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Paludicola 4(4):125-136 June 2004
by the Rochester Institute of Vertebrate Paleontology
An associated dentition and calcified vertebral centra of the
Late Cretaceous elasmobranch, Ptychodus anonymus Williston 1900
Michael J. Everhart
1
and Tom Caggiano
2
1-Sternberg Museum of Natural History, Hays, KS 67601. 2-145 Hayrick Lane, Commack, NY 11725
ABSTRACT
The associated remains of a ptychodontid shark, Ptychodus anonymus Williston 1900, were recovered by the authors from
the Smoky Hill Chalk Member (Late Cretaceous; late Coniacian) of the Niobrara Chalk Formation of western Kansas.
Preserved elements included 208 teeth, five vertebral centra, fragments of centra and calcified cartilage, and oral (pharyngeal)
denticles. The presence of calcified vertebral centra indicate that Ptychodus is a neoselachian shark and not a hybodont as
previously reported. Whereas individual teeth of the genus Ptychodus are relatively common fossils in Late Cretaceous marine
sediments, reasonably complete dentitions and preserved soft tissues are rare, and few have been reported in the literature. Most
of the Ptychodus teeth that have been documented previously from the Niobrara Chalk have not included accurate stratigraphic
information. In addition to reporting the associated dentition, calcified vertebral centra and oral denticles of Ptychodus
anonymus, we also review the fauna association of the specimen and the history of the genus in North America.
INTRODUCTION
Ptychodus is a genus of extinct durophagous
sharks whose remains are found in Late Cretaceous
marine sediments around the world. The unusual teeth
of ptychodontid sharks were first described by Agassiz
(1833-1844) from the English chalk. Leidy (1868) was
the first to report on the discovery of Ptychodus teeth
from the "Cretaceous series" of western Kansas when
he described a single, damaged tooth (Ptychodus
occidentalis) from "a few miles east of Fort Hays,
Kansas." At about the same time, Dr. George M.
Sternberg collected Ptychodus mortoni teeth from the
Niobrara Chalk of western Kansas, which were later
figured by Leidy (1873). Cope (1874, p. 47-48; 1875,
p. 294) listed five species of Ptychodus from different
stratigraphic horizons in Kansas: P. janewayi, P.
polygyrus, P. occidentalis, P. mortoni and P. whipplei.
However, while most of Cope’s specimens are
assumed to be curated in the American Museum of
Natural History, his name is not associated with any
Ptychodus material currently in the AMNH collection.
Another early collector in Kansas, B. F. Mudge (1876,
p. 217) noted that the “teeth of Selachians are quite
common. At one locality, over 400 were collected in an
area of 30 inches, and apparently from the jaws of one
individual – a Ptychodus – and all in excellent
preservation.” Mudge’s specimens were most likely
maintained in the museum of the Kansas Academy of
Science but, according to Skelton (1996), the entire
KAS collection was moved and dispersed about 1915,
and the museum was never reconstituted.
Unfortunately, except for the small P. occidentalis
tooth described by Leidy (1868), there is no further
record of the fate of these early Kansas specimens.
Williston (1900, Pl. 29, fig. 5-8, 16-18, 20-22, 24)
described two new species of Ptychodus (P. martini
and P. anonymus) from the Smoky Hill Chalk and
published the first photographs of the teeth of seven
species (Ptychodus mortoni, P. martini, P. occidentalis,
P. anonymus, P. polygyrus, P. whipplei and P.
janewayi) from western Kansas. The discovery of a
well-preserved specimen of P. mortoni, including
calcified centra, was reported by Stewart (1980) but the
specimen has not been further described. Stewart
(1990) reported only three species (P. mortoni, P.
martini and P. anonymus) from the Smoky Hill Chalk
and proposed the first stratigraphic distribution of
ptychodontids in that member, suggesting that they are
limited stratigraphically to the lower third of the
member (late Coniacian – early Santonian). Although
many additional specimens of this genus have been
recovered in Kansas during the last one hundred years,
little information has been added to the literature since
Williston (1900).
This paper describes the fragmentary remains of a
Ptychodus anonymus specimen (AMNH 19553)
collected by the authors from western Kansas in 1995,
and donated to the American Museum of Natural
History (AMNH).
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PALUDICOLA, VOL. 4, NO. 4, 2004
126
Locality and Stratigraphy--AMNH 19
553 was
discovered in the Smoky Hill Chalk Member of the
Niobrara Formation in southeastern Gove County,
Kansas, about five miles south of Castle Rock. The
exact locality is on record at the American Museum of
Natural History. The remains were located about 3 m
above the uppermost bed of bioturbulated chalk in
Hattin's (1982) Marker Unit 3, and 32 m above the
contact with the underlying Fort Hays Limestone
(Figure 1). The top of the Fort Hays Limestone is
exposed along the Smoky Hill River less than two
miles to the southeast. The specimen occurred near the
upper limits of Stewart's (1990) biostratigraphic zone
of Protosphyraena perniciosa, just below the base of
the zone of Spinaptychus n. sp. and would be late
Coniacian in age.
Faunal Association--The
inoceramids, Volvice-
ramus grandis and Pl
atyceramus platinus, and the
ostreid, Pseudoperna congesta, are the most common
macroinvertebrates in this zone. Fragments of the
rudist, Durania maxima, are found occasionally, as are
pen fragments of the squid, Tusoteuthis longa. The
remains of vertebrates collected by the authors from
this locality include: (Elasmobranchs) Cretoxyrhina
mantelli, Cretolamna appendiculata, Squalicorax
falcatus, Ptychodus mortoni, P. anonymus, P. martini,
P. polygyrus; (Teleosts) Protosphyraena perniciosa, P.
nitida, Xiphactinus audax, Ichthyodectes ctenodon,
Gillicus arcuatus, Saurodon leanus, Pachyrhizodus
caninus, P. minimus, Cimolichthys nepaholica,
Enchodus petrosus, E. gladiolus, Martinichthys brevis,
and Thryptodus zittelli; (Reptilia) Tylosaurus
nepaeolicus and other unidentified mosasaur remains.
Associated teeth of Ptychodu
s martini
(Hamm
and Everhart, 1999) and the lamniform shark,
Scapanorhynchus raphiodon (Hamm and Shimada,
2002) were also recently documented from the same
exposure. Nicholls (1988) reported a nearly complete
specimen of the marine turtle, Toxochelys latiremis,
from a site further east in the same section. The
fragmentary skull of a polycotylid plesiosaur was
reported by Everhart (2003) from the same
stratigraphic interval approximately 4 miles to the
southwest. A more comprehensive listing of vertebrate
species was provided by Stewart (1990) from this and
other biostratigraphic zones in the Smoky Hill Chalk.
MATERIALS AND METHODS
AMNH 19553 consists of portions of the upper
an
d lower dentitio
ns of a ptychodontid shark totaling
201 teeth, five nearly complete vertebral centra (54 mm
diameter), several centra fragments, calcified cartilage,
oral denticles, and two associated teeth of the
anacoracid shark, Squalicorax falcatus.
AMNH 19553 was discovered in April, 1995, by
one
of
us (TC) while on a field trip in southeastern
Gove County, Kansas. Numerous teeth were located as
float in a small gully at the edge of a shallow valley in
the Smoky Hill River drainage. The loose teeth were
followed up slope to where additional remains were
eroding from the chalk. Unfortunately, only a few teeth
remained in situ. The matrix surrounding those teeth,
however, yielded five articulated vertebral centra,
several fragments of centra, and some debris that
appeared to be composed of calcified cartilage. A
quantity of the surrounding matrix was collected and
the area was searched for any additional remains.
A portion of the matrix recovered from around the
speci
men was pr
ocessed with dilute acetic acid by J. D.
Stewart (Los Angeles County Museum of Natural
History –LACMNH). More than 150 oral (pharyngeal)
denticles were recovered from this matrix sample along
with several teeth of Cimolichthys nepaholica and
Enchodus sp., and scales of Paraliodesmus gaudagnii
(Stewart, pers. comm., 1995). Seven of the 208 teeth
recovered from the specimen are curated as LACMNH
138527 to provide providence for the oral denticles
collected by Stewart.
The AMNH specimen includes fourteen large,
symm
etrical
medial teeth that range in size from 19
mm by 18 mm mesial–distally to 25 mm by 23 mm
labial-lingually. The labial margins of these tooth
crowns are convex and the lingual margins are concave
(Figure 2). The labial edge of each crown sits on a
shelf formed in the lingual margin of the preceding
crown (Figure 3). AMNH 19553 preserves a single
tooth from the symphysial tooth row in the upper jaw
that measures 9 mm mesial–distally and 8 mm labial-
lingually (Figure 4). The root of this tooth is overhung
by the crown shelf at the labial edge and compares well
with the upper jaw medial tooth figured by Woodward
(1887, Pl. 10, fig. 11). The remaining teeth in the
specimen are asymmetrical. The larger lateral teeth,
positioned adjacent to the medials, range in size from
20 mm by 14 mm to 24 mm by 20 mm. Intermediate
lateral teeth range from 18 mm by 14 mm to 14 mm by
9 mm. Posterior teeth (defined as those teeth at the
distal edges of each jaw plate) range from 13 mm by 11
mm to 12 m by 8 mm. Crown height is greatly
diminished in the most distal teeth. In occlusal view,
the crown morphology changes dramatically
mesodistally and the cusp becomes more offset
distally.
The roots are not centered und
er the cr
owns of the
teeth in this specimen. On medial teeth, the crown shelf
is centered in a mesial-distal direction. The root is
almost flush with the lingual edge of the crown shelf,
while the crown shelf overhangs the root at the labial
edge. The roots tend to be flush at the mesial and
lingual sides of the asymmetrical teeth that make up the
Paludicola 4(4):125-136 June 2004
by the Rochester Institute of Vertebrate Paleontology
FIGURE 1. A generalized stratigraphic column of Late Cretaceous rocks in Kansas showing the temporal range of the genus Ptychodus, and the
approximate stratigraphic occurrence of AMNH 19553. (Adapted from Shimada, 1996)
127
PALUDICOLA, VOL. 4, NO. 4, 2004
128
FIGURE 2. An occlusal view of a medial tooth from the lower jaw of Ptychodus anonymus (AMNH 19553). Labial is to the top of the photograph.
Note the ornamentation in the marginal area surrounding the crown and the shelf formed on the posterior side of the crown. (Scale = mm)
FIGURE 3. An occlusal view of two medial teeth from the lower jaw of AMNH 19553 showing the articulation of the protuberance on the labial
edge of the following tooth with the shelf formed in the lingual notch of the leading tooth in the row. Anterior is to the left. (Scale = mm)
Paludicola 4(4):125-136 June 2004
by the Rochester Institute of Vertebrate Paleontology
lateral and posterior sections of the jaw plate, and the
crown shelf overhangs on the labial and distal sides.
The roots contain numerous foramina just below the
crown – root contact.
Approximately 10% of the teeth in this specimen
show visible wear facets on the apex of the crown.
None exhibit the extreme wear in evidence on some
ptychodontid teeth (Authors pers. observations).
Twelve of the teeth are incompletely formed
replacement teeth (Figure 5). Most of these are hollow
crowns with the enamel in various stages of
completion. Several, however, are more developed and
are partially filled with the dentine that would
eventually have formed the bilobate root. These crowns
would have been located in the most lingual (posterior)
positions in the tooth rows. Similar replacement teeth
have been observed by the authors in other associated
Ptychodus tooth sets (FHSM VP-2222, VP-2223 and
VP-14854). Traces of wear were first reported and
figured by Woodard (1887, p. 126-127; Pl. 10, fig. 13).
Five circular centra were recovered in partial
articulation (Figure 6) from the site along with
numerous fragments. The centra were extremely fragile
and were not prepared prior to donation. All of the
centra are fractured and none are 100 percent complete.
