The Late Cretaceous anacoracid shark, Pseudocorax laevis (Leriche), from the Niobrara Chalk of western Kansas

Abstract

Eight isolated teeth of the Late Cretaceous anacoracid shark, Pseudocorax laevis (Leriche), from the Smoky Hill Chalk Member of the Niobrara Chalk in western Kansas are formally identified and described. These teeth were recovered from the bottom half of the Smoky Hill Chalk, which chronostratigraphically ranges from the Late Coniacian (ca. 87 Ma) to the late Early Santonian (ca. 85 Ma). Pseudocorax laevis was likely a small shark, measuring only about 1 m in total length. Like other anacoracids, P. laevis possibly practiced scavenging.

Full text

The Late Cretaceous anacoracid shark, Pseudocorax laevis
(Leriche), from the Niobrara Chalk of western Kansas
Shawn A. Hamm1 and Kenshu Shimada2,3
1. Department of Geosciences, University of Texas at Dallas, P.O. Box 830688, MS
FO21, Richardson, Texas 75083 (sahamm@sbcglobal.net)
2. Environmental Science Program and Department of Biological Sciences, DePaul
University, 2325 North Clifton Avenue, Chicago, Illinois 60614
(kshimada@depaul.edu)
3. Sternberg Museum of Natural History, Fort Hays State University, 3000 Sternberg
Drive, Hays, Kansas 67601
Eight isolated teeth of the Late Cretaceous anacoracid shark, Pseudocorax laevis
(Leriche), from the Smoky Hill Chalk Member of the Niobrara Chalk in western
Kansas are formally identified and described. These teeth were recovered from the
bottom half of the Smoky Hill Chalk, which chronostratigraphically ranges from the
Late Coniacian (ca. 87 Ma) to the late Early Santonian (ca. 85 Ma). Pseudocorax
laevis was likely a small shark, measuring only about 1 m in total length. Like other
anacoracids, P. laevis possibly practiced scavenging.
Keywords: Anacoracidae, elasmobranch, Late Cretaceous, paleoecology, Western
Interior Sea.
TRANSACTIONS OF THE KANSAS
ACADEMY OF SCIENCE
Vol. 110, no. 1/2
p. x1-x15 (2007)
INTRODUCTION
The Smoky Hill Chalk Member of the
Niobrara Chalk Formation is an Upper
Cretaceous rock deposit found primarily in
western Kansas (Hattin, 1982). It was
deposited under an epicontinental sea, the
Western Interior Seaway that crossed North
America in a north-south direction over about
25 million years (Obradovich and Cobban,
1975, p. 50; Kauffman and Caldwell, 1993).
The Smoky Hill Chalk is rich in fossil
vertebrates and, although the fauna is largely
time-averaged (Stewart, 1990; Shimada and
Fielitz, 2006), it includes diverse tetrapods
(e.g., marine turtles, dolichosaurs, mosasaurs,
plesiosaurs, pterosaurs, birds, and non-avian
dinosaurs: (see Everhart, 2005; Shimada and
Bell, 2006) and fishes. Shimada and Fielitz
(2006) recently reviewed the ichthyofaunal
component and found that it contains at least
16 chondrichthyan and 54 osteichthyan taxa.
Pseudocorax laevis (Leriche, 1906) is a Late
Cretaceous anacoracid shark and was one of
the 16 chondrichthyans in the Smoky Hill
Chalk of Kansas listed by Shimada and Fielitz
(2006). However, the record was based on
informal accounts of Hamm (2001) and
Hamm et al. (2002), and Shimada and Fielitz
(2006) noted that occurrences of the species
from the Smoky Hill Chalk were in need of
formal description. The purpose of this
communication is to fulfill this need, and we
also discuss the paleoecology of P. laevis. The
teeth discussed here are housed in Fort Hays
State University, Sternberg Museum of
Natural History (FHSM), Hays, Kansas, and
the University of Kansas, Vertebrate
Paleontology collection (KUVP), Lawrence.
Other institutions referred to in the text are
the Shuler Museum of Paleontology at
Southern Methodist University (SMP-SMU),
Dallas, Texas, and United States National
Museum of Natural History (USNM),
Washington D.C.

