
Hinge line nearly straight. Deltidial plates visually
conjunct in better-preserved specimen and disjunct in
others. Anterior commissure rectimarginate to slightly
unisulcate; lateral commissures straight. One or two
growth lines clearly developed in anterior third of shell.
Internal morphology. Internal structures were not
studied due to scarcity of the material. The median septum
is clearly marked on the externalsurface of the decorticated
brachial valves and extends to halfway the shell length.
Remarks. These small specimens differ from Kingena
concinna with which they co-occur in having a near-
circular outline, a pointed beak, a better-developed
and exposed interarea, well-expressed beak ridges, no
pustules on the shell surface, and in being much less
convex. Although their internal structure remains un-
known, we assign them to M. geinitzi on account of their
close external similarity to material of this genus and
species (see revision by Owen, 1988). The sole difference
between our material and specimens recorded by Owen
(1988) lies in the disjunct deltidial plates of most of the
Bulgarian specimens; this is possibly due to their poor
state of preservation. However, these disjunct deltidial
plates are reminiscent of Polish Modestella sp. described
by Popiel-Barczyk (1972), and considered by Owen
(1988) to be synonymous with Modestella geinitzi.
In his revision of Modestella geinitzi,Owen (1988,
p. 154) noted that ‘‘the species appears to be confined to
localities in Britain and northern France with a marly
limestone facies’’. The occurrence of M. geinitzi in the
Sanadinovo Formation of northern Bulgaria is another
example of preference of this species for marly facies.
Modestella geinitzi is easily distinguished from
M. modesta Owen and M. festiva Owen in being much
smaller and in having a circular outline (Owen, 1963).
Occurrence. Cenomanian of northern Germany,
Great Britain and France (lower Acanthoceras rhotoma-
gense Zone; see Gaspard, 1997); Lower Cenomanian
of Annopol, Poland (Popiel-Barczyk, 1972); Lower
Cenomanian of northern Bulgaria.
5. Conclusions
The Early Cenomanian brachiopod fauna from the
Sanadinovo Formation near Novachene (northern
Bulgaria) comprises members of five families, of which
the Cancellothyrididae constitutes the main group.
Specimens of Terebratulina imbricata dominates the
assemblage studied numerically, accounting for over
Specimen # L W T W/L T/L
NMNHS 31075
1 6.53 6.61 3.83 1.01 0.59
2 ?6.63 6.39 3.00 0.96 ?
3 6.35 6.00 2.90 0.94 0.46
537M.A. Bitner, N. Motchurova-Dekova / Cretaceous Research 26 (2005) 525e539

73%. All taxa, with the exception of Cyclothyris, are here
recorded for the first time from Bulgaria, although all
have been described previously from western and central
Europe. Thus, the present records considerably extend
the geographic range of the species concerned from Great
Britain, northern France and Poland to northern
Bulgaria, which during the Late Cretaceous was along
the southern margin of the North European epicontinen-
tal sea (Jolki
cev, 1984, 1989). This is the most southerly
record of all of the terebratuloid taxa described here. The
Cenomanian transgression, documented from across the
globe, provided relatively stable, shallow-water condi-
tions and low facies diversity (Ager, 1965; Owen, 1988),
which explains why the taxonomic composition of
brachiopod faunas is closely similar. Brachiopods are
facies sensitive and their distribution is controlled by
facies change (Owen, 1978, 1988). Rhynchonelloids are
rare or absent in marly facies, while terebratuloids prefer
marly sediments, of which the present paper provides
another example. Middlemiss (1981) analysed total
species number and the number of newly appearing
species in the AptianeCenomanian interval. The Early
Cenomanian was a period during which numerous
new species originated; among these are such taxa as
Concinnithyris subundata,Terebratulina imbricata,Kingena
concinna and Modestella geinitzi, described herein.
Acknowledgements
We thank Professor N.A. Jolki
cev (Sofia), who
supplied the first brachiopods from the Sanadinovo
Formation, introduced us to them in the field, and
provided data on the geological setting. We also acknowl-
edge the support of EU Sys-Resource grants enabling us to
visit The Natural History Museum, London; Dr. S. Long
is particularly acknowledged for her help in accessing the
brachiopod collections and providing facilities there.
Thanks are due to Dr. E.F. Owen (London) and Dr.
E. Simon (Bruxelles) for helpful discussion, suggestions
and comments on an earlier typescript; Dr. V. Dekov
(Sofia) assisted in the collection and preparation of
material, and all but one macrophotographs were taken
by Ms. G. Dziewin
´ska (Warszawa); the specimen in
Fig. 3H was photographed by the Photographic Unit at
The Natural History Museum, London. A. Holda-
Michalska M.Sc. (Warszawa) assisted in the preparation
of Figs. 1 and 4. SEM micrographs were prepared at the
Institute of Paleobiology (Warszawa) using a Philips XL-
20 scanning microscope. This is a contribution to the joint
Bulgarian-Polish Project 20, ‘‘Cretaceous brachiopods
from Bulgaria and Poland’’, within the framework of
bilateral co-operation between the Bulgarian Academy of
Sciences and the Polish Academy of Sciences. One of us
(NM-D) was in part supported by the Japan Society for
the Promotion of Science.
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