Medial Cretaceous vertebrates from the Cedar Mountain Formation, Emery County: The Mussentuchit local fauna

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ABSTRACT
The upper Cedar Mountain Formation, Emery Coun-
ty, Utah, has yielded a rich vertebrate fauna including
nearly 80 taxa of Chondrichthyes, Osteichthyes, Lissam-
phibia, Reptilia, Aves, and Mammalia. High-precision
radiometric dating has established the age of the fauna as
latest Albian-earliest Cenomanian, placing it on the
Early-Late Cretaceous boundary. Although most of the
taxa remain to be studied in detail, the dense paleonto-
logic sampling and high diversity of the fauna, coupled
with the fact that its age is well established, suggest that
it will provide a benchmark for study of terrestrial biota
in North America during this key time interval, which
corresponds to the early radiation of angiosperm plants.
The vertebrate assemblage from the upper Cedar
Mountain Formation, herein named the Mussentuchit
local fauna for the area that has produced most of the
known sites, is clearly of Late Cretaceous aspect, indicat-
ing that the broad pattern of faunal composition for the
last half of the Cretaceous in North America was estab-
lished by the beginning of that epoch. Accordingly, the
Mussentuchit local fauna includes a number of first
North American or global appearances, notably varanoid
lizards; hadrosaurid, tyrannosaurid, and pachycephalos-
aurid dinosaurs; marsupial mammals; and snakes. Also
present are representatives of a number of archaic
groups, including the last sauropod in North America
(prior to reintroduction through immigration from South
America in the latest Cretaceous); triconodont and sym-
metrodont mammals; and several other taxa, such as the
turtle Glyptops.
The Mussentuchit local fauna differs from Early Cre-
taceous assemblages of North America and Europe, and
instead shares a number of taxa with Asia: although the
continent of origin cannot be confidently established for
many of the groups from the Mussentuchit local fauna,
existing evidence suggests an Asian origin for some of
the fauna, at least. The herbivore fauna is dominated by
one extremely abundant hadrosaurid; diversity of large-
bodied herbivores is low, in contrast to succeeding fau-
nas of the Campanian and Maastrichtian.
INTRODUCTION
Introductory Remarks
The Cedar Mountain Formation, named for terrige-
nous sedimentary rocks lying between the Dakota and
Morrison Formations (Stokes, 1944, 1952), is broadly
exposed in central and eastern Utah; eastward, the unit is
laterally contiguous with the Burro Canyon Formation of
MEDIAL CRETACEOUS VERTEBRATES FROM THE CEDAR
MOUNTAIN FORMATION, EMERY COUNTY, UTAH:
THE MUSSENTUCHIT LOCAL FAUNA
Richard L. Cifelli
Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019
Randall L. Nydam
Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019
James D. Gardner
Department of Biological Sciences and Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
Anne Weil
Department of Integrative Biology, University of California, Berkeley, California 94720
Jeffrey G. Eaton
Department of Geosciences, Weber State University, 2507 University Circle, Ogden, Utah 84408
James I. Kirkland
Utah Geological Survey, Box 146100, Salt Lake City, UT 84114-6100
Scott K. Madsen
Dinosaur National Monument, P. O. Box 128, Jensen, Utah 84035

western Colorado (see Stokes and Phoenix, 1948;
Tschudy and others, 1984; Mateer and others, 1992).
Two units of the Cedar Mountain Formation are general-
ly recognized, a lower Buckhorn Conglomerate (which is
variable in presence and thickness) and an overlying,
unnamed "shale" member (Stokes, 1952; Hale and Van
de Graaf, 1964). This upper member is 116 meters thick
in the type area, near Castle Dale, Emery County, though
generally thinner elsewhere. It is comprised of drab, var-
iegated mudstones, deposited on broad alluvial flood-
plains, together with thin channel sandstones (Young,
1960; Harris, 1980; Eaton and others, 1990). In places,
the mudstones are bentonitic (Young, 1960; Kowallis and
others, 1986). The lower part of the upper member of
the Cedar Mountain Formation, where it is present, is
characterized by abundant horizons containing caliche
nodules (for example, see Nelson and Crooks, 1987),
presumably representing seasonally dry paleosols. By
contrast, the upper part of the "shale" member generally
lacks nodular zones and instead has rare carbonaceous
layers (see Tschudy and others, 1984), with occasional
occurrences of amber.
Superpositional evidence has long favored a predom-
inantly Lower Cretaceous correlation for the Cedar
Mountain Formation (for example, Stokes, 1952), and
limited biostratigraphic evidence, in the form of freshwa-
ter invertebrates (Scott, 1987), palynomorphs (Tschudy
and others, 1984), and vertebrates (see below) seemed to
uphold this view. However, it has also been long estab-
lished that a significant time period lies between the
Morrison Formation (an Upper Jurassic unit) and the
Dakota Formation (of Cenomanian age), which bound
the Cedar Mountain Formation, and simple calculations
make it clear that complete representation of nearly 50
Ma in less than 150 meters of section is highly unlikely.
Recent evidence suggests the possibility of three separate
dinosaur faunas in the Cedar Mountain, separated by sig-
nificant hiatuses (Kirkland, 1996; Kirkland and others,
this volume)--one from a lowest part of the unit (perhaps
equivalent, in part, to the Buckhorn Conglomerate) pres-
ent only east of the San Rafael Swell, one from the
lower, nodular zone in the upper member of the Cedar
Mountain Formation, and the last from the upper part of
that unit. Our contribution is focused strictly on the ver-
tebrate fauna of the upper part of the upper member of
the Cedar Mountain Formation. Large-scale collecting
efforts, focused on a narrow stratigraphic interval about
10-20 meters below the contact with the overlying Dako-
ta Formation, have been conducted in the Cedar Moun-
tain Formation in Emery County, Utah, for the past ten
years, resulting in a densely sampled fauna. Radiometric
dates associated with the vertebrate fauna establish its
age as latest Albian-earliest Cenomanian (Cifelli, Kirk-
land, and others, 1997). Herein we describe the geo-
graphic, geologic, and stratigraphic context of this fauna,
and present the preliminary results of work in progress
on its constituent taxa.
Previous Work
Vertebrate Paleontology
Although the occurrence of fossil vertebrates in the
Cedar Mountain Formation had been noted by Stokes
(1944, 1952), the first published report describing such
materials is that of Bodily (1969), who recorded a
nodosaurid dinosaur from near Arches National Monu-
ment, in what is now interpreted to be the lower part of
the Cedar Mountain Formation. Further work in the
region was undertaken by paleontologists from Brigham
Young University, who made a large collection of
dinosaurs in the same part of the section from Dalton
Well--a site that is under active investigation by
researchers from Brigham Young University and the
Museum of Western Colorado. The only described mate-
rial we are aware of from this site belongs to the ornitho-
pod Iguanodon (see Galton and Jensen, 1979), but Britt
and Stadtman (1996) report a number of other taxa,
including a second ornithopod, a small nodosaur, three
theropods, and two sauropods. Recent investigations in
the lowest Cedar Mountain Formation east of Arches
National Monument have resulted in the discovery of
several dinosaurian taxa, of which only Utahraptor has
yet been described (Kirkland and others, 1993; see Kirk-
land and others, this volume). The most substantial
assemblage from the lower part of the upper member of
the Cedar Mountain Formation is that of the Long Walk
Quarry, east of Castle Dale, Emery County, which has
been under investigation by paleontologists from the
Utah Museum of Natural History. The material is mostly
undescribed, but the site evidently includes a massive
accumulation of a sauropod, perhaps Pleurocoelus, and a
theropod possibly similar to Acrocanthosaurus (DeCour-
ten, 1991).
The most notable early report of fossil vertebrates
from the upper part of the upper member of the Cedar
Mountain Formation is that of Jensen (1970), who
recorded the presence of several types of dinosaur
eggshell from southeast of Castle Dale. In 1983, paleon-
tological investigations in the upper Cedar Mountain
Formation were independently begun by one of us (JGE,
then of the University of Colorado) and by M. E. Nelson
(then of Fort Hays State University). As a result, several
preliminary investigations on the paleontology and
stratigraphy of the unit were produced and/or published
220 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah

Miscellaneous Publication 99-1 221Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
(Nelson and Crooks, 1987; Pomes, 1988; Eaton and oth-
ers, 1990; Eaton and Nelson, 1991). The primary sites
worked by these parties lie east of Castle Dale and Fer-
ron, Emery County, including Rough Road Quarry and
Robison's Eggshell Quarry--the latter of which has been
worked by a number of investigators, including Anthony
Fiorillo (then of the Carnegie Museum of Natural Histo-
ry) in 1991 (this volume) and us in 1992.
Age
There are no published reports that provide direct
evidence as to the age of the Buckhorn Conglomerate
and the lower part of the shale member of the Cedar
Mountain Formation. Stokes' original interpretation of a
Lower Cretaceous correlation for the Cedar Mountain
Formation was based largely on plant macrofossils said
to be abundant in other Lower Cretaceous units, such as
the Cloverly Formation (Stokes, 1952). At about the
same time, Katich (1951) reported several other fossils
from the type locality, including a fern, undetermined
ostracodes, and a bivalve believed to be of Aptian age.
Among the many plant macrofossils reported from the
Cedar Mountain Formation, perhaps the most noteworthy
are remains of angiosperm wood (Thayne and others,
1983, 1985), recovered from localities in the upper part
of the upper member, east of Castle Dale and Ferron.
Early angiosperms were generally low-statured; even
with the younger age now interpreted for the upper part
of the Cedar Mountain Formation (Cifelli, Kirkland, and
others, 1997; see below), this is some of the oldest evi-
dence for substantial woody tissue in flowering plants
(Wing and Tiffney, 1987).
Scott (1987) reported on freshwater bivalves from
the upper part of the Cedar Mountain Formation, which
he believed to be indicative of a middle Albian age. A
diverse assemblage of palynomorphs, also from the
upper part of the unit east of Castle Dale, was described
by Tschudy and others (1984). These authors considered
the flora to be of late Albian age, somewhat younger
than an assemblage obtained from the Burro Canyon
Formation, basing their interpretation on the appearance
of tricolporate pollen as a datum for the Upper Creta-
ceous. Nichols and Sweet (1993) indicated that tricolpo-
rates have a diachronous appearance in the Western Inte-
rior, and suggested that the assemblage reported by
Tschudy and others (1984) may be from lower Cenoman-
ian rocks.
Kowallis and others (1986) reported a 101 Ma age
peak and a 106 Ma conventional age, based on fission-
track dating of detrital zircons from what was interpreted
to be the Cedar Mountain Formation near Capitol Reef
National Park; these determinations are now considered
unreliable (B. J. Kowallis, written communication,
1994). The most recent geochronologic evidence for the
age of the upper part of the Cedar Mountain Formation,
presented by Cifelli, Kirkland, and others (1997), is sum-
marized below.
Abbreviations and Conventions
Abbreviations for institutions cited in the text: BYU,
Brigham Young University, Provo, Utah; CMNH,
Carnegie Museum of Natural History, Pittsburgh, Penn-
sylvania; FHSM, Fort Hays State University, Sternberg
Museum, Fort Hays, Kansas; MNA, Museum of North-
ern Arizona, Flagstaff, Arizona; OMNH, Oklahoma
Museum of Natural History, University of Oklahoma,
Norman, Oklahoma; UCM, Museum, University of Col-
orado, Boulder, Colorado; UMNH, Utah Museum of
Natural History, University of Utah, Salt Lake City,
Utah. Other conventions: AP, anteroposterior tooth
length; CT, computed tomography; LB, lingual-buccal
tooth width; m, meters; Ma, millions of years before
present.
VERTEBRATE PALEONTOLOGY OF THE
UPPER CEDAR MOUNTAIN FORMATION
Methods; Geographic and Stratigraphic
Distribution
The fauna reported herein was recovered as a result
of a large-scale collecting program by the OMNH and
includes most of the fossils collected between 1990 and
1996, although processing of some material remains
incomplete at this writing. Also included are mammalian
fossils obtained by one of us (JGE) while at UCM, and
non-multituberculate mammal specimens collected under
the direction of Michael Nelson while at FHSM. Virtual-
ly all mapped outcrops of the Cedar Mountain Formation
in the State of Utah were prospected during the course of
these investigations. Repeated attempts to find signifi-
cant accumulations of microvertebrates in the lower and
middle part of the unit were continually frustrated,
whereas the upper part of the "shale" member was re-
peatedly found to be productive, particularly in Emery
County. Here the outcrop of the Cedar Mountain Forma-
tion, like that of other Mesozoic units that are exposed in
the area, follows the flanks of the main structural feature
of the county, the San Rafael Swell (figure 1). Collect-
ing was conducted at 31 sites, including two worked by
previous investigators; most sites are near the headwaters
of Mussentuchit Wash, for which the local fauna reported
herein is named (figure 1). Collecting involved quarry-

ing for macrovertebrates and a combination of quarrying
and underwater screenwashing, with associated concen-
tration and recovery techniques, for microvertebrates
(Cifelli and others, 1996; Madsen, 1996). Articulated
remains of macrovertebrates are rare in the upper part of
the Cedar Mountain Formation. Accumulations of large
bone generally include representation of several taxa,
with occasional association of elements belonging to sin-
gle individuals. In general, the bone is highly friable;
original condition varies from pristine to highly water
worn. Microvertebrate specimens are similarly variable
in preservation; at the most productive site, OMNH
V695, abundant dissociated teeth occur together with
dentulous jaws and, rarely, skulls and articulated postcra-
nia. Most of the microvertebrate and macrovertebrate
localities appear to represent lag concentration of both
channel- and floodplain-derived materials, left in over-
bank deposits, although oxbow and other paleoenviron-
222 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
Figure 1. Emery County, Utah, showing exposure of the Cedar Mountain Formation (after Nelson and Crooks, 1987) and approximate positions of
OMNH fossil localities in the upper part of the "shale" member. Sites shown in inset, lower left, are in the immediate vicinity of Mussentuchit
Wash; tight clustering of sites 19-27, 29, and 31 precludes separate plotting of each at this scale. Bold-faced letters A-C refer to positions of
measured sections shown in figure 2 and described in the appendix. OMNH site numbers (see figure 2 for stratigraphic placement of representative
sites): 1, V213; 2, V214; 3, V234, 4, V235; 5, V236; 6, V237; 7, V238; 8, V239; 9, V240; 10, V694; 11, V695; 12, V696; 13, V794; 14, V795; 15,
V796; 16, V801 (=FHSM locality RRQ or Rough Road Quarry; see Nelson and Crooks, 1987; Eaton and Nelson, 1991); 17, V820 (=REQ or Robi-
son's Eggshell Quarry; see Nelson and Crooks, 1987; Eaton and Nelson, 1991; Fiorillo, this volume); 18, V823 (=MNA locality 1072; see Eaton
and Nelson, 1991); 19, V824; 20, V825; 21, V826; 22, V827; 23, V828; 24, V847; 25, V864; 26, V865; 27, V866; 28, V867; 29, V868; 30, V869;
31, V870.

ments are also represented.
Sections were measured so as to include the posi-
tions of all major localities; three sections through the
principal sites in the Mussentuchit Wash area, including
dated ash horizons, are shown in figure 2 (see also Nel-
son and Crooks, 1987) and are described in the appendix.
All sites fall within a narrow stratigraphic interval, 10 to
20 meters below the contact with the overlying Dakota
Formation (see figure 3). Laterally discontinuous, ben-
tonitic horizons representing volcanic ashes occur spor-
adically in the upper part of the upper member of the
Cedar Mountain Formation. One such horizon was dis-
covered immediately overlying the top of the bone hori-
zon at the most productive site, OMNH V695 (figure 4;
see also section A, figures 1, 2). Another such horizon,
probably but not certainly representing the same volcanic
event (see Cifelli, Kirkland, and others, 1997) occurs in
association with another locality about 6 km to the north-
east, in the same part of the stratigraphic column (section
C, figures 1, 2). Sanidine crystals extracted from these
horizons, including a total of four individual samples,
were submitted for radiometric dating using the single-
crystal 40Ar/39Ar single-crystal laser fusion method. The
determinations are strongly concordant and indicate a
mean age of 98.39 ± 0.07 Ma for the ash horizon and, by
implication, for the associated fauna of the uppermost
Miscellaneous Publication 99-1 223Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Figure 2. Measured sections, Cedar Mountain Formation, Emery County, Utah, showing stratigraphic positions of several key fossil localities and
dated ash samples (Cifelli, Kirkland, and others, 1997) in the area of Mussentuchit Wash. See figure 1 for approximate geographic positions of
sites and measured sections, and the appendix for descriptions of the sections.

224 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
Cedar Mountain Formation (Cifelli, Kirkland, and others,
1997). This age is not significantly different from the
Albian-Cenomanian (Early- Late Cretaceous) boundary,
currently placed at 98.5 Ma (Obradovich, 1993) and 98.9
± 0.6 Ma (Gradstein and others, 1995). Since these dates
were obtained, ash horizons (in the same part of the sec-
tion and possibly representing the
same volcanic event) have been iden-
tified in several other places, notably
in association with a newly discov-
ered and highly productive microsite
(OMNH V868; figure 3); additional
radiometric determinations are not
yet available.
The Mussentuchit Local Fauna
Nearly 80 taxa of fossil verte-
brates are now known from the upper
part of the Cedar Mountain Forma-
tion (table 1). Because all of these
are based on specimens from locali-
ties with a narrow stratigraphic and
geographic focus, we refer to this
assemblage as the Mussentuchit local
fauna. We do this in order to pro-
mote precision of reference in mak-
ing comparisons with other faunas, to
avoid lumping of (or confusion with)
temporally or geographically dissimi-
lar assemblages, and to aid in future
development of a biostratigraphic
framework (see, for example, Savage
and Russell, 1983; Woodburne, 1987;
Rowe and others, 1992). Work on
recovery and preparation of these fos-
sils is still ongoing, and the following
comments are offered in the form of a
preliminary report. Level of resolu-
tion for taxonomic identification is
highly variable and, in many cases,
low. This is due partly to inadequate
representation of diagnostic morphol-
ogy but also to the fact that the time
period represented by the Mussentu-
chit local fauna is otherwise virtually
unrepresented elsewhere, and that
significant hiatuses (about 10 Ma; see
Jacobs and others, 1991) separate it
from other reasonably well-known
faunas, such as those of the Cloverly
Formation, Montana and Wyoming
(Ostrom, 1970) and the Trinity
Group, northern Texas (Winkler and others, 1990). Many
taxa are probably new, an expectation that is supported in
the few cases in which detailed study has been undertak-
en (for example, Cifelli and Madsen, 1998). The faunal
list for the Mussentuchit local fauna (table 1) is based on
Figure 3. OMNH microvertebrate locality V868, Mussentuchit Wash area, upper Cedar Moun-
tain Formation, Emery County, Utah. The locality lies approximately in the center of the photo-
graph. The relatively homogenous character of the mudstones in the upper part of the unit is
apparent; the overlying Dakota Formation forms the resistant cap to the ridge in the background.
Figure 4. OMNH microvertebrate quarry V695, Mussentuchit Wash area, upper Cedar Mountain
Formation, Emery County, Utah. V695 has produced a number of the more informative microver-
tebrate specimens (see, for example, Cifelli, 1993a; Cifelli and Nydam, 1995) from the unit. The
dated ash horizon (Cifelli, Kirkland, and others, 1997) is indicated by an arrow.

Miscellaneous Publication 99-1 225Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Chondrichthyes
Hybodontiformes
Hybodontidae
Hybodus sp.
Polyacrodontidae
Polyacrodus parvidens
Lissodus spp. (2)
Orectolobiformes
Orectolobidae
n. gen. & spp. (2)
Rajiformes
Ischyrhiza sp.
Myliobatiformes
cf. Baibisha n. sp.
Osteichthyes
Neopterygii, indet.
gen. & spp. (2) indet.
Lepisosteiformes
?Lepisosteidae
gen. & sp. indet.
Pycnodontiformes
?Pycnodontidae
gen. & spp. (2) indet.
Amiiformes, indet.
gen. & sp. indet.
Dipnoi
Ceratodontidae
Ceratodus sp.
Lissamphibia
Incertae sedis
Albanerpetontidae
cf. Albanerpeton arthridion
gen. & sp. indet.
Caudata
Scapherpetontidae
gen. & spp. (2) indet.
Anura
Family indet.
gen. & spp. (4) indet.
Reptilia
Testudines
Baenidae
gen. & sp. indet.
Pleurosternidae
Naomichelys sp.
Glyptopsidae
Glyptops sp.
Squamata
Family indet.
n. gen. & sp.
Teiidae
cf. Peneteius sp.
gen. & sp. Polyglyphanodontinae.
?Scincidae
gen. & spp. (2) indet.
?Paramacellodidae
gen. & sp. indet.
?Necrosauridae
gen. & sp. indet.
?Helodermatidae
n. gen. & sp.
Serpentes
Aniliidae
Coniophis sp.
Crocodilia
Bernissartiidae
Bernissartia sp.
Goniopholididae
cf. Dakotasuchus sp.
Polydectes sp.
Atoposauridae
gen. & sp. indet.
Teleosauridae
Machimosaurus sp.
gen. & sp. indet.
Pholidosauridae
gen. & sp. indet.
Dinosauria
Dromaeosaurinae
gen. & sp. indet.
Veloceraptorinae
gen. & sp. indet.
Troodontidae
gen. & sp. indet.
cf. Paronychodon sp.
Family indet.
cf. Richardoestesia sp.
Tyrannosauridae
cf. Alectrosaurus sp.
?Brachiosauridae
cf. Astrodon sp.
Hadrosauridae
n. gen. & sp.
Hypsilophodontidae
cf. Zephyrosaurus sp.
gen. & spp. (2) indet.
Pachycephalosauridae
gen. & sp. indet.
Neoceratopsia
gen. & sp. indet.
Avialae
?Hesperornithiformes
gen. & sp. indet.
Order indet
gen. & sp. indet.
Mammalia
Triconodonta
Triconodontidae
Astroconodon n. sp.
n. gen. and spp. (2)
Multituberculata
Suborder incertae sedis
Family indet.
n. gen. & sp.
Suborder Ptilodontoidea
Family indet.
Paracimexomys robisoni
P. n. sp. (small)
P. n. sp. (large)
?P.bestia
?P. sp., cf. ?P. bestia
?P. n. sp.
n. gen. and sp.
Symmetrodonta
Spalacotheriidae
Spalacotheridium n. sp.
Symmetrodontoides sp.
n. gen. & sp.
Tribotheria
Picopsidae
gen. & sp. indet
Pappotheriidae
n. gen. & spp. (2)
Family indet.
n. gen. & sp.
Order indet.
Family indet.
Kokopellia juddi
Marsupialia
gen. & spp. (2) indet.
Table 1. Vertebrates of the upper part of the Cedar Mountain Formation: the Mussentuchit local fauna.

226 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
more than 5,000 catalogued specimens in the collection
of the OMNH, supplemented by some of the mammalian
fossils deposited at the UCM and the FHSM (see Eaton
and Nelson, 1991). Basic data for the OMNH catalog,
which includes all of the taxa reported herein, may be
accessed through the OMNH web site:
www.omnh.ou.edu.
Chondrichthyes
Several of the chondrichthyans known from the
Mussentuchit local fauna are widely ranging, relatively
undiagnostic taxa (for example, Hybodontiformes); Lis-
sodus is relatively common, but Hybodus is also known.
Notable occurrences include a new genus of Orectilobi-
formes, representing (to our knowledge) the earliest
appearance of the Orectolobidae; and the rajiform
Ischyrhiza, which is typical of Late Cretaceous assem-
blages and makes its first global appearance in this
fauna. Also noteworthy is the presence of a myliobati-
form remarkably similar to Baibisha, otherwise known
from slightly younger rocks in central Asia (see Nessov
and others, 1994) and, possibly, the somewhat older
Paluxy Formation of Texas (Kirkland, unpublished data).
Osteichthyes
The dipnoan Ceratodus, common in earlier assem-
blages, is represented by extremely rare dental plates in
the Mussentuchit local fauna; the last occurrence of this
relict taxon is in the overlying Dakota Formation (Kirk-
land, 1987; Eaton and others, this volume). Actinoptery-
gians are represented by abundant scales and vertebrae,
and rare skull bones; several specimens, such as OMNH
30173 (from OMNH locality V695), include articulated
scales. Despite the abundant material collected to date,
actinopterygians remain the most poorly understood
component of the Mussentuchit local fauna. Most of the
scales resemble those of lepisosteids and semionotids in
being ganoid and more or less rhomboidal in outline. In
view of Wilson and Chalifa's (1989) observations about
the taxonomic reliability of ganoid scales, we conserva-
tively identify these, for the present, as "Neopterygii,
indeterminate." A second neopterygian is probably rep-
resented by a tiny, rhomboid, ganoid scale, OMNH
33921, with a serrated posterior margin. All actinoptery-
gian vertebrae collected this far from the upper part of
the Cedar Mountain Formation are amphicoelous, but
they vary markedly in size and preserved morphology.
To what extent these differences reflect taxonomic, indi-
vidual, or ontogenetic variation awaits further analysis.
Lepisosteid fishes, so abundant and characteristic of Late
Cretaceous and Early Tertiary assemblages of North
America, are tentatively recognized from the Mussentu-
chit local fauna on the basis of isolated teeth; teeth also
possibly belonging to Lepisosteidae are known from the
somewhat older Trinity Group, Texas (Thurmond, 1974;
Kirkland, unpublished data; but see cautionary note by
Winkler and others, 1990). Given the fact that diagnostic
materials, such as opistocoelous vertebrae (which are
unique to lepisosteids among actinopterygians) have yet
to be recovered from either unit, however, we emphasize
that inclusion of Lepisosteidae in both faunas is highly
tentative.
Specimens include jaws and teeth representing at
least two kinds of pycnodontiforms, an extinct group of
marine and freshwater fish characterized by a pavement-
like durophagous dentition (for example, Nursall,
1996a,b). We tentatively refer these taxa to the Pycn-
odontidae; they are similar to certain freshwater taxa
known from the Morrison and Dakota formations of the
Western Interior (Kirkland, 1998). A diverse assemblage
of Early Cretaceous pycnodontiforms has been described
from the Trinity Group, Texas (Thurmond, 1974), but
detailed comparisons with the material from the Mussen-
tuchit local fauna remain to be made.
Additional tooth-bearing palatal and marginal bones
have conical teeth. One indeterminate dentary fragment,
OMNH 29794, preserves a single row of five subthe-
codont teeth and is perforated labially by several nutri-
tive foramina. A nearly complete right dentary, OMNH
31059, bears a single row of 13 elongate, conical teeth
and a prominent "coronoid process." Prepared in lingual
view, the fossil jaw resembles dentaries of the extant
amiiform Amia calva. Slightly older amiiform jaws
(Thurmond, 1974) and vertebrae (Bryant, 1987) have
been reported from freshwater and marine deposits of the
Trinity Group, and the group as a whole is known back
into the Jurassic (Grande, 1996). Given that the taxa list-
ed in table 1 almost certainly underestimate the diversity
of actinopterygians in the Mussentuchit local fauna,
comparisons with other fish assemblages from the Early
and Late Cretaceous of the Western Interior are best
deferred at present.
Lissamphibia
Lissamphibians are represented in the Cedar Moun-
tain Formation by isolated elements and rare, incomplete
skeletons. Preliminary work suggests that four taxa of
indeterminate frogs, two taxa of probable scapherpeton-
tid salamanders, and two albanerpetontid taxa are pres-
ent, making this one of the most taxonomically diverse
lissamphibian assemblages yet reported from the mid-
Cretaceous.
The most productive site for frogs in the Cedar
Mountain Formation, OMNH V695, has yielded isolated

Miscellaneous Publication 99-1 227Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
humeri, vertebrae, maxillae, squamosals, and frontopari-
etals, as well as two incomplete skulls and an incomplete
vertebral column with an associated ilium and humerus.
The articulated specimens are currently being prepared,
and they should prove useful both for associating isolat-
ed bones and determining the higher level affinities of at
least some of the frogs represented in the collection.
Preliminary study of fossils prepared to date suggests
that these frogs were at an archaeobatrachian level of
organization and that a moderately diverse assemblage is
represented (Gardner, 1995). The most compelling evi-
dence for the latter suggestion is the presence of four
maxillary morphs. These morphs differ in a variety of
features (for example, absolute sizes, proportions, orna-
mentation, lingual morphologies, and inferred patterns of
contact with other bones), which we suspect are indica-
tive of at least species-level differences. Similar maxil-
lae from elsewhere have been referred to the Pelobatidae
sensu lato, Discoglossidae sensu lato, and Gobiatidae
(for example, Roˆcek and Nessov, 1993; Gubin, 1993,
1996).
Based on a limited number of dentaries and one
trunk vertebra from OMNH V695, Gardner (1994)
reported the occurrence of a batrachosauroidid salaman-
der in the Cedar Mountain Formation. With the discov-
ery, from this same quarry, of better preserved examples
of these elements, as well as two atlantes, it is evident
that these fossils are more likely referable to the
Scapherpetontidae, a family of paedomorphic salaman-
ders known from the Campanian to early Eocene of
North America (for example, Estes, 1964, 1965, 1969a,
1981; Naylor, 1983; Naylor and Krause, 1981) and from
rocks of suspected latest Albian to Campanian age in
Middle Asia (Nessov, 1981, 1988). Dentaries and verte-
brae of batrachosauroidids and scapherpetontids are simi-
lar (for example, Estes, 1969a, 1981; Naylor, 1983; Nay-
lor and Krause, 1981), but as these two families are cur-
rently considered to be only distantly related (for exam-
ple, Estes, 1981; Naylor and Krause, 1981; Duellman
and Trueb, 1986) and these resemblances appear to be
largely convergent. The largest dentaries (OMNH
27130, 27394, 27401, 27888, and 28086) resemble those
of other scapherpetontids in being elongate, lacking a
dental gutter, in having a Meckelian groove that is elon-
gate anteriorly and deep posteriorly, and in the presence
of an anteriorly directed foramen below the posterior end
of the tooth row. Among known taxa, they most closely
resemble dentaries of Piceoerpeton (Paleocene to
Eocene, North America; Naylor and Krause, 1981, figure
3), especially in having a shallow, anteriorly acuminate
external depression and nonpedicellate teeth. Trunk ver-
tebrae resemble those of both batrachosauroidids and
scapherpetontids in having prominent, widely divergent
rib-bearing processes, an elongate, thin neural spine, and
a markedly elongate hyperapophyseal spine (Estes,
1969a; Naylor and Krause, 1981), but they more closely
resemble trunk vertebrae of unequivocal scapherpeton-
tids in having amphicoelous centra (they are opistho-
coelous in most batrachosauroidids) and cotyles that are
not infilled with calcified tissue (cotyles are infilled in
batrachosauroidids) (Estes, 1969a; Naylor and Krause,
1981). Two atlantal centra (OMNH 33919, 33920) are
tentatively referred to the Scapherpetontidae based on
their dorsoventrally compressed anterior cotyles, pres-
ence of an odontoid process, and lack of calcified tissues
infilling the posterior cotyle (Naylor, 1983). OMNH
33919 resembles atlantes of Piceoerpeton (Naylor and
Krause, 1981, figure 1I-K) and cf. Piceoerpeton (Maas-
trichtian, North America; Naylor, 1983, figures 1, 2A) in
having a reduced odontoid process and deeply concave
anterior cotyles that are subcircular in anterior outline;
whereas OMNH 33920 resembles atlantes of Lisserpeton
(Campanian to Paleocene, North America; Estes, 1965:
figures 2a, b) in having the anterior cotyles short and
broad in anterior outline, odontoid process not constrict-
ed at its base, and posterior cotyle deeply conical interi-
orly and laterally compressed in posterior outline. If the
dentaries and vertebrae described above from OMNH
V695 are correctly identified, these represent the geolog-
ically oldest North American scapherpetontids. Differ-
ences such as those noted above between the two atlantes
are usually considered diagnostic at the specific or gener-
ic level, suggesting the presence of two probable
scapherpetontid taxa in the Cedar Mountain Formation.
Jaws of albanerpetontids, a group of superficially
salamander-like, Middle Jurassic to Miocene probable
lissamphibians (Fox and Naylor, 1982; McGowan and
Evans, 1995) are readily identified by their highly pleu-
rodont, nonpedicellate, chisel-like, and faintly tricuspid
teeth. Dentaries and premaxillae have been collected
from various sites in the Cedar Mountain Formation,
with several of the former bones preserving the inter-
locking symphysial prongs that are unique for albaner-
petontids. Although most of the jaws are too fragmen-
tary to be identified below the familial level, the best
preserved specimens indicate that two albanerpetontid
taxa are present. The first of these is represented by
three tiny, isolated premaxillae (OMNH 27375, 27979,
and 27980), which in their preserved morphologies and
small size compare favorably with the holotype (Estes,
1969b, figure 2C-E) and referred premaxillae of Albaner-
peton arthridion, a species otherwise known from the
early to mid-Albian Antlers Formation of Texas (Fox
and Naylor, 1982) and Oklahoma (Cifelli, Gardner, and

228 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
others, 1997; Gardner, unpublished data). The second
taxon is known by a relatively large dentary (OMNH
27413) and a pair of large, fused premaxillae (OMNH
26222). These jaws are similar to certain of the dentaries
and premaxillae referred by Fox and Naylor (1982, fig-
ures 2d,e, 4a) to A. galaktion (early Campanian, Alberta),
but the jaws from the Cedar Mountain Formation almost
certainly represent a previously undescribed albaner-
petontid species (Gardner, unpublished data).
Testudines
Turtles of the Mussentuchit local fauna are unre-
markable. The archaic genus Glyptops, abundant in the
underlying Morrison Formation, is also known from the
overlying Dakota Formation, in which it makes its last
appearance (Eaton and others, this volume). The pleu-
rosternid Naomichelys, first described from the Aptian-
Albian Cloverly Formation of Montana (Hay, 1908) and
later reported from the penecontemporaneous (see
Jacobs and others, 1991) Trinity Group of Texas
(Ostrom, 1970; Langston, 1974), is commonly encoun-
tered in the uppermost Cedar Mountain Formation. This
turtle, with its distinctive, pustulate ornamentation, was
thought to be of biostratigraphic utility because of its dis-
tribution in the Cloverly Formation and Trinity Group
(Ostrom, 1970); however, based on OMNH collections,
it has a broad range in Cretaceous rocks of the Kaiparo-
wits region, southern Utah, where it makes its last
appearance in the lower Campanian Wahweap Formation
(Eaton and others, this volume). In addition,
Naomichelys has been reported from the Campanian
(Milk River, Foremost Formations) of Alberta (Brinkman
and Nicholls, 1991).
Squamata
The lizards of the Cedar Mountain Formation have
previously been reported on only briefly (Cifelli and
Nydam, 1995; Nydam, 1995) and their study is in
progress by one of us (RLN). Materials recovered to
date include jaws and jaw fragments, isolated teeth, ver-
tebrae, limb elements, and isolated osteoderms. No com-
plete skulls or skeletons have been recovered and articu-
lated materials are limited to a series of three trunk verte-
brae (OMNH 28125) and a broken dentary with an artic-
ulated splenial (OMNH 28069). In general the lizard
fauna of the Cedar Mountain Formation is moderately
diverse and is composed of taxonomic groups that are
known from other North American Cretaceous microver-
tebrate faunas, though none of the taxa recovered can be
assigned to known genera or species. The composition
(at least on a family level) of the lizards of the Cedar
Mountain Formation compares more closely to that of
significantly younger North American Late Cretaceous
lizard faunas (see, for example, Estes, 1964; Estes and
others, 1969; Estes and Berberian, 1970; Armstrong-Zei-
gler, 1980; Rowe and others, 1992; Gao and Fox, 1996)
than to slightly older Early Cretaceous faunas (for exam-
ple, Winkler and others, 1990), although the Early Creta-
ceous record is less well known. The lizard groups rec-
ognized from the Cedar Mountain Formation include the
?Paramacellodidae, Scincidae, Teiidae, ?Helodermatidae,
and ?Polyglyphanodontinae.
The most abundant lizard in the Cedar Mountain
Formation is a teiid known from nearly all of the sites in
which microvertebrates have been collected. Assignment
to the Teiidae is based on the widely open Meckelian
fossa and associated hypertrophied splenial of the
mandible, wide sulcus dentalis, thick deposits of cemen-
tum, and sub-circular resorbtion pits at the base of teeth
(Estes and others, 1988; Gao and Fox, 1991). Most sig-
nificant of known morphology in this lizard is the tooth
structure, in which there are conical, recurved anterior
teeth and transversely oriented, molariform, bicuspid
posterior teeth. This tooth pattern is similar to that of
Late Cretaceous Peneteius from the Hell Creek Forma-
tion (Estes, 1969c, 1983) and modern Dicrodon and
Teius from South America. The fact that this teiid
appears in localities worked both extensively (V695) and
minimally (V801) indicates that the abundance of the
fossils of this lizard is most likely reflective of its real
abundance and not of a collecting bias. It should be
noted here that the bicuspid pattern of posterior teeth in
this lizard was previously believed to be restricted to
only two, unrelated Cretaceous teiids, Peneteius and
Polyglyphanodon (Estes, 1969c, 1983), with the former
being viewed as the possible ancestor of the modern gen-
era Dicrodon and Teius. However, the teiid of the
Mussentuchit local fauna and other teiids now known
from various Late Cretaceous faunas indicate that this
pattern was widespread in teiids throughout the last half
of the Cretaceous (Nydam, work in progress).
Another teiid from the Cedar Mountain Formation is
known from only one specimen (OMNH 28067), a bro-
ken dentary from locality V695. Again, the specimen is
identified as a teiid based on the morphology of the den-
tary and teeth (see above). The teeth of this lizard are
anteriorly unicuspid and conical, and weakly tricuspid in
the posterior part of the toothrow. This tooth pattern is
common among North American Late Cretaceous teiids
and has been described in such taxa as Chamops, Lep-
tochamops, Meniscognathus (Estes, 1964, 1983; Gao and
Fox, 1996), Socognathus,Sphenosiagon, and Geron-
toseps (Gao and Fox, 1991, 1996; but see Denton and
O'Neil, 1995 for a brief contrasting view of the taxonom-

Miscellaneous Publication 99-1 229Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
ic status of the latter three taxa). However, the abraded
condition of the teeth and generally poor preservation of
the dentary precludes any immediate assessment of the
relationship of OMNH 28067 to other teiids.
The presence of a possible polyglyphanodontine teiid
in the Mussentuchit local fauna is suggested by two
specimens, a jaw fragment with a single tooth (OMNH
29771) and an isolated tooth (OMNH 32629), both from
locality V239. Like polyglyphanodontines described
from the Maastrichtian age North Horn Formation
(Gilmore, 1942, 1943, 1946), the tooth of OMNH 29771
superficially appears to be thecodont or even acrodont.
Fortunately, the jaw has been broken in such a way as to
demonstrate a pleurodont attachment of the tooth to the
lateral parapet of the jaw; moreover, the tooth base is
covered with a heavy deposit of cementum. Assignment
of OMNH 29771 and 32629 to the Teiidae is based on
the heavy deposit of cementum at the base of the tooth.
The tooth morphology of the taxon from the Cedar
Mountain Formation is surprisingly similar to that of the
large teiid Polyglyphanodon from the North Horn For-
mation (Gilmore, 1942). Like Polyglyphanodon, the
teeth are transversely expanded, constricted at the base,
and have a lingual and a labial apex connected by a crest.
Unlike Polyglyphanodon, however, the crest connecting
the apices forms a shallow "V" instead of a horizontal
ridge in anterior view. Also, OMNH 29771 has anterior
and posterior ridges that circumscribe shallow anterior
and posterior semicircles and border shallow basins on
either side of the central crest. Because of postdeposi-
tional abrasion these ridges are not completely preserved
on OMNH 32629. Although similar in shape to Poly-
glyphanodon, these specimens are from an animal much
smaller in size (see Gilmore, 1942, for an estimation of
the size of Polyglyphanodon).
The presence of a polyglyphanodontine lizard in the
Mussentuchit local fauna would represent the earliest
record for the group, which is otherwise restricted to the
Campanian and Maastrichtian of North America (Estes,
1983) and ?Campanian of Mongolia (Estes, 1983; Sulim-
ski, 1975). Unfortunately, the material on hand is not
nearly complete enough to support more than a tentative
assignment to the Polyglyphanodontinae (in the sense of
Estes, 1983). Materials currently under study indicate
that polyglyphanodontines may also occur in older Late
Cretaceous faunas (Turonian, southern Utah) than previ-
ously thought, suggesting that this group may have an
extensive North American temporal record (Nydam, this
volume).
Three specimens (OMNH 27381, 27388, and 27711)
from locality V695 are referred to Scincidae. These
specimens, possibly representing at least two taxa, do not
compare readily to known Cretaceous taxa and referral to
Scincidae is tentative. One of the specimens, OMNH
27711, is a broken right maxilla with low crowned teeth.
The general appearance of this specimen is similar to
that of Eumeces; however, this would extend the earliest
record of this genus from the Oligocene to the medial
Cretaceous, a doubtful prospect based on the current
record of Cretaceous scincids. The lack of material that
can be confidently assigned to Scincidae is not surprising
in view of the globally poor Mesozoic fossil record of
this group (Estes, 1983).
Not nearly as abundant as the teiid with bicuspid
posterior teeth, but also widespread in the formation, are
two species of scincomorph lizards tentatively referred to
the Paramacellodidae. These taxa are most common in
locality V868, but also are known from four other locali-
ties. Placement in the Scincomorpha is supported by the
well-developed, albeit small, subdental gutter and sub-
dental shelf as well as the thick cementum at the bases of
the teeth. The crowns of the teeth are striated lingually
and have an apex posterior to the midline of the shaft of
the tooth which is formed by an anterior cutting edge
that is longer than the posterior cutting edge. These two
cutting edges turn medially towards the apex and form a
posteromedially directed "v" in occlusal view. The teeth
are also slightly rotated posteriorly around their long
axes such that the anterior edges are exposed medially
and the posterior edges are exposed laterally. This tooth
morphology has been recognized as diagnostic of
Anguidae (Gauthier, 1982; Estes and others, 1988), but
has also been reported for taxa in the Scincidae (Gao and
Fox, 1996) and Paramacellodidae (Broschinski and
Sigogneau-Russell, 1996). The presence of a subdental
shelf and subdental gutter clearly indicate that the
Mussentuchit lizards are scincomorphan and thus elimi-
nate the possibility of anguid affinities. Broschinski and
Sigogneau-Russell (1996) describe the teeth of Parama-
cellodus as having a small, secondary apex (formed by
the distal junction of two of the lingual striae) which is
offset from the more labial, primary apex. These two
cusps are connected by a small, transverse carina. The
teeth of the Mussentuchit scincomorphs have a similar
construction and are therefore referred to the ?Parama-
cellodidae. The reference is tentative, however, pending
the resolution of relationships between Paramacellodidae
and Cordylidae (see Estes, 1983). The two species of the
Mussentuchit local fauna are distinguished primarily on
the basis of morphological differences in the teeth.
Species A is the best represented of the two; a complete
dentary (OMNH 33889) is known from locality V868.
The teeth of this species form a more acute apex in later-
al view, bear an offset anterior cutting edge, and have

230 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
weak labial striations on the crowns. The crown of
species B in lateral view is blunt and the lingual stria-
tions of the crown are well developed. Formal descrip-
tion of both taxa is presently underway by one of the
authors (RLN).
The possible existence of a helodermatid varanoid in
the Cedar Mountain Formation was first suggested by
Cifelli and Nydam (1995) in their description of a partial
maxilla with widely spaced, plicidentine teeth, and osteo-
derms fused to the exterior surface of the maxilla. Since
then, a partial dentary referable to the same taxon has
been recovered from the same locality (V695), and fur-
ther description and systematic work are in progress.
This adds to the lizard fauna a taxon that presumably
incorporated vertebrate prey in its diet, whereas the rest
of the lizards are interpreted as having been insectivo-
rous. The earliest published record of Helodermatidae is
generally considered to be that of Lancian Paraderma.
Assuming the material from the Cedar Mountain is cor-
rectly referred, it represents a significant increase in the
temporal range of this group and thus begins to fill the
gap between terrestrial and aquatic varanoids (see Carroll
and deBraga, 1992, for discussion of the fossil record of
these groups; see also Caldwell and others, 1995, for an
alternative hypothesis of relationships among advanced
anguimorphs).
In addition to the possible helodermatid, field work
has resulted in the recovery of a single osteoderm
(OMNH 28460) that is similar to those described for the
varanoid Necrosaurus (Fejéráry, 1918, 1935; Estes,
1983). The osteoderm is unornamented, elongate, and
strongly arched. Unlike similar osteoderms described for
Necrosaurus, this osteoderm is large and has smooth,
regular edges. The possibility that this osteoderm
belongs to the aforementioned ?helodermatid is unlikely
due to the lack of similar ornamentation on the fused
osteoderms of the maxilla of that taxon. Placement in
Crocodilia is also dismissed for the lack of the character-
istic pit and ridge sculpturing common to that group.
Because of the lack of additional, more diagnostic mate-
rials, a taxonomic assignment for the osteoderm is with-
held at this time, although it can be tentatively consid-
ered to be indicative of a necrosaurian-grade varanoid.
As with most of the taxa of the Mussentuchit local
fauna, the lizards described herein are more characteris-
tic of described Late Cretaceous than Early Cretaceous
faunas (see citations above). This is interesting because
the Mussentuchit local fauna is not substantially younger
than the more primitive assemblage described from the
Trinity Group of Texas (Winkler and others, 1990).
Investigations are underway to determine the extent to
which the evolution of angiosperms may have con-
tributed to the apparent rapid change in lizard faunas
(Nydam, work in progress). It should also be stressed
that faunal comparisons are, perforce, based on a very
limited fossil record.
Two snake vertebrae, OMNH 33250 and 33251,
from OMNH V695 and V867, respectively, are referable
to the primitive, anilioid-grade alethinophidian Conio-
phis. This genus previously was known from the Cam-
panian to Eocene of North America, South America, and
Europe (for example, Rage, 1984, 1987, 1988; Albino,
1996). OMNH 33250 and 33251 are of paleobiogeo-
graphic interest, because they are among the geologically
oldest snake fossils known from anywhere in the world
and they represent the oldest occurrence of snakes in the
New World by at least 10 Ma (Gardner and Cifelli,
1999).
Crocodilia
At least seven taxa of crocodilians are represented in
the Mussentuchit local fauna; most of these are known
only by incredibly abundant, isolated teeth, but several
skulls and some articulated postcranial materials are
known: much of this is not yet prepared, and none of it
has been studied; hence, the provisional identifications
presented herein are based solely on the dentition.
Bernissartia, best known from the Early Cretaceous of
Europe (for example, Buffetaut and Ford, 1979), has also
been reported from the Aptian-Albian of Texas (Winkler
and others, 1990); apparently, however, Bernissartia-like
crocodilians with a durophagous dentition are widely dis-
tributed in the Cretaceous of the southern Western Interi-
or, ranging through the Dakota, Straight Cliffs, and Wah-
weap Formations in southern Utah (Eaton and others,
this volume). Probable first occurrences in the Mussen-
tuchit local fauna include the goniopholidids cf. Dakota-
suchus and Polydectes; the record of the teleosaurid
Machimosaurus (based on rare but very distinctive teeth)
is a probable last occurrence.
Dinosauria
A diverse array of Theropoda is present in the fauna;
at least six taxa, most of which are small coelurosaurs,
are known. Each theropod taxon is represented by iso-
lated teeth; in addition, isolated postcranials are known
for several taxa, and a partial associated skeleton is
known for one of the dromaeosaurids. Among
coelurosaurs, the records of Dromaeosaurinae, Troodon-
tidae, cf. Paronychodon, and cf. Richardoestesia repre-
sent first occurrences. Most noteworthy among
theropods is a tyrannosaurid similar to Alectrosaurus,
otherwise known from the Late Cretaceous of Asia
(Gilmore, 1933); this family is first recorded from the

Miscellaneous Publication 99-1 231Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Early Cretaceous of southeast Asia (Buffetaut and others,
1996).
A ?brachiosaurid sauropod is represented by small
teeth (less than 1 cm in crown length) morphologically
indistinguishable from those of Astrodon (see summaries
by Lull, 1911; Gilmore, 1921; Ostrom, 1970; Langston,
1974). Astrodon (and its probable synonym, Pleuro-
coelus) is a broadly distributed but generally rare taxon
in the Early Cretaceous of North America, and is known
from the Arundel Formation, Trinity Group, Cloverly
Formation, and the lower part of the "shale" member of
the Cedar Mountain Formation. The taxon in the
Mussentuchit local fauna apparently represents the last
North American record of Sauropoda, prior to their brief
reappearance (in the form of the titanosaurid Alamo-
saurus) in Maastrichtian rocks of the Southwest -- pre-
sumably through immigration from South America (see
Lehman, 1987; Lucas and Hunt, 1989). Interestingly, all
known specimens of the sauropod from the upper Cedar
Mountain Formation are from extremely small individu-
als: either some sampling bias has favored the represen-
tation of juveniles alone, or the taxon itself was remark-
ably small, by sauropod standards. Given the intense
sampling (including use of both microvertebrate and
macrovertebrate recovery techniques) and the abundance
of localities in the upper part of the Cedar Mountain For-
mation, with representation of several different deposi-
tional (and presumably paleoenvironmental) settings, we
consider this second interpretation to be at least viable, if
not favorable.
The most abundant dinosaur -- and for that matter,
the most abundant vertebrate represented by anything
other than isolated teeth -- from the Mussentuchit local
fauna is a hadrosaurid (Kirkland, 1994), represented by
several incomplete skeletons, cranial material, jaws, and
innumerable isolated teeth. This probable new genus is
the oldest member of the family. The majority of speci-
mens represent small, immature individuals, suggesting
high mortality rates for younger members of the species,
frequenting of the area by this taxon during time inter-
vals corresponding to certain early, ontogenetic growth
stages, or some other unknown factor(s). Three small,
hypsilophodontid ornithopods are also present in the
fauna; of these, one is similar to Zephyrosaurus, other-
wise known from the Cloverly Formation of Montana
(Sues, 1980). The Mussentuchit local fauna includes a
nodosaurid (based on teeth) similar to Pawpawsaurus,
which was described from upper Albian rocks of Texas
(Lee, 1996). Marginocephalia are represented by a neo-
ceratopsian and a pachycephalosaur, both tentatively rec-
ognized on the basis of isolated teeth. Assuming correct
identification, the latter is of interest in representing the
first North American appearance of the group; the oldest
pachycephalosaur, Yaverlandia, is from the Barremian of
the Isle of Wight (Galton, 1971). The neoceratopsian
also deserves comment because of its geologic age: only
two, somewhat ambiguous occurrences may antedate it;
one includes skeletal material from the Albian Wayan
Formation, Idaho (Weishampel, 1990), the other is based
on an enigmatic tooth recently collected from the Arun-
del Formation, Maryland (Kranz, 1996), of similar age.
At least two dental morphs of Avialae are present in
the fauna; one of these appears referable to the Hesperor-
nithiformes. These teeth have bulbous bases and rare
serrations; they compare closely with hesperornithiform
teeth from the Dinosaur Park Formation, Canada (Kirk-
land, unpublished data). The great abundance of these
teeth (which superficially look like hypsilophodont pre-
maxillary teeth) supports their tentative allocation to
Hesperornithiformes as the most parsimonious identifica-
tion. The earliest record of this group of toothed diving
birds is generally considered to be Enaliornis, from the
Early Cretaceous of England (for example, Unwin, 1993;
Feduccia, 1996); the genus is also tentatively recorded
from the Cenomanian Greenhorn Formation, Kansas.
Additional hesperornithiform birds are known from
marine units spanning the Turonian through Campanian
of North America. If the teeth from the Cedar Mountain
Formation are correctly identified, they represent only
the second occurrence in nonmarine rocks on the conti-
nent -- the other being a report of Hesperornis in the
Campanian of Canada (Fox, 1974). In Asia, Hesperor-
nithiformes appear somewhat later, and are known from
the Santonian through ?Maastrichtian; some of the Asian
occurrences are also from nonmarine units (Kurochkin,
1995).
Remains of fossil eggs have long been known from
the upper part of the Cedar Mountain Formation, but
their identification is uncertain (for example, Jensen,
1970). Hirsch (written communication, 1996) examined
material from a number of the OMNH localities and
reported that all eggs are of the dinosauroid-spherulitic
type, with protolaterospherulitic and angustiprismatic
morphotypes being most common (see Hirsch and
Quinn, 1990 for explanation of terminology and classifi-
cation schemes). These types are found among
Ornithopoda; the protolaterospherulitic structural mor-
photype is known for Hadrosauridae. Though a taxo-
nomic referral of eggshell materials from the upper
Cedar Mountain Formation cannot be made at this time,
these data suggest that some, at least, may belong to the
extremely abundant hadrosaurid known from the
Mussentuchit local fauna. There is also the suggestion of
a distinct pattern to the geographic distribution of egg-

232 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
shell within the upper part of the Cedar Mountain For-
mation. Although isolated eggshell fragments can be
found practically wherever this part of the unit is
exposed, extremely dense, largely monotypic concentra-
tions (suggesting proximity to a colonial nesting site)
seem to be limited to the western side of the San Rafael
Swell. Sites have been noted as far north as Castle Dale
(Jensen, 1970) and Ferron (Fiorillo, this volume), Emery
County, but denser spacing of sites occurs south of this,
from OMNH locality V239 to near locality V868. This
apparent distribution may reflect sampling bias, sedimen-
tological or depositional factors, or, perhaps, preferential
selection of nesting sites. Further investigation is clearly
warranted.
Mammalia: Multituberculata
The sample of multituberculate specimens on which
Eaton and Nelson (1991) based their systematic discus-
sion was relatively small and from localities all within
the upper few meters of the formation. Collections made
subsequently by Cifelli and currently under study by
Eaton are much larger and appear to include at least
eight multituberculate taxa. These new collections will
vastly improve our knowledge of the Early Cretaceous
evolution of multituberculates in the Western Interior.
This report represents the results of a cursory examina-
tion of the OMNH material (by Eaton) and is based
largely on first molars.
Eaton and Nelson (1991) described as incertae sedis
a single, peculiar m1 (FHSM 10350; figure 1A) that has
very broad, U-shaped valleys between the cusps in the
same row. The new OMNH material includes more
specimens of this morphologic style, including some
extremely strange molar forms unlike any published mul-
tituberculates of any age. These peculiar teeth may rep-
resent a previously unrecognized clade of multitubercu-
lates, perhaps distinct at the level of suborder.
Virtually all of the remaining specimens are at a
“Paracimexomys” grade of evolution in that cusp counts
are low, cusps are primarily pyramidal to sub-pyramidal
(not crescentic) in occlusal view, and the internal cusp
row on M1s is poorly developed. Current diagnoses
would place most of these specimens within the genus
Paracimexomys. However, the concept of this taxon is
based largely on primitive characteristics expressed in a
Maastrichtian form on which the type of the genus is
based (Archibald, 1982). There is a vast range of subtle
morphologic variation within these specimens that will
take time to analyze and interpret. This subtle morpho-
logic variation may mark the initial divergence from a
Paracimexomys-like ancestor that possibly (but not
demonstrably) gave rise to many later Cretaceous multi-
tuberculate taxa.
The OMNH sample includes a variety of species (as
many as six, including those referred to the genus with
doubt) of Paracimexomys, including at least one species
distinctly smaller than Paracimexomys robisoni (Eaton
and Nelson, 1991, table 1). Specimens of this small
taxon are similar in size to what Eaton and Nelson
(1991) described as ?Paracimexomys n. sp. B. However,
the latter taxon does not have the cusp arrangement char-
acteristic of other species of Paracimexomys (alternation
of cusp position between the internal and external cusp
rows). This suggests that these two small taxa from the
Mussentuchit local fauna will probably be found to
belong in different genera when study and analysis is
completed.
Eaton and Nelson (1991) described a large taxon as
Paracimexomys bestia based on an m1, two p4s, and an
m2. Many large M1s in the OMNH sample are morpho-
logically what might be expected in this taxon. These
M1s are primitive in having either no internal cusp row
or only a single, labially appressed cusp on the lingual
side of the tooth; however, they are smaller than would
be expected for M1s of P. bestia. The m1 of P. bestia
(AP=2.7; LB=1.7, Eaton and Nelson, 1991, table 1) is
larger than these upper molars (mean AP=2.4; mean
LB=1.4), whereas the reverse is generally true of multi-
tuberculates. This suggests the presence of a taxon
smaller than, but similar to, P. bestia. The primitive
nature of the M1s (cusp formula 3:4:1-0) and strong
anterior divergence of the cup rows raises question about
the placement of P. bestia within Paracimexomys, and
that assignment is questioned in the revised faunal list
presented here (table 1).
Also of interest in the large OMNH sample are M1s
that have a distinct internal cusp row bearing at least two
cusps that connect to the posterior part of the second
cusp of the medial row (which has four cusps). The
overall cusp formula of the M1s is low (3:4:2), as in
Paracimexomys. The M1s are approximately the same
size as those of Paracimexomys robisoni (Eaton and Nel-
son, 1991, table 1), but the internal cusp row is much
better developed than in described specimens of
Paracimexomys. The internal cusp row is about half the
length of the tooth, a condition similar to that found in
Cimexomys (for example, Archibald, 1982), but these
M1s are otherwise quite unlike the latter in cusp shape
and position. These specimens also have deep pits in the
valleys between cusp rows and cusps are coarsely ribbed
at their bases. This suggests a taxon is present in the
Cedar Mountain Formation that is distinct from
Paracimexomys and all other known multituberculate
genera.

Miscellaneous Publication 99-1 233Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Multituberculates from the Cedar Mountain Forma-
tion represent part of the transition from Late Jurassic to
Late Cretaceous forms, and the analysis of this fauna is
critical to understanding the relationships of all later
multituberculates. With the possible exception of the
morphologically divergent taxon mentioned above, all
taxa appear to be referable to Ptilodontoidea
(Cimolodonta of Simmons, 1993), which are prevalent in
North American faunas of the Late Cretaceous and early
Tertiary.
Mammalia: Triconodonta, Symmetrodonta, and
Tribosphenida
Triconodonta: Triconodonts, most characteristic of Juras-
sic faunas (see Simpson, 1928, 1929; Jenkins and
Crompton, 1979), are rare elements of North American
Cretaceous assemblages: until recently, one species each
had been described from the Trinity Group, Texas (Pat-
terson, 1951; Slaughter, 1969); the upper Milk River For-
mation, Alberta (Fox, 1969, 1976); and the Cloverly For-
mation, Montana (Jenkins and Schaff, 1988). In this
context, the presence of three species of Triconodontidae
in the Mussentuchit local fauna appears somewhat sur-
prising. Although triconodonts clearly were minor ele-
ments of North American Late Cretaceous faunas (only
one species, represented by only two specimens, is
known; Fox, 1969, 1976), low diversity in the Early and
medial Cretaceous may simply reflect a sampling bias:
recent work suggests the presence of as many as four
species of triconodonts in the Cloverly Formation
(Cifelli, Wible, and Jenkins, 1998). North American
Cretaceous triconodontids appear to form a monophyletic
clade with respect to the remainder of the family; the
three species from the Mussentuchit local fauna are
placed in separate genera (Cifelli and Madsen, 1998).
The smallest species appears to be referable to the
Aptian-Albian genus Astroconodon; another is congen-
eric with a species belonging to a genus being described
from the Aptian-Albian Cloverly Formation (Cifelli,
Wible, and Jenkins, 1998). The remaining species is
astonishingly large (approximately equivalent in size to
Gobiconodon from the Cloverly Formation; Jenkins and
Schaff, 1988), by the standards of Mesozoic mammals,
and is placed in a new, monotypic genus. The large size
and presumed predaceous habits of this last species sug-
gest that, as with the varanoid squamate noted above, it
probably incorporated vertebrate prey in its diet.
Symmetrodonta: By the Cretaceous, symmetrodonts were
also archaic, relictual taxa (for example, see Cassiliano
and Clemens, 1979). In North America, most known
taxa are referred to the Spalacotheriidae, with one
species each being known from the following units:
lower Campanian Wahweap Formation (Cifelli and Mad-
sen, 1986), Utah; the upper Milk River Formation (Fox,
1976), Alberta; Aptian-Albian Trinity Group (Patterson,
1956), Texas; Aptian-Albian Cloverly Formation,
Wyoming (Cifelli, unpublished data); and Santonian
John Henry Member, Straight Cliffs Formation, Utah
(Eaton, 1991; Eaton and others, this volume). Two
species are known from the Turonian Smoky Hollow
Member, Straight Cliffs Formation, Utah (Cifelli, 1990;
Eaton and others, this volume). Three species, all Spala-
cotheriidae, are present in the Mussentuchit local fauna:
one is tentatively referred to Symmetrodontoides (a first
occurrence of a genus that is otherwise known from the
Turonian through early Campanian of Utah and the Cam-
panian of Alberta), and a second is referable to Spala-
cotheridium (also a first occurrence; the only other
record of the genus is from the Turonian of Utah). The
third species of spalacotheriid is large by symmetrodont
standards and may be referable to a new genus (Cifelli
and Madsen, unpublished data). Small teeth of very
primitive aspect, resembling those of both triconodonts
and tinodontid or kuehneotheriid symmetrodonts (see
Fox, 1984), are rather abundant at several sites, and are
present in one jaw from OMNH V695. It is possible that
these small teeth represent deciduous premolars of spala-
cotheriid symmetrodonts (similar teeth, though rare in
occurrence, also are know from almost all other sites
which have produced adult remains of spalacotheriids in
North America; they are lacking from sites which have
not yielded specimens of adult symmetrodonts). The
abundance of these specimens suggests high juvenile
mortality, delayed replacement of deciduous premolars
by permanent teeth, or other, unknown factors in one or
more species of Spalacotheriidae from the Mussentuchit
local fauna.
Tribosphenida: Tribosphenic mammals of the Mussentu-
chit local fauna have not yet received detailed study.
The only taxon published thus far is Kokopellia juddi, a
marsupial-like mammal known from reasonably good
material (Cifelli, 1993a). This species is probably the
most abundant tribosphenic mammal in the upper part of
the Cedar Mountain Formation, and new materials show
that four lower incisors (perhaps the primitive count for
Tribosphenida; Clemens and Lillegraven, 1986) were
present. Two taxa present in the fauna appear to be bona
fide marsupials, judged by the tight apposition of
hypoconulid to metaconid on lower molars (see
Clemens, 1979). As many as four other tribosphenic
mammals of the Mussentuchit local fauna cannot be con-
fidently allied with either Eutheria or Marsupialia, and
fall into the awkwardly named category, "therians of
metatherian-eutherian grade" (Patterson, 1956; see

234 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
reviews by Kielan-Jaworowska and others, 1979; Cifelli,
1993b). One (see Nelson and Crooks, 1987, figure 8A)
is similar to the aberrant Picopsis, first described from
the lower Campanian Milk River Formation, Alberta
(Fox, 1980), but with possible relatives known from the
Turonian Smoky Hollow Member, Straight Cliffs Forma-
tion, Utah, and, perhaps, the Maastrichtian Lance Forma-
tion, Wyoming (Cifelli, 1990). If these poorly known
taxa represent a divergent but phylogenetically related
group of tribosphenic mammals, the Mussentichit local
fauna represents the first appearance of this clade.
Two other tribosphenic mammals are similar in gen-
eral appearance to Pappotheriidae, known from the
Lower Cretaceous of Texas and Oklahoma (Butler, 1978;
Cifelli, 1997). A final therian of metatherian-eutherian
grade from the Mussentuchit local fauna is a large taxon
with somewhat bulbous, inflated molars; morphological-
ly, it is vaguely reminiscent of Dakotadens, from the
Dakota Formation of southern Utah (Eaton, 1993; Eaton
and others, this volume).
DISCUSSION AND CONCLUSIONS
As noted previously (Cifelli, Kirkland, and others,
1997), the fauna from the upper part of the "shale" mem-
ber, Cedar Mountain Formation, is rather different from
other known assemblages, with only about one-third of
the genera surely being known from elsewhere -- a result
that is predictable in view of the fact that the Mussentu-
chit local fauna lies within an otherwise poorly known
time interval. Also unsurprisingly, almost half of the
taxa represent stratigraphic range extensions. The major-
ity of these are for taxa or groups otherwise known from
the Late Cretaceous, indicating that the Mussentuchit
local fauna resembles assemblages of that epoch more
closely than it does those of the Early Cretaceous or
older intervals. Most noteworthy of last appearances is
that of the small ?brachiosaurid recorded in the fauna.
Negative evidence must always be interpreted with cau-
tion, and dinosaur faunas of slightly younger age in
North America are poorly known (see, for example, sum-
mary by Eaton and others, this volume). Nonetheless, it
is clear that a significant "sauropod hiatus" (Lucas and
Hunt, 1989) separates this occurrence from the ephemer-
al presence of the titanosaurid Alamosaurus in the latter
half of the Maastrichtian of North America (Lehman,
1987). The limited evidence now available suggests that
the little (possibly dwarfed) sauropod from Mussentuchit
approximates the North American upper stratigraphic
limit for this group of usually enormous dinosaurs that
dominated the continent's faunas in the Upper Jurassic.
A brachiosaurid said to be of similar age has recently
been reported from Arizona (McCord and Tegowski,
1996).
First North American or global appearances include
three chondrichthyans, scapherpetontid salamanders, two
lizards (including a possible relative of Helodermatidae),
Serpentes, five taxa of theropods, several ornithopods,
and several taxa of mammals. Of these, the most notable
is Hadrosauridae, a group that was to become remark-
ably diverse and well-represented in Late Cretaceous
faunas of North America (for example, Weishampel and
Horner, 1990). Well-known earlier assemblages, such as
those of the Cloverly Formation and the Trinity Group,
are dominated by the basal iguanodontian Tenon-
tosaurus (for example, Ostrom, 1970; D. L. Brinkman,
oral communication, 1997) which, like hadrosaurs, was
probably a low-level browser and possessed a sophisti-
cated masticatory apparatus (for example, Weishampel,
1984) -- hence the paleobiological significance of this
replacement among herbivores is unclear. Diversity of
extremely large-bodied herbivores is rather low in the
Mussentuchit local fauna, as it generally is in other mid-
Cretaceous assemblages -- a situation quite different
from what is encountered in the Late Jurassic and Late
Cretaceous (Wing and Tiffney, 1987; Cifelli, Kirkland,
and others, 1997).
Temporal distribution, phylogenetic relationships, or
both are suggestive of an Asian origin for a number of
the taxa appearing in the Mussentuchit local fauna, an
hypothesis that is consistent with existing data based on
plate tectonics and marine invertebrates (Cifelli, Kirk-
land, and others, 1997). Taxa with a possible Asian ori-
gin include scapherpetontid salamanders and a number of
the dinosaurs, including Troodontidae, Tyrannosauridae,
Hadrosauridae, and (depending on the veracity of report-
ed Early Cretaceous occurrences in North America) Neo-
ceratopsia. The myliobatiform cf. Baibisha first appears
in North America: it is possible that it immigrated to
Asia (as may also be the case for Hesperornithiformes,
which also appear earlier in North America than they do
in Asia). Other taxa in the Mussentuchit local fauna are
represented by older relatives or proximate sister taxa in
Europe or Africa (Coniophis, Pachycephalosauria, Hes-
perornithiformes), highlighting the complexity of global
biogeography in the Cretaceous.
ACKNOWLEDGMENTS
We are most grateful to Michael Nelson for his gen-
erosity in making his localities and fossils available to us
for study, and to D. L. Brinkman and D. A. Winkler for

Miscellaneous Publication 99-1 235Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
providing helpful review comments on an earlier version
of the manuscript. Our thanks go also to the Judd family
of Castle Dale, Utah, for their unwavering help with so
many aspects of field work; to E. M. Larson, E. Miller,
K. S. Smith, and other individuals too numerous to men-
tion for help in the field and lab; and to Tom Rasmussen
for the continuing cooperation of the U.S. BLM. For
access to specimens we thank J. Bolt and W. F. Simpson
(Field Museum of Natural History). JIK is grateful to D.
Burge (College of Eastern Utah Prehistoric Museum) and
R. and C. Jones for cooperation in field activities. Fig-
ure 1 was drafted by Coral McCallister, and K. S. Smith
supplied the photographs reproduced herein. Partial
funding for support of this research was provided by the
National Geographic Society (grants 4761-91 and 5021-
92 to RLC; 5263-94 to JIK) and the National Science
Foundation (grants BSR 8906992 and DEB 9401094 to
RLC); RLN acknowledges financial support from Sigma
Xi, the American Federation of Mineralogical Societies,
the Graduate Student Senate of the University of Okla-
homa, and the Department of Zoology of the University
of Oklahoma. JDG's part in this study has been support-
ed by a Field Museum of Natural History Visiting Schol-
ar Grant, a University of Alberta Ph.D. Dissertation Fel-
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194.

Miscellaneous Publication 99-1 239Vertebrate Paleontology in Utah
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APPENDIX: MEASURED SECTIONS
The three measured sections described below all lie in the immediate area of Mussentuchit Wash; see figure 1 for approximate locations and
figure 2 for graphic depiction of sections. Classification of pedogenic calcretes and caliches is based on Retallack's (1988, p. 16) "Stages of car-
bonate accumulation in paleosols." Color descriptions are subjective.
The Cedar Mountain Formation in this area was deposited in three distinct environmental regimes: the first is the fluvial depositional environ-
ment that produced the basal Buckhorn Conglomerate (unit 1 in Section A, units 1 and 2 in Section B, and unit 1 in Section C). Above the Buck-
horn Conglomerate, however, the prevalence of carbonate nodules and cemented carbonate horizons suggests that paleosols formed in a semi-arid
environment make up the lower part of the Cedar Mountain Formation (units 2-18 in Section A, units 3-7 in Section B, and units 2-4 in Section C).
In contrast, the presence of sand lenses, channel sands, carbonaceous shale and apparently floodplain-derived fossil deposits in the upper part of the
formation, which completely lacks carbonate nodules, indicates a substantial environmental shift toward a wetter, more fluvially influenced deposi-
tional regime.
Section A: (Measured on S-facing slope; includes OMNH localities V235, 694, 695, 794)
Unit Section Height Description Thickness
31 56-57 m Siltstone, sandy, rapidly grading to resistant, 1.0 m
medium-grained sandstone of the Dakota Formation.
30 55-56 m Mudstone, clayey, light grey, small sand channels. 1.0 m
Sandstone fine to medium grain size with some large
mud rip-up clasts, chunks of carbonized wood.
29 54.5-55 m Carbonaceous shale, plant hash, mud stringers, 0.5 m
some sulfur and secondary gypsum present, weathers
brown to purple.
28 53.4-54.5 m Siltstone, grey, very sandy. 1.1 m
27 52.8-53.4 m Sandstone, fine grained, grey. 0.6 m
26 43.3-52.8 m Mudstone, light grey to greenish grey, weathered 9.5 m
more than a meter into the slope in places. At about
47 m some iron staining, mudstone darker.
25 43-43.3 m Sandy siltