New Data on Cranial Measurements and Body Length of the Mosasaur, Tylosaurus nepaeolicus (Squamata; Mosasauridae), from the Niobrara Formation of Western Kansas

Abstract

Tylosaurus nepaeolicus (Cope 1874) is one of the least well known of the five species of mosasaurs that are recognized from the lower Smoky Hill Chalk Member (upper Coniacian) of the Niobrara Formation in western Kansas. In describing the type material, Cope stated that this species was one-third or less the size of T. proriger (Cope 1869), a species that appeared during the Santonian and is well represented in the middle and upper chalk. Additional data provided by Russell from a review of specimens in the American Museum of Natural History and the Yale Peabody Museum showed that most T. nepaeolicus material is somewhat larger than the type specimen, but is significantly smaller than adult T. proriger specimens. Measurements of two additional T. nepaeolicus skulls, an articulated series of Tylosaurus sp. vertebrae and other material in the Sternberg Museum of Natural History suggest that this species approached 8–9 m in size by the end of the Coniacian and was approximately the same size as a large T. proriger reported from the lower Santonian. Although time and other morphological features separate T. nepaeolicus from T. proriger, the two species are closer in size than previously reported.

Full text

TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE
105(1-2), 2002, pp. 33-43
New Data on Cranial Measurements and Body Length
of
the
Mosasaur, Tylosaurus nepaeolicus
(Squamata; Mosasauridae), from
the
Niobrara Formation of Western
Kansas
MICHAEL
J.
EVERHART
Sternberg
Museum
of
Natural
History,
Fort
Hays State
University,
Hays,
Kansas, 67601
e-mail:
meverhar @fhsu.edu
Tylosaurus nepaeolicus (Cope 1874) is one of the
least well known of
the
five
species
of mosasaurs
that
are
recognized
from the lower
Smoky
Hill
Chalk Member (upper Coniacian) of the Niobrara
Formation
in western
Kansas. In describing
the
type
material,
Cope stated
that this
species was
one-third
or
less the
size of T.
proriger
(Cope 1869),
a species
that
appeared
during
the
Santonian
and
is well
represented
in
the middle and
upper
chalk.
Additional
data provided
by Russell from a review of specimens
in the
American Museum of Natural History
and the Yale Peabody Museum
showed
that
most
T. nepaeolicus material
is somewhat
larger
than the
type
specimen,
but is significantly
smaller than
adult
T.
proriger specimens.
Mea-
surements
of two additional
T. nepaeolicus skulls,
an articulated series of
Tylosaurus
sp. vertebrae and other material
in the Sternberg
Museum of
Natural
History
suggest
that
this
species approached
8-9 m in size by
the
end of the
Coniacian and was approximately
the
same size as a large
T.
proriger
reported
from the lower
Santonian.
Although
time and other mor-
phological
features
separate
T.
nepaeolicus
from
T.
proriger,
the two
species
are closer
in size than
previously reported.
INTRODUCTION
Mosasaurs
(Squamata; Mosasauridae) are
extinct marine lizards that lived
during
the Late Cretaceous,
from the
Turonian
(Martin
and Stewart,
1977)
through
the Maastrichtian.
Their remains are
preserved
in
marine sediments
around
the world,
but are especially abundant
in the Smoky Hill Chalk
Member of the Niobrara Formation
in
western Kansas.
Between 1868 and 1874,
most of the mosasaur
species currently
consid-
ered
to
be valid from the
Smoky
Hill Chalk Member of
the
Niobrara For-
mation
in western Kansas (Everhart, 2001) were described
by
the 19th
Cen-
tury
Philadelphia
paleontologist,
Edward Drinker
Cope (1840-1897). These
include: the
genus
Clidastes
Cope 1868 and its
type species,
C. propython
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

34 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE
Cope 1869
(described
from the Alabama
chalk);
the
genus
Platecarpus Cope
1869 and its
type species, P. tynpaniticus Cope 1869, and P. planifrons
(Cope 1874); and the
type species of
Tvlosaurus,
T.
proriger
(Cope 1869),
the
first mosasaur described from
Kansas,
and T. nepaeolicus (Cope 1874).
The genus
Tylosaurus
Marsh
1872
has a complicated
history,
including
sev-
eral name
changes,
which is too convoluted
to be recounted
here,
save to
say that
Leidy (1873, p. 271) formally placed Macrosaurus
proriger
Cope
1869 into Tvlosaurus.
More than 125 years
after its first
description,
Tvlosaurus
nepaeolicus
remains
relatively
unknown.
T.
nepaeolictus
is
recorded
only
from
the lower
Smoky Hill Chalk Member (upper Coniacian) of the
Niobrara
Chalk in
Kansas. According
to records
in the
USNM (Smithsonian)
collection,
the
first known
specimen
of
Tvylosaurus
nepaeolicus probably
was collected
by
Dr.
George
Miller
Sternberg
(1838-1915), a U. S. Army surgeon
who was
stationed
at Fort Harker and
elsewhere
in
western
Kansas between
1866
and
1870. Dr. Sternberg,
the older brother of Charles
H. Sternberg,
is credited
with
at
least 40 other Kansas specimens
in the
USNM collection,
but is best
known
for
being
the
Surgeon
General of the United States from
1893-1902.
A mosasaur
premaxilla
(USNM V-3894) attributed
to Dr. Sternberg
was
figured by Leidy (1873, p. 275, pl. 35) and initially
identified as a T.
pro-
riger.
Russell (1967, p. 176) examined the material and considered
it
to be
T. nepaeolicus.
Cope (1874, p. 37-38) described
the
type specimen
of
Liodon
nepaeolicus
(AMNH 1565) from
material discovered
by
Professor
Benjamin
E Mudge
(1817-1879) in the
"gray
shale
of
the Niobrara
Cretaceous,
a half mile south
of the Solomon River," in north-central Kansas. The species name most
likely
comes from
"Nepaholla," an earlier Indian name for the
Solomon
River
(Solomon's Fork of the
Smoky
Hill
River)
meaning
"water
on
a hill"
(Rydjord,
1972,
p. 109).
Cope (1871, p.
416) earlier had described the
origin
of
material in the
Mudge collection as "from the
yellow
chalk of
the
upper
cretaceous
(sic) of Kansas on the
Solomon or Nepaholla River."
The type
locality
is uncertain but
probably
is near the town of Stockton,
in Rooks
County.
Mudge sent
specimens
to
Cope as early
as 1870
(Williston,
1898a,
p. 29-
30). During
his 1871 trip
to the
West,
Cope visited
Mudge at the Kansas
Agricultural College in Manhattan,
Kansas (now Kansas State
University)
and examined
Mudge's collection of mosasaur
and fish
specimens
(Cope,
1872). In 1874, Mudge and two assistants,
including
a young
Samuel W.
Williston
(1851-1918), began collecting "vertebrates for Yale College"
(Mudge, 1876,
p. 216; Williston,
1898a, p. 31). Between 1874 and 1876,
Mudge located
eight
additional
specimens
of
Tylosaurus
nepaeolicus
for
O.
C. Marsh and the YPM collection,
two of which also came from Rooks
County.
According
to the YPM records,
the others that he collected were
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

VOLUME 105,
NUMBERS 1-2 35
from:
Ellis County
(1 specimen), Trego
County
(3 specimens),
and Gove
County
(2 specimens).
The exposures
of the
Smoky
Hill Chalk Member
in
these counties
generally
are low in the
chalk (upper
Coniacian) with the
exception
of
parts
of northern
Trego County
and
western
Gove County
that
are lower to middle Santonian. These localities
are consistent with
the bio-
stratigraphic
occurrence
of T. nepaeolicus (Everhart,
2001, fig.
5; Schu-
macher, 1993,
p. 56).
According
to Cope (1874, p. 37), the
type specimen
of Tylosaurus
ne-
paeolicus (AMNH 1565) was represented by
a right
lower
jaw, parts
of the
maxilla and premaxilla,
a right quadrate
and a dorsal
vertebra. The 1874
description
was repeated
verbatim and illustrated
in Cope (1875, p. 177-
178,
pl. 35,
figs.
11-14). Mudge's field
measurement
of
the intact lower
jaw
(26 inches)
was published
by
Cope (1874, p. 37). The lower
jaw was sub-
sequently damaged and incomplete
by the time it was figured by Cope
(1875, pl. 35, fig.
13). Cope (1874, p. 38) included measurements of the
teeth,
the
quadrate
and the
vertebra,
and stated that
the
species was "not
more
than
one third the size or less" of
T.
proriger.
He also indicated that
the
type specimen
was not a "young
individual" of
T.
proriger
(Cope, 1874,
p. 37). The new material
described
here
places the
type
specimen
low in
the size range
of
T. nepaeolicus.
Following
the transfer of Macrosaurus
proriger
Cope 1869 and Liodon
dyspelor
Cope 1871 to
Tylosaurus
Marsh 1872 by Leidy (1873, p. 274 and
271 respectively),
Merriam
(1894, p. 24) placed Liodon nepaeolicus
Cope
1874 in Tylosaurus.
He also removed the Greek
dipthong (ar), spelling
the
species name "nepeolicus," and included the
name
in his
discussion
of
the
mosasaur skull without further
comment.
According
to E. Manning (pers.
comm.,
2001), if the
diphthong
was to be removed,
the
species
name
prob-
ably
should
have
been
changed
instead to "nepaolicus,
" following
the
place
name,
Nepaholla,
more
closely.
Williston
(1898b, p. 176) apparently ignored
the
spelling change
by
Mer-
riam
(1894) and
repeated
much
of
the
description provided
by
Cope (1874).
He further
suggested
that
"(t)he characters
given-such as may
be valid-
are
altogether
too slight
to
distinguish
the
species,
and
I do not believe
that
T. nepaeolicus is entitled
to recognition."
Stewart
(1990, p. 29) listed
T.
nepaeolicus
as one of
three
species
of mosasaurs
typical
of the lower
chalk
in
the
biostratigraphic
zone of
Protosphyraena pernicosa
(upper
Coniacian).
Russell (1967, p. 187; 1993,
p. 673) included
T.
nepaeolicus
as one of three
mosasaur
species
from the "low chalk." After
examining
the
type
specimen
(AMNH 1565), C. Kiernan
(pers. comm.,
2001) concluded
that it is not
sufficient
to serve as the basis for
a taxon
and,
in
fact,
is indeterminate.
Our
knowledge
of
Tylosaurus nepaeolicus
continues
to
be limited
by
the
lack
of
specimens.
Russell
(1967, table
A) provided
measurements
of several
skulls of T. nepaeolicus in the AMNH and YPM collections.
The most
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

36 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE
.pof-
" i)
"pf
sq
,l,,f f *`-
\,,
rl--
i~.-?h,
-??*UI~lllllll4N
Figure 1. Reconstructed
skull and jaw of Tylosaurus
nepaeolicus in right
lateral
view
(adapted
from Russell (1967), after
AMNH 124 and 134): Abbreviations:
a, angular;
ar,
artic-
ular;
c, coronoid; d, dentary;
e, epipterygoid;
f,
frontal;
j, jugal; m,
maxilla;
p, parietal;
pm,
premaxilla;
pof, post-orbitalfrontal;
pr, prootic; prf,
prefrontal;
pt, pterygoid; q, quadrate;
sa,
surangular;
sp,
splenial; sq, squamosal;
st;
supratemporal.
Adapted
from
text-figure
95 in Russell
(1967).
complete
set
of
measurements is
actually
from
a composite
of two
specimens
(a complete
skull,
AMNH 124; and lower
jaws, AMNH 134) that Russell
(pers.
comm.,
2001) believed
probably
were from the
same individual
(Fig.
1). The length
of
the skull
measured
along
the
midline
is 717 mm
(from
the
tip
of
the
premaxilla
to
the
back of
the
occipital condyle)
and the
length
of
the
lower
jaw is 828 mm.
A larger
but less complete
skull (YPM 3980,
collected
by
Williston in 1875) has an estimated skull
length
of about
860
mm.
Measurements of
the
length
of the lower
jaw of two
complete speci-
mens
of
T.
proriger
(AMNH 221 and
FHSM VP-3) indicate that it is about
14% of the
body
length.
Using
this ratio as a starting
point,
the
two
largest
T. nepaeolicus specimens
in the AMNH and YPM collections
would rep-
resent
living
mosasaurs that
were
about 5.9 m (19 ft)
and 6.8 m (21 ft)
in
length,
respectively.
The largest
T.
proriger
(AMNH 221) cited
by
Russell
(1967, p. 210) measured
just under 9 m (29 ft)
long,
or about one third
larger
than
the
largest
T. nepaeolicus
that he documented.
Given that
there
was an even larger
T.
proriger
specimen
known at the
time
(the 12-13 m
"Bunker" Tylosaur
(KUVP 5033) at the
University
of Kansas Museum of
Natural
History,
collected
in 1911 from
the
upper
chalk of Logan County
by
C. D. Bunker,
University
of
Kansas), it is certainly
understandable that
T. nepaeolicus would have been considered to be a smaller
species of Ty-
losaurus.
Measurements
of two more
recently
discovered
Tylosaurus
nepaeolicus
skulls in the Fort
Hays Sternberg
Museum
(FHSM) collection are
provided
here to update
the
size data available for this
species,
and to report
what
seems
to
be the
intergradation
in
size of
T.
nepaeolicus
and
T.
proriger
from
the
upper
Coniacian into
the lower
Santonian.
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

VOLUME 105,
NUMBERS 1-2 37
INSTITUTIONAL ABBREVIATIONS
AMNH, American
Museum of Natural
History,
New York,
NY; FFHM:
Fick
Fossil and
History
Museum,
Oakley,
KS; FHSM, Fort
Hays State Uni-
versity
Sternberg
Museum of
Natural
History, Hays,
KS; KUVP, The Uni-
versity
of
Kansas,
Museum of
Natural
History,
Lawrence,
KS; USNM, Unit-
ed States
National
Museum,
Washington,
D.C.; YPM, Peabody
Museum of
Natural
History,
Yale University,
New Haven,
CT.
SYSTEMATIC PALEONTOLOGY
Order
Squamata Oppel, 1811
Family
Mosasauridae
Gervais,
1853
Genus Tylosaurus
Marsh,
1872
Type species Tylosaurus
nepaeolicus (Cope, 1874)
DISCUSSION
The calculation of a maximum
adult
size for
any species
from data in
the
fossil record
is questionable
at best because it is not
always possible to
obtain
representative
samples. Many
collections
include
various
age groups
of
individuals
representing
a growth
series.
In mosasaurs,
growth
also prob-
ably
was indeterminate,
with
individuals
growing throughout
their
life,
albeit
at a slower
pace as they
got older.
Additionally,
there
was a natural bias
favoring
the
preservation
of
larger specimens
in
the
Smoky
Hill
Chalk Mem-
ber and there has been a human
bias for
collecting
and reporting
of the
largest
and best
preserved
individuals.
Measurements
obtained from a small
sample
of
individuals
may
be statistically
invalid,
as well as being
nonrep-
resentative of the
population
being studied. In the situation
of Tylosaurus
nepaeolicus,
the
total number of
curated
specimens
is certainly
fewer
than
30, 13 of which
are in the YPM collection. Nine additional
specimens
are
in the
United States
National Museum (Smithsonian)
collection. Several of
these
specimens
consist of one or a small
number of
bones
whose identifi-
cation may be questionable.
Limited data are available on the skulls of
eleven of
the
specimens
(Cope, 1874; Russell, 1967; this
report).
With
the
possible exception
of YPM 124/134,
there
are no complete
skulls and no
reasonably
complete
skeletons
of
this
species. Tylosaurus
proriger,
on the
other
hand,
is well represented
by dozens of skulls and many complete
specimens
in
museums
around the
world.
Although
fragmentary
remains of mosasaurs from
Kansas first occur in
Turonian rocks
(Martin
and
Stewart,
1977),
the
earliest
known remains iden-
tifiable to species occur
in the
Smoky
Hill Chalk Member
of
the
Niobrara
Formation
(upper
Coniacian-lower
Campanian). Tylosaurus
nepaeolicus
is
one of five mosasaur species identified from the
upper
Coniacian of the
Western
Interior Sea (Everhart,
2001). T. nepaeolicus shared
the
shallow
ocean that
covered
Kansas with
Platecarpus
tympaniticus
(including
the
ju-
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

38 TRANSACTIONS OF THE KANSAS
ACADEMY
OF SCIENCE
nior
synonyms
P. ictericus
and P. coryphaeus),
P. planifrons,
and Clidastes
liodontus
Merriam
1894 (Everhart,
Everhart,
and Bourdon,
1997) and an-
other,
undescribed
primitive species of Tylosaurus
(Stewart,
1990; Schu-
macher, 1993; Sheldon, 1996; Bell, 1997). Platecarpus
tympaniticus
and C.
liodontus
both continue into
the
upper
chalk but the two
early
Tylosaurus
species seem to be replaced by T. proriger
in the lower Santonian.
Plate-
carpus planifrons
is not recorded
past
the
lower
Santonian
(Everhart,
2001,
p. 73-75). The earliest known T.
proriger
(FFHM 1997-10)
was discovered
in the
Smoky
Hill Chalk Member
(middle Santonian)
of Gove County
in
1996 (Everhart,
2001,
p. 71-73). The well-preserved, completely
articulated
skull
is 1.2 m in length,
with a total
body length
estimated
at 8.7 m (28.5
ft.).
Clidastes
propython
occurs for the first time
in the middle
Santonian
of
the
Smoky
Hill Chalk Member
(Schumacher,
1993; Sheldon,
1996). Speci-
mens
of
other
species, including
Halisaurus sternbergi
(Wiman 1920) and
Ectenosaurus clidastoides
Russell 1967,
are too rare
to
determine their
rang-
es, save to
say
that
they apparently
are
restricted to the
upper
chalk.
Mudge collected
extensively
from
Rooks,
Ellis, Trego
and eastern
Gove
counties between
1874 and 1876 (Williston,
1898a,
p. 31) where
exposures
are
mostly
in
the lower half
of the chalk. On the
basis of his
experience
in
the
Niobrara,
Williston
(1897, p. 245-246) later observed that
vertebrate
remains were
ten times
more
abundant
in
the "shallow water,"
upper
chalk
than in the
"deeper water,"
lower
chalk
and spent
little time
collecting
in
the lower chalk. Most of the better
known
vertebrate
specimens currently
in
museum
collections
come
from the
upper
half of the chalk in western
Gove,
Logan, and Wallace counties
(Bennett, 2000). Considering
that
Mudge col-
lected a disproportionate
number of the known
specimens
of Tylosaurus
nepaeolicus
during
the time he spent
in these low chalk
exposures,
it seems
that
a subsequent
collecting
bias against
low chalk localities
may partially
account
for the lack of
specimens
of this
species.
Tylosaurus
nepaeolicus differs
from
T. proriger
in the size and location
of the
parietal
foramen
(larger,
closer to the
frontal-parietal
suture
in the
latter),
the
size of the
infrastapedial
process
on the
quadrate
(larger
in T.
proriger),
the
lateral
overlap
of the
anterior
postorbital
frontal
over the
pre-
frontal
(absent
in T. nepaeolicus), and other features
(Bell, 1997, p. 297-
310). Until
recently
(Everhart,
2001), the two species also were
separated
chronologically by
a gap of
about 2 million
years
in the
fossil record
(upper
Coniacian-upper
Santonian).
Two specimens of Tylosaurus nepaeolicus in the Sternberg
Museum
(FHSM VP-2209 and VP-7262) collected after
Russell's (1967) publication
are
significantly larger
than the
type
specimen
and
most of
the material cited
by Russell (1967, p. 209). FHSM VP-2209 was collected
in 1966 by M.
Walker
and O. Bonner
from near
Glade, in
Phillips County,
Kansas (Schu-
macher, 1993,
p. 40). The specimen
includes both
maxillae,
the
frontal,
the
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

VOLUME 105,
NUMBERS 1-2 39
anterior
portion
of
the
parietal,
both
squamosals,
the
quadrates,
both man-
dibles,
cervical and dorsal
vertebrae,
and some limb elements.
According
to
J.
D. Stewart
(Schumacher,
1993,
p. 40), the site was in
the
biostratigraphic
zone of Protosphyraena
pernicosa (upper Coniacian). VP-7262 was col-
lected
in southeastern Gove County by
R. J. Zakrzewski in 1984 from near
Hattin's
(1982) Marker Unit 5 (upper
Coniacian). The remains
consist of
the
premaxilla, complete right
and left
maxillae,
the
complete
frontal,
a large
fragment
of
the
posterior parietal,
the
left
quadrate,
both
pterygoids, portions
of both lower
jaws including
the
complete
left
dentary,
and numerous ver-
tebrae.
Many small fragments
of shattered
bone were collected at the
site
and it is possible
that the skull
was essentially
complete prior
to
weathering.
The same measurements
reported
by
Russell (1967, p. 210) are
provided
for both
of
the
new
specimens
(Table 1). Russell
(1967) determined that the
length
of a Tylosaurus
skull
averaged 13.8% of the total
body length.
In
practice,
the length
of the lower
jaw is about 14% of the body length
(AMNH 221 and FHSM VP-3). Because this
measurement is available more
readily
for
the
less complete specimens
of T. nepaeolicus, it
was used to
estimate total
body length
(Table 1,
column
I). In situations where
only
the
length
of the
dentary
was available (FHSM VP-7262), it
was considered to
represent
56% of
the
length
of the lower
jaw. Based on
similar measurements
of
the width
of
the frontal between
the
orbits,
the
length
between the anterior
base of the first and the
posterior
base of
the sixth
maxillary
tooth,
and the
height
of the
quadrate,
the estimated
body lengths
for YPM 3980 and FHSM
VP-7262 are identical
(6.8 m, 22 ft),
with
VP-7262 representing
a more
complete specimen.
With a lower
jaw length
of 1
m
(3.3 ft),
VP-2209 seems
to be the
largest
T. nepaeolicus
known,
fully
half
again
as large
as the
type
specimen.
VP-2209 represents
at 7.1 m (23 ft)
individual
from near
the
Coniacian/Santonian
boundary.
Three other
specimens
in the
Sternberg
Museum collection are relevant
to this
discussion. FHSM VP-2295 is a completely
articulated skull and
lower
jaws of the undescribed
species of Tylosaurus
(lower
jaw length
=
720 mm).
The specimen
was recovered from the low chalk
(upper
Conia-
cian) of Ellis County,
8 miles northeast of
Ellis,
by
M. Walker
(FHSM) and
represents
a 5 m (16 ft)
adult.
The frontal and right dentary
have several
long, deep gouges
and
punctures
that seem to be unhealed bite marks from
an
fatal encounter
with
a larger
mosasaur.
These bites
are not
typical
of
large
sharks such
as Cretoxyrhina
mantelli
and there are no other
predators
doc-
umented
from the Western Interior Sea besides mosasaurs that could have
inflicted these
types
of
wounds on a 5 m Tylosaurus.
FHSM VP-13742 is a large
but
badly
weathered skull of an as yet
un-
identified
Tylosaurus
(Everhart, 1999) discovered within
0.5 km of the lo-
cality
in Gove County
that
produced
FHSM VP-7262, and at
approximately
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

Table 1. Selected measurements
(mm) of
Tylosaurus
nepaeolicus and T.
proriger
skulls.
Tylosaurus
nepaeolicus: A B C D E F G H I
AMNH 1565 (Type) (1) 82 660 4700*
AMNH 124 and 134 (2) 717 19 116 176 91 828 444 180 5900*
YPM 3980 (2) 142 181 110 6800*
FHSM VP-7262 40 140 180 108 530 173 6800*
FHSM VP-2209 170 205 130 1000 580 210 7100*
Tylosaurus
proriger: A B C D E F G H I
USNM 6086 (2) 585** 118 142** 79 650 373 163 4200*
AMNH 4909 (2) 600 29 113 146 78 686 402 143 4900*
USNM 8898 (2) 710 223** 935** 565 215 6700*
AMNH 221 (3) 160 8300
FFHM 1997-10 1016 61 190 284 150 1220 667 251 8700*
FHSM VP-3 1080 60 180 250 150 1230 660 230 8800
KUVP-1032 (2) 1195 9900*
A = Length
of skull
along midline;
B = Length
of
premaxilla
rostrum;
C = Width of frontal
between
orbits;
D = Length
between
first
and
sixth
maxillary
tooth;
E = Height
of
quadrate;
F = Length
of lower
jaw; G = Length
of
dentary;
H = Length
between first and sixth
dentary
tooth;
I - Calculated
length
of
body (14% of
lower
jaw length);
*
Estimated,
this
paper; ** = approximate.
Measurements
by (1) Cope (1874);
(2) Russell
(1967); (3) Osborn
(1899).
4x
0
z
H
0
z
0
ia
H
z
z
>3
>
>
?~
O
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

VOLUME 105,
NUMBERS 1-2 41
the
same stratigraphic
level (upper
Coniacian). The lower
jaws measure
98
cm (39 in),
suggesting
a mosasaur of about 7 m (23 ft)
in
total
length.
FHSM VP-13908 is a series
of 14 articulated
Tylosaurus
vertebrae
from
below Hattin's
(1982) Marker
Unit
4 (upper
Coniacian) in Gove County.
Although
the
species
cannot be identified
reliably
from characteristics of the
vertebrae,
there is no reason to
expect
that it would be anything
other than
T.
nepaeolicus
or,
less
likely,
the undescribed
species
of
Tylosaurus
(Stewart,
1990; Schumacher,
1993; Bell, 1997). The vertebrae were discovered
in
1989 by my
wife,
Pamela Everhart,
eroding
from the
edge of a dry
stream
bed. They
were located
within
sight
(about
200 m) of the
FHSM VP-7262
locality,
but are from a slightly
lower
stratigraphic
level. The vertebrae are
identified as posterior
dorsals and pygals. Although laterally
compressed
somewhat
during preservation,
they
are similar
in length
(110 mm) and
diameter
to those of FHSM VP-3 (an 8.8 m
T.
proriger). By comparing
the
length
of the articulated
segment
(1.4 m) and the calculated
percentage
of
this
vertebral
segment
to the
length
of a complete
8.8 m
Tylosaurus
skeleton
(FHSM VP-3) from the
upper
chalk
(lower
Campanian),
a length
of
8-9 m
was estimated.
This length
is comparable
to the calculated
body size of
another
T. proriger
(FFHM 1997-10) from the middle Santonian
of Gove
County.
CONCLUSION
Since
its
description
in 1874,
Tylosaurus nepaeolicus
has been considered
to be significantly
smaller
than
T.
proriger.
The lack of
complete specimens
of T. nepaeolicus seems to have discouraged
further
studies of this taxon.
Although
it remains one of the lesser known
mosasaurs from the lower
Smoky
Hill Chalk Member
in Kansas, a sufficient number of specimens
now is available to
provide
a more accurate assessment
of its size range
in
comparison
to T. proriger.
New material shows
that adults of this
species
were significantly
larger
than the "one third" of the size of T. proriger
originally
estimated
by Cope (1874) or even the
specimens
measured
by
Russell (1967). In addition,
large
vertebrae from the lower
one-third of the
Smoky Hill Chalk Member (upper
Coniacian) indicate the
presence
of a
Tylosaurus
that
was about
8-9 m in
body length.
Although
minor
morpho-
logical features
separate
the two
species,
the fossil record
indicates
clearly
that
by
the end of the Coniacian (86 mya)
T. nepaeolicus
was approaching
the same
adult size observed
in
T.
proriger
remains from
the lower to middle
Santonian
and later.
ACKNOWLEDGMENTS
I thank
Dwayne and Marion Cheney,
of Bellevue, NE, and Glenn and
Arlene Bird of Quinter,
KS, for
allowing
me access to their
property,
and
for the donation
of some of
the
specimens
discussed
in
this
paper. Many
of
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

42 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE
the
specimens
and much of the
biostratigraphic
information
reported
in this
study
would not have been available without their
cooperation
and encour-
agement.
I thank
Donald Hattin
(Department
of
Geology,
Indiana
University,
Bloomington,
IN) and J.
D. Stewart
(Los Angeles County
Museum of Nat-
ural
History,
Los Angeles,
CA) for their
help
during
the
years
in understand-
ing the
stratigraphy
and paleontology
of the
Smoky
Hill Chalk Member.
I
thank
Dale Russell (North
Carolina State
University,
Raleigh,
NC) for his
insight
into this
paper and our ongoing
discussions about mosasaurs.
The
assistance of Robert
Purdy
and Michael Brett-Surman
(United States
Na-
tional
Museum,
Washington,
D.C.) in obtaining
historical
records on early
mosasaur collections is appreciated.
The advice and continued
support
of
Jerry
Choate,
Rick
Zakrzewski,
and Greg Liggett
at
the
Sternberg
Museum
of Natural
History, Hays, KS, also is appreciated.
I thank Earl Manning
(Geology Dept., Tulane Univ., New Orleans) for his review of the draft
manuscript,
his assistance in obtaining
reference
material and his views on
the historical context
that
guided the discoveries made by 19th
Century
paleontologists
in Kansas. I also thank C. Kiernan
for
her review and com-
ments. John
Jagt
and Anne Schulp (Natuurhistorisch
Museum Maastricht,
Maastricht,
The Netherlands)
provided
helpful
comments
on the final draft
of the
manuscript.
Ben Creisler
provided
the reference material
on
the
origin
of the
species name "nepaeolicus."
LITERATURE CITED
Bell, G. L. 1997. A phylogenetic
revision of North American
and Adriatic Mosasauroidea.
Pages 293-332 in Callaway J.
M., and E. L. Nicholls, eds., Ancient
Marine
Reptiles,
Academic Press,
San Diego.
Bennett,
S. C. 2000. Inferring stratigraphic position
of fossil vertebrates from the Niobrara
Chalk of western Kansas. Current Research in Earth
Sciences, Kansas Geol. Survey
Bull. 244(1): 1-26. (http://www.kgs.ukans.edu/Current/2000/bennett
l.html)
Cope, E. D. 1868. On some Cretaceous
reptilia.
Proc.
Acad. Nat. Sci. Philadelphia
20:233-242.
Cope, E. D. 1871. On the
fossil
reptiles
and fishes of
the
Cretaceous
rocks of Kansas. Art.
6,
Pages 385-424 of Pt.
4, Special Reports,
4th Ann.
Rept.,
U.S. Geol. Survey
Terr.
(Hay-
den), 511 p.
Cope, E. D. 1872. Note of some Cretaceous Vertebrata
in the
State Agricultural
College of
Kansas. Proc.
Am. Phil. Soc. 12(87):168-170.
Cope, E. D. 1874. Review of
the
vertebrata
of the Cretaceous
period
found
west of the Mis-
sissippi
River.
U. S. Geol. Survey
Terr. Bull. 1(2):3-48.
Cope, E. D. 1875.
The Vertebrata
of the
Cretaceous
formations of the
West.
Report,
U. S. Geol.
Survey
Terr.
(Hayden). 2, 302 pp.,
57 pls.
Everhart,
M. J. 1999. Evidence of feeding
on mosasaurs
by the Late Cretaceous lamniform
shark,
Cretoxyrhina
mantelli
(abst.). Jour.
Vert.
Paleontology
17 (suppl.
to
3):43A-44A.
Everhart,
M. J. 2001. Revisions to the
biostratigraphy
of
the Mosasauridae (Squamata) in the
Smoky
Hill Chalk Member
of'the
Niobrara
Chalk (Late Cretaceous)
of
Kansas. Kansas
Acad. Sci. Trans
104(1-2):56-75.
Everhart,
M. J.,
P. A. Everhart,
and J.
Bourdon. 1997. Earliest documented occurrence of
the
mosasaur,
Clidastes liodontus,
in the
Smoky
Hill Chalk (upper
Cretaceous) of western
Kansas (abst.). Kansas Acad. Sci. Abstract Vol. 16:14.
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions

VOLUME 105,
NUMBERS 1-2 43
Hattin,
D. E. 1982. Stratigraphy
and
depositional
environment
of the
Smoky
Hill Chalk
Mem-
ber,
Niobrara Chalk (Upper
Cretaceous)
of the
type
area,
western
Kansas. Kansas Geol.
Survey
Bull. 225, 108 pp.
Leidy,
J. 1873. Contributions to
the extinct vertebrate
fauna
of the western interior
territories.
Rept.,
U.S. Geol. Survey
Terr.
(Hayden) 1,
358 pp.,
37 pls.
Marsh,
O. C. 1872. Note
on Rhinosaurus.
Am.
Jour. Sci. 4(20):147.
Martin,
L. D., and J. D. Stewart. 1977. The oldest
(Turonian)
mosasaurs
from Kansas. Jour.
Paleontology
51(5):973-975.
Merriam,
J. C. 1894. Ueber die Pythonomorphen
der Kansas-Kreide.
Palaeontographica,
41:1-
39, 4 pls.
Mudge,
B. E 1876. Notes
on the
Tertiary
and Cretaceous
periods
of
Kansas. Bull.,
U.S. Geol.
Survey
Terr.
(Hayden),
2(3):211-221.
Osborn,
H. E 1899.
A complete
mosasaur
skeleton,
osseous and
cartilaginous.
Mem. Am. Mus.
Nat. Hist. 1(4):167-188.
Russell, D. A. 1967. Systematics
and morphology
of
American mosasaurs
(Reptilia,
Sauria).
Yale Univ.
Bull. 23, 241 pp.
Russell,
D. A. 1993. Vertebrates
in
the Western Interior Sea. Pages 665-680, in
Caldwell,
W.
G. E., and E. G. Kauffman, eds.,
Evolution of the Western Interior
Basin,
Geol. Assoc.
Canada. Spec. Paper
39.
Rydjord,
J.
1972. Kansas place names. Univ. Oklahoma
Press,
Norman,
OK. 613 pp.
Schumacher,
B. A. 1993. Biostratigraphy
of Mosasauridae (Squamata, Varanoidea)
from the
Smoky
Hill Chalk
Member,
Niobrara
Chalk (Upper
Cretaceous)
of
western Kansas. un-
publ. masters
thesis,
Fort
Hays State
Univ.,
Hays,
68 pp.
Sheldon,
M. A. 1996. Stratigraphic
distribution of mosasaurs
in the Niobrara Formation of
Kansas. Paludicola 1(1):21-31.
Stewart,
J.
D. 1990. Niobrara Formation vertebrate
stratigraphy.
Pages 19-30, in Bennett,
S.
C., ed., Niobrara
Chalk Excursion Guidebook. Univ. Kansas Mus. Natural. Hist. and
Kansas Geol. Survey.
Williston,
S. W. 1897. The Kansas Niobrara Cretaceous.
Pages 237-246, pls. 33-36. Kansas
Univ. Geol. Survey,
2, 318 pp.,
48 pls.
Williston,
S. W. 1898a. Addenda to Part
I [A history
of fossil
collecting
in western
Kansas,
from
1868-1898]. Kansas. Univ. Geol. Survey,
4:28-32.
Williston,
S. W. 1898b.
Mosasaurs. Kansas Univ. Geol. Survey,
4:81-221.
Wiman,
C. J. 1920. Some reptiles
from the Niobrara
group
in
Kansas. Bull. Geol. Inst.
Uppsala
18:9-18, 9 figs.,
pls. 2-4.
This content downloaded from 99.116.175.134 on Wed, 23 Oct 2013 15:20:57 PM
All use subject to JSTOR Terms and Conditions