SYSTEMATIC PALEONTOLOGY
Class Chondrichthyes
Subclass Elasmobranchii
Order Lamniformes Berg, 1958
Family Anacoracidae Casier, 1947
Genus Pseudocorax Priem, 1897
Pseudocorax laevis (Leriche, 1906)
(Fig. 1)
MATERIAL
FHSM VP-13959, one lateral tooth occurred
between Hattin’s (1982) lithostratigraphic
Marker Unit (MU) 7 and MU 8 in Lane
County (Fig. 1A); FHSM VP-13960, one
lateral tooth occurred between MU 2 and MU
3 in Gove County (Fig. 1B); FHSM VP-
15823, one lateral tooth from 2 m below MU
2 in Trego County (Fig. 1C); FHSM VP-
16523, one anterior tooth from below MU 2
within the Smoky Hill Chalk in Trego County
(Fig. 1D); KUVP 40298, one lateral tooth
from “Niobrara Chalk, western Kansas” (Fig.
1E); KUVP 40299, one lateral tooth from
“Niobrara Chalk, western Kansas” (Fig. 1F);
KUVP 40331, one anterior(?) tooth from
“Niobrara Chalk, western Kansas” (Fig. 1G);
KUVP 84806, one lateral tooth from Rooks
County (Fig. 1H; associated with a series of
mosasaur vertebrae: Fig. 1I). Exact locality
data for each FHSM specimen are on file at
the museum, but those for each KUVP are
uncertain.
STRATIGRAPHY
The exact horizon for each of the four KUVP
specimens is uncertain, but judging from the
general areas in which the museum
prospected fossils when the specimens were
curated, they are all thought to come from the
lower part of the Smoky Hill Chalk. The four
FHSM specimens have better stratigraphic
control and lithostratigraphically range from
‘below MU 2 within the Smoky Hill Chalk’ to
‘between MU 7 and MU 8’ (see above).
x2 Hamm and Shimada
Hattin’s (1982) MU 2 and MU 8 are located
approximately 14.3 m and 80.5 m above the
base of the Smoky Hill Chalk, respectively.
The Smoky Hill Chalk is about 180 m thick
(Hattin, 1982) and, based on the occurrence of
the FHSM specimens, the distribution of
Pseudocorax laevis is currently limited to its
lower half. In terms of Stewart’s (1990)
biostratigraphic zones, this lithostratigraphic
interval spans from the zone of
Protosphyraena perniciosa (Cope) to the zone
of Cladoceramus undulatoplicatus (Roemer)
(see Everhart, 2005, table 2.1), and ranges
from the Late Coniacian (ca. 87 Ma) to the
late Early Santonian (ca. 85 Ma) (Hattin,
1982; Kauffman et al., 1993).
DESCRIPTION
FHSM VP-13959, VP-13960, and VP-15823
as well as KUVP 40298, 40299, and 84806
(Fig. 1A–C, E, F, H) are nearly identical in
size and morphology. They measure about 5–6
mm in both total height and total width, and
have the maximum vertical crown
(enameloid) height of about 4–4.5 mm and
the maximum crown width of about 4.5–5.5
mm. They have a distally inclined (at about
45° angle), labiolingually thin, triangular
cusp with a gently convex distal heel
separated by a notch, and an asymmetrical
bilobed root. Both the cusp and distal heel
have smooth lingual and labial surfaces and
bear well-defined, unserrated cutting edges
(note: FHSM VP-15823 has a jagged mesial
cutting edge due to damage). The upper half
of the mesial cutting edge of the cusp is gently
convex, whereas the lower half shows a slight
concavity. The distal cutting edge of the cusp
is straight. A narrow neck is present between
the crown and root on the lingual side,
whereas the crown base on the labial side is
gently concave and forms a well-developed
ledge that overhangs the root. The root
possesses a low lingual protuberance with a
deep nutritive groove that bisects the two
lobes. The mesial lobe is narrower than the

Transactions of the Kansas Academy of Science 110(1/2), 2007 x3
Figure 1. Teeth of Pseudocorax laevis (Leriche) from the Smoky Hill Chalk of western Kansas.
A, FHSM VP-13959, lateral tooth; B, FHSM VP-13960, lateral tooth; C, FHSM VP-15823, lateral
tooth; D, FHSM VP-16523, anterior tooth; E, KUVP 40298, lateral tooth; F, KUVP 40299, lateral
tooth; G, KUVP 40331, anterior(?) tooth; H, KUVP 84806, lateral tooth; I, KUVP 84806 (see Fig.
1H) found on a series of platecarpine mosasaur vertebrae [Platecarpus ictericus (Cope): oblique
lateroventral view; anterior to the right]. Orientation: A–D, left = lingual view, right = labial view;
E–H, lingual view. Scale: A–H = 2 mm; I = 2 cm.

x4 Hamm and Shimada
distal root lobe. It is pointed mesiobasally,
whereas the distal lobe is directed distally.
The basal concavity of the root is shallow.
FHSM VP-16523 (Fig. 1D) differs
significantly from the aforementioned six
teeth in having a robust, symmetrical crown
and root. It measures 7 mm and almost 6 mm
in total tooth height and crown height,
respectively. One of the root lobes along with
a small portion of the crown base is damaged,
but the estimated tooth width and crown
width are 4 mm and 4.5 mm, respectively.
The erect crown is triangular, smooth
surfaced, and unserrated, and it widens
laterally on its bottom one-third by forming
an exceptionally low heel on both mesial and
distal sides. The base of the crown on the
labial side forms a concave ledge. The root
has basally extended lobes, a deep nutritive
groove, and a moderately tight basal
concavity.
KUVP 40331 (Fig. 1G) is the smallest tooth
in our sample. It measures about 4.5 mm in
total tooth height, 3.5 mm in total tooth
width, 4 mm in crown height, and 3 mm in
crown width. Morphologically, it is
intermediate between FHSM VP-16523 and
the other six teeth. It is equipped with a tall,
slightly inclined crown and a weakly
differentiated distal heel.
Taxonomic Remarks
Teeth of the genus Pseudocorax are found in
Upper Cretaceous marine deposits of North
America, Europe, Middle East (Israel),
Africa, and Asia (e.g., Cappetta, 1987; Lewy
and Cappetta, 1989; Kitamura, 1997;
Kitamura et al. 1995; see below for additional
references). In addition to P. laevis, three
other Pseudocorax species are known: 1) P.
affinis (Agassiz, 1843); 2) P. granti Cappetta
and Case, 1975; and 3) P. primulus Müller
and Diedrich, 1991. It should be noted that
Corax australis, from the Albian of Australia
(Chapman, 1908), was referred to
Squalicorax australis by Cappetta (1987, p.
109), and later to P. australis by Kemp (1991).
However, the species has subsequently been
reassigned to Echinorhinus (Kemp, 1996).
Pseudocorax primulus is known only from the
Cenomanian of Germany and has been
distinguished from all other Pseudocorax
species (including P. laevis) by smooth cutting
edges and the lack of a nutrient groove
(Müller and Diedrich, 1991). Our opinion of
the P. primulus material described by Müller
and Diedrich (1991) is that the teeth are more
like those of another anacoracid shark,
Squalicorax, especially S. volgensis.
Pseudocorax affinis is the only species within
the genus that possesses serrated cutting edges
(Leriche, 1906). The taxon has been reported
from the Campanian of Germany (Ladwig,
2000), and the Maastrichtian of Holland
(Geyn, 1937), Belgium (Albers and Weiler,
1964), Morocco (Arambourg, 1952; see
Cappetta, 1987; Antunes and Cappetta, 2002),
and possibly from Upper Campanian–
Maastrichtian deposits in Israel (as
“Pseudocorax aff. affinis” by Lewy and
Cappetta, 1989).
Although Pseudocorax granti is
morphologically similar to P. laevis, P. laevis
was separated from P. granti by having
smaller teeth with more slender crowns
(Cappetta and Case, 1975; Case and Cappetta,
1997). Both morphologies have a similar
geographic distribution (see below). We refer
our Niobrara specimens to P. laevis because,
as in the type specimen described by Leriche
(1906), each tooth possesses a labiolingually
compressed crown, smooth cutting edges, a
strong labial basal crown ledge, and strongly
bilobate root with a deep nutrient groove.
Examination of several thousand Pseudocorax
teeth from Texas (S.A.H., unpublished data)
indicates that the criteria used to separate P.
granti from P. laevis are weakly founded, and
our contention is that the taxa can be regarded
as conspecific, with P. laevis having priority.
In addition to the Smoky Hill Chalk, P. laevis

Transactions of the Kansas Academy of Science 110(1/2), 2007 x5
has been reported from Turonian and
Campanian deposits of France (Leriche,
1906), Coniacian to Maastrichtian strata of
Texas (as “P. granti” in Cappetta and Case,
1975, 1999; Case and Cappetta, 1997; Welton
and Farish, 1993), as well as the Campanian
of Belgium (Herman, 1977; Cappetta, 1987),
England (Woodward, 1911), Alabama (“P.
affinis” of Applegate, 1970; Cappetta, 1987;
Kiernan, 2002), Delaware (“P. granti” of
Lauginiger and Hartstein, 1983), Georgia (“P.
affinis” of Case and Schwimmer, 1988), and
Mississippi (“P. granti” of Case, 1991).
Shimada (1997, p. 929) reported a tooth set of
“cf. Pseudocorax sp.” from the Smoky Hill
Chalk that occurred in close proximity with
skeletal remains of another shark,
Cretoxyrhina mantelli (Agassiz) (catalogued
as KUVP 55060). However, a re-examination
of the tooth set revealed that it belongs to a
species of Squalicorax (K.S., unpublished
data). As a noteworthy side note,
Pseudocorax is unique among other
lamniform sharks in that its teeth possess
crown margins thin enough to transmit light
(see also Leriche, 1906).
Anatomical Remarks
The dental pattern of Pseudocorax is
unknown because the taxon is only
represented by isolated teeth. However, the
cusp inclination in previously reported
Pseudocorax teeth is relatively wide ranging,
from nearly vertical at about 75°, to highly
inclined at over 40° (see Welton and Farish,
1993, p. 123). This observation indicates that
the taxon had a heterodont dentition, although
whether or not Pseudocorax had a ‘lamnoid
tooth pattern’ (sensu Compagno, 1984;
Shimada, 2002) is uncertain (note that the
lamnoid dental pattern was not found in
another anacoracid shark, Squalicorax
Whitley by Shimada and Cicimurri, 2005).
Nevertheless, it is reasonable to assert that if
Pseudocorax is indeed a lamniform shark, the
dentition in each jaw quadrant consisted of
two rows of erect ‘anterior teeth,’ followed by
multiple rows of inclined ‘lateral teeth’ (sensu
Shimada, 2002). Among the eight P. laevis
teeth described here, the cusp inclinations are
relatively high in FHSM VP-13959, VP-
13960, and VP-15823, as well as in KUVP
40298, 40299, and 84806 (ca. 45°: Fig. 1A–
C, E, F, H), suggesting that they represent
lateral teeth. FHSM VP-16523 (Fig. 1D) is
considered an anterior tooth because it has a
nearly vertical cusp, whereas the slight cusp
inclination in KUVP 40331 (Fig. 1G)
suggests that the tooth represents either a
distally located anterior tooth, or a mesially
located lateral tooth.
Among the six lateral teeth, FHSM VP-13959
(Fig. 1A) has the most inclined cusp, the
broadest root, and the shallowest basal root
concavity, suggesting that it is the distalmost
lateral tooth in our sample. Additionally, it
should be noted that the cusp inclinations
suggest that FHSM VP-13959 and VP-13960
(Fig. 1A, B), KUVP 40298 and 40299 (Fig.
1A, B, E, F), were from either the upper right
or lower left dentition. FHSM VP-15823,
KUVP 40331, and KUVP 84806 (Fig. 1C, G,
H) were from either the upper left or lower
right dentition, but FHSM VP-16523 (Fig.
1D) is too symmetrical to decisively determine
which jaw quadrant the tooth was located in
life.
DISCUSSION
As probable top predators, inferences about
the body size of extinct sharks are important
for deciphering the paleoecology of ancient
marine ecosystems. However, the body size
estimation for Pseudocorax laevis is
particularly difficult because the taxon is
known only from isolated teeth. To make the
matter more difficult, Shimada and Cicimurri
(2005) found that the exact quantitative
relationship between the total length and
tooth size in another anacoracid, Squalicorax,
is species-specific (based on some partial and
complete skeletons). Nevertheless, the most
complete Squalicorax skeleton, USNM
425665 (S. falcatus), which measures 2 m in

x6 Hamm and Shimada
total body length has teeth with a maximum
crown height of 11 mm. Given that the crown
height of P. laevis (ca. 4–6 mm) is only about
half of that size, it is likely that P. laevis was
a small shark measuring only about 1 m in
total length.
The four FHSM specimens of Pseudocorax
laevis from the Smoky Hill Chalk (Fig. 1A–
D) occurred in two biostratigraphic zones of
Stewart (1990): the zone of Protosphyraena
perniciosa (Cope) and zone of Cladoceramus
undulatoplicatus (Roemer) (see above). The
occurrences of the four KUVP specimens
described here (Fig. 1E–H) are also likely
within one of these two zones. Stewart (1990)
listed six invertebrate, at least 28 fish, and six
tetrapod taxa in the former zone, and six
invertebrate, 15 fish, and two tetrapod taxa in
the latter zone. Teeth of P. laevis have also
been reported from the zone of ‘Spinaptychus
n. sp.’, another biostratigraphical interval
partially within the zones of P. perniciosa and
C. undulatoplicatus, but Stewart (1990, p. 29)
did not refer to any specific specimens.
A tylosaurine mosasaur skeleton (SMU-SMP
75586) recovered from the Ozan Formation
(Late Campanian) of Fannin County, Texas,
was associated with a tooth of P. laevis (SMU-
SMP 76332) and three teeth of S. pristodontus
(Agassiz) (SMU-SMP 75587: Fig. 2). This
tylosaur specimen exhibits extensive shark
bite marks on its cranial elements, ribs, and
vertebrae (Fig. 2B). Whereas some bite marks
exhibit serration grooves indicating that they
were made by S. pristodontus, other small
scratch-like bite marks without serration
grooves may be attributable to P. laevis.
Although no bite marks were found on the
bones, teeth of S. falcatus and P. laevis were
found in direct association with a partial
skeleton of Platecarpus ictericus (Cope)
(KUVP 84803: Fig. 1I) collected from the
Smoky Hill Chalk in western Kansas. These
mosasaur remains are important because they
Figure 2. Pseudocorax laevis (Leriche) associated with tylosaurine mosasaur from Ozan
Formation (Late Campanian) in Fannin County, Texas. A, tooth of P. laevis (SMU-SMP 76332:
top = lingual view; bottom = labial view; scale = 2 mm); B, three selected rib fragments of
tylosaurine mosasaur (SMU-SMP 75586: scale = 2 cm), showing bite marks putatively made
by P. laevis and/or Squalicorax pristodontus (Agassiz).

Transactions of the Kansas Academy of Science 110(1/2), 2007 x7
represent the only known occurrences in
which P. laevis is directly associated with a
skeleton of another fossil vertebrate. We
interpret these associations as evidence that P.
laevis was an opportunistic feeder.
ACKNOWLEDGEMENTS
The collectors of Pseudocorax specimens
described here include B. Dunn, K. Ewell,
J.D. Stewart, and E. Swiatovy. We thank R.J.
Zakrzewski, M.J. Everhart (FHSM) and M.J.
Polcyn (SMU-SMP) for allowing access to the
specimens. M. Siverson (Western Australian
Museum) contributed insightful information
on Pseudocorax. The comments and
suggestions of D.J. Cicimurri (Clemson
University) and an anonymous reviewer are
greatly appreciated and vastly improved an
earlier version of this manuscript.
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