The centra measure 54 mm in diameter and are 4 mm
thick. Concentric layers of calcified cartilage are
visible on the edges of fractures. The surface of each
centrum exhibits fine grooves which radiate outward
from the center. Foramina are not apparent, and
openings for the basidorsal / basiventral cartilages were
not observed. Stewart (1980) reported slightly larger
(63-63 mm), compressed centra in association with a
Ptychodus mortoni specimen (KUVP 59041) in the
collection of the University of Kansas. An examination
of the KUVP 59041 remains in 2004 by one of us
(MJE) located only three partial vertebrae (Figure 7).
These fragments are similar in structure and surface
detail to the centra from the AMNH specimen. The
calcified centra from both specimens conform closely
to the asterospondylic type figured by Cappetta (1987,
fig. 9C). Although Cappetta (Ibid.) and others have
suggested that Ptychodus is a hybodont on the basis of
the similarities in the dentitions, the presence of
calcified centra indicates that it is instead a
neoselachian, as are all modern sharks and rays.
Additional work is required on more complete
specimens, such as KUVP 59041, to further define the
systematic relationships.
Cappetta (1987, p. 21) noted that “the inside of
the mouth is also covered, in many selachians, by
numerous mucous membrane denticles,” but did not
provide a description. Oral (pharyngeal), denticles
were collected from the matrix around AMNH 19553
by Stewart (pers. comm., 1995), and in addition, a
small number were recovered by the authors from the
matrix adhering to inside of the hollow tooth crowns of
some of the partially formed replacement teeth. The
hollow underside of these replacement teeth apparently
served as traps for denticles as the specimen decayed.
The denticles measure just over 1 mm in length and 0.5
mm in maximum width across the cusp (Figure 8), and
appear to be composed of an enamel-like material. The
cusps are inflated and exhibit from one to three lobes.
The smooth upper surface of the cusp contrasts
markedly with the highly ornamented dermal denticles
of various shark species (Cappetta, 1987, fig. 31). The
opposite end tapers to a point and would appear to be
the portion that anchored the denticle into the epithelial
lining of the mouth. We were also able to collect
similar oral denticles from the replacement teeth of a
second P. anonymus specimen (FHSM VP-14854)
recovered near the same locality as AMNH 19553 in
1999 (Everhart, et al., 2003).
Two teeth of the shark Squalicorax falcatus were
discovered in close association with the AMNH 19553
specimen, suggesting possible scavenging of the
Ptychodus remains. Squalicorax is well documented as
a scavenger of vertebrate remains in the Late
Cretaceous Western Interior Sea and Gulf Coast areas
(Schwimmer, et al., 1997). While no direct evidence of
scavenging was apparent on the AMNH 19553
specimen, it is unusual to otherwise find the remains of
two vertebrate species in such close association in the
Smoky Hill Chalk. It is uncertain if the teleost remains
recovered from the matrix by Stewart (pers. comm.,
1995) are associated with the specimen or are simply a
part of the normal detritus which had accumulated on
the sea floor.
SYSTEMATIC PALEONTOLOGY
Class Chondrichthyes Huxley, 1880
Subclass Elasmobranchii Bonaparte, 1838
Cohort Euselachii Hay, 1902
Subcohort Neoselachii Compagno 1977
Order incertae sedis
Family Ptychodontidae Jaekel, 1898
Genus Ptychodus Agassiz, 1835
Ptychodus anonymus Williston 1900
Discussion--Woodard (1887, p. 128) noted that
the dentition of Ptychodus “is that of a true Ray, and
does not bear the slightest resemblance to that of the
Cestraciont Sharks.” While the Family Ptychodontidae
has more recently been included in the Superfamily
Hybodontoidea Zangerl, 1981 (Cappetta, 1987; Welton
and Farish, 1993, and others), Stewart (1980)
suggested that “…that all living sharks and rays
(including Heterodontus) are members of the
monophyletic Neoselachii, united by synapomorphies
including the presence of calcified centra. Since
129
Paludicola 4(4):125-136 June 2004
by the Rochester Institute of Vertebrate Paleontology
FIGURE 4. A) Labial views of a medial tooth from the upper jaw (upper left), and B) a medial tooth from the lower jaw. (Scale = mm)
FIGURE 5: Oblique views of two of the replacement tooth crowns recovered in association with AMNH 19553. These crowns demonstrate that the
enamel of the tooth is completed prior to the formation of the bilobate root. (Scale = mm)
130
EVERHART AND CAGGIANO--CRETACEOUS ELASMOBRANCH, PTYCHODUS ANONYMUS
131
FIGURE 6: Two of the five calcified vertebral centra collected in association with AMNH 19553. The presence of calcified centra places Ptychodus
in the Neoselachii with modern sharks and rays. The diameter of each vertebra is approximately 54 mm.
FIGURE 7: Three fragmentary vertebrae from the Ptychodus mortoni specimen (KUVP 59041) reported by Stewart (1980). (Scale = cm)
PALUDICOLA, VOL. 4, NO. 4, 2004
132
Ptychodus shares this derived state, it must be regarded
as a neoselachian and not as a hybodont …”
Stewart’s
conclusion was based on calcified centra found in a
relatively complete specimen Ptychodus mortoni which
is now in the University of Kansas collection (KUVP
59041). Cappetta (1987, p. 37) acknowledged
Stewart’s comments, but noted that “it cannot be
excluded that calcified centra appeared parallely in
very specialized hybodonts like Ptychodus.”
Unfortunately, KUVP 59041 has not been described
further. Stewart’s (1980) suggestion is followed here
while the authors note that additional refinement is
necessary regarding the placement of the Family
Ptychodontidae within the Neoselachii.
Ptych
odontids are recognized most readily by
thei
r rounded, sub-rectangular teeth that are arranged in
parallel, interlocking rows to form a pavement on the
upper and lower jaws. According to Kauffman (1972),
this feeding mechanism apparently evolved in response
to a durophagous diet. Most workers divide Ptychodus
teeth into morphological types based on crown
development: low, intermediate and high (Welton and
Farish 1993). P. anonymus falls into the high crowned
type. All species exhibit transverse enameloid ridges,
except for P. mortoni whose ridges radiate in all
directions from the center of the cusp. Ptychodontid
teeth also exhibit distinctive ornamentation on the
marginal areas around the crown (Figure 2). The crown
shape, transverse ridges and marginal ornamentation
are the diagnostic features used to distinguish among
the various species. In all species, the enameloid crown
extends over the low, weakly bilobate root.
As clarification, consistent with Wooda
rd (1887)
and Dibley (1911), the term row indicates a labio-
lingual column of teeth. The lower dentition has a
medial row that contains the largest teeth in the
dentition (Woodward, 1887, 129; Dibley, 1911, p.
263), while the opposing medial row of the upper
dentition contains relatively small medial (symphysial)
teeth flanked by rows of larger teeth that collectively
form a furrow for the medial row of large lower teeth
to fit into. The small medial row teeth in the upper jaw
are symmetrical (Figure 3A) as are the teeth in medial
row in the lower jaw. The ptychodontid dentition
displays monognathic heterodonty in that the tooth
shape changes from mesial to distal along the dental
series. The teeth become more asymmetrical toward
the lateral rows. This condition has also been reported
in P. whipplei (Welton and Farish, 1993) and P.
occidentalis (Cicimurri (2001).
Teeth of the genus Ptych
odus are
known from
Late Cretaceous marine sediments of every continent
except Australia (Cappetta, 1987, p. 38). In North
America, the genus has been reported from numerous
localities within the extent of the Western Interior Sea.
The largest number of ptychodontid species has been
reported from Texas (Welton and Farrish, 1993) but
they are also well known from Kansas (Leidy, 1868,
1873; Cope, 1874, 1875; Mudge, 1876; Williston,
1900; Stewart, 1980, 1990; Shimada, 1993; Shimada
and Martin, 1993; Everhart, et al., 2003; Shimada and
Everhart, 2003), Alabama (Morton, 1842; Applegate,
1970), Georgia (Case and Schwimmer, 1988),
Mississippi (Manning and Dockery, 1992), South
Dakota (Cappetta, 1973), Arizona (Williamson, et al.,
1993), New Mexico (Williamson, et al., 1990), Utah
(this paper), Wyoming (Evetts, 1979; Cicimurri, 2004)
and Canada (Case, et al., 1990). Stewart (1988)
reported the first North American occurrence from
California.
P. anonymus
has a more restricted ge
ographic
range and is apparently limited to the Western Interior
Sea of North America. The type locality was originally
described by Williston (1900, p. 241) as being from
"Walnut Creek" and "probably" from the "Benton" of
Kansas. Hattin (1982) noted that the Benton Formation
is an obsolete term that originally included the
Graneros Shale, Greenhorn Limestone and Carlile
Shale, and thus is middle Cenomanian through middle
Turonian in age. Exposures of rocks of this age in
Kansas are generally restricted to the north-central part
of the state. The only "Walnut Creeks" in north-central
Kansas are in Norton, Phillips and Jewell counties. The
Smoky Hill Chalk Member crops out occasionally in
Norton and Phillips counties but there are no
documented exposures of the "Benton" there. In Jewell
County, there is a Walnut Creek near the town of Burr
Oak, west of Mankato, KS. Exposures in the area
include the basal Fort Hays Limestone and the Carlile
Shale. This area is most likely close to the locality of
Williston's type specimen of P. anonymus. If so, the
material would be middle Turonian to early Coniacian
in age.
Whereas the genus Pt
ychodus
has a temporal
range from the Albian into the early Campanian
(MacLeod and Slaughter, 1980), P. anonymus has been
documented only from the middle Cenomanian through
the late Coniacian. Meyer (1974) and Welton and
Farish (1993) indicate that P. anonymus occurs
commonly in the Cenomanian and Turonian of Texas.
Lucas, et al. (1988) and Wolberg (1985) documented
the species from the latest Cenomanian and the
Turonian of New Mexico respectively. It is also known
from the late Cenomanian-middle Turonian Tropic
Shale of Utah as well (M. Graffam, pers. comm., 1999;
J. Bourdon, pers. comm., 1999). Parkin, et al. (2002)
reported P. anonymus from the Greenhorn Limestone
(middle Cenomanian) of Colorado. Cicimurri (2001,
2004) documented the species from the late
Cenomanian – Turonian of South Dakota. In his
discussion of Niobrara Formation vertebrate
stratigraphy, Stewart (1990) noted that P. anonymus
Paludicola 4(4):125-136 June 2004
by the Rochester Institute of Vertebrate Paleontology
FIGURE 8: (Left to right) Occlusal, lateral and basal views of an oral (pharyngeal) denticle recovered from the remains of AMNH 19553. These
denticles formed a protective lining in the throat of the shark. (Scale = mm)
________________________________________________________________________
and Graneros Shale (middle Cenomanian) of Russell
County (Everhart, 2004, pers. observation).
was known from the Greenhorn and Carlile formations
of Kansas, and stated that the range of the taxon
extended upward into the biostratigraphic zones of
Protosphyraena perniciosa and Spinaptychus n. sp. in
the lower Smoky Hill Chalk. These zones include the
stratigraphic Marker Units 1-5 of Hattin (1982) and
encompass late Coniacian through early Santonian
time. AMNH 19553 would represent a relatively late
occurrence of the species.
Williston (1900) described the teeth of Ptychodus
anonymus as having "broadly conical crowns" and
"very distinctly reticulate marginal areas", with
"transverse ridges not reaching the rims of the crowns."
Although Williston (1900) did not specify the number
of ridges as a diagnostic feature in his description, 12
ridges are discernable on the tooth shown as figure 7 of
Plate XXIX. Most of the other photographs of the other
teeth are not clear enough to count, however, the tooth
shown as figure 8 appears to have 7 ridges. Meyer
(1974) noted that the subspecies Ptychodus anonymus
anonymus from the Kamp Ranch Member (Turonian)
of the Arcadia Park Shale of Texas exhibited fewer
transverse ridges and noted the same concentric pattern
on the marginal area as is observed on AMNH 19553.
Specimens figured by Lucas et al. (1988, fig. 13A-D)
also display a variation in the number of ridges. Welton
and Farrish (1993, p. 57) indicate that the "crown is
moderately inflated; cusp conical, high and rounded;
transition from cusp to marginal area smooth, not
angular; approximately 12 fine transverse ridges extend
across apex, down sides of cusp, then divide and curl
around as they enter marginal area; margin narrow with
bumpy granular pattern, not crossed by transverse
ridges in marginal area; root anaulacorhizous;
histology osteodont." The teeth of AMNH 19553
match these descriptions in all aspects of tooth shape.
However, the teeth exhibit only 5 to 7 fairly coarse
transverse ridges, which extend downward, but not
completely to the bottom of the cusp. The marginal
area has a distinct pattern of fine, irregularly concentric
lines. Tooth ornamentation, including the number of
The number of Ptychodus species has increased
significantly since they were first described by Agassiz
(1833-1844). Because of this, and the poorly
understood relationships between these species, the
genus is certainly in need of further study and revision.
Many species of ptychodontids have one or more
subspecies (Dibley, 1911; Meyer, 1974). According to
Dibley, (1911), P. decurrens has four subspecies.
Meyer (1974) listed two sub-species for P. anonymus.
According to Meyer (Ibid.), Williston's original form is
now P. anonymus anonymus. It is joined by a smaller,
more primitive subspecies P. anonymus blechroconus.
Furthermore, Meyer (Ibid.) suggested that a transition
occurred over time from P. decurrens bifurcus to P.
anonymus blechroconus to P. anonymus anonymus.
However, Cicimurri (pers. comm., 2004) noted that the
large specimen of P. decurrens figured by Meyer is
more likely a high crowned P. occidentalis. Meyer
(1974) also indicated an apparent transition occurred
from the low to the high crowned species between the
Cenomanian and the Coniacian, and concluded that P.
decurrens is the most primitive form based on its low
crown height. The earliest occurrence of P. decurrens
in Kansas is near the contact of the Dakota Sandstone
133
PALUDICOLA, VOL. 4, NO. 4, 2004
134
transverse ridges, is similar to the description that
Welton an
d Farrish (Ibid.) provide for Ptychodus
mammillaris. However, the teeth of AMNH 19553 do
not exhibit the characteristic flattening of the crown
observed in P. mammillaris. Welton and Farris (1993)
disagreed with the suggestion by Herman (1977) that
P. anonymus is a subspecies of P. mammillaris. It
appears that AMNH 19553 has affinities of both
species, which would tend to support Herman’s
argument. Considering the amount of variation in tooth
morphology that has been reported, P. anonymus
appears to be a transitional form that clearly needs
more study.
CONCLUSION
AMNH 19553 is significant because: 1) it is the
m
ost com
plete set of remains of Ptychodus anonymus
yet described, including calcified vertebral centra,
replacement teeth and oral denticles; 2) the presence of
calcified centra indicates that ptychodontids are
neoselachians, and not hybodonts; 3) it is associated
with accurate stratigraphic information; and 4) it was
recovered near the upper end of the temporal range of
this species in the Western Interior Sea. In addition,
this specimen provides useful data on the temporal
distribution and diversity of the late Coniacian fauna in
the Western Interior Sea during the Late Cretaceous.
ACKNOWLEDGEMENTS
We thank Don Albin, Utica, KS, for allowing
access to the
locality; J. D. Stew
art, Los Angeles
County Museum of Natural History, for his analysis
and discussion of the matrix associated with the
specimen; and John Maisey, American Museum of
Natural History for his assistance in arranging the loan
of the specimen and for insightful conversation
concerning selachian dentitions. Larry Martin and
Desui Miao, University of Kansas Museum of Natural
History, provided access to Ptychodus specimens in
their care. Merle Graffam, Big Water, UT, and Jim
Bourdon, Croton on Hudson, NY, independently
provided information on Ptychodus species of the
Tropic shale of Utah. David Cicimurri, Bob Campbell
Geology Museum, Clemson University, and an
anonymous reviewer provided valuable comments
which greatly improved the content of this paper.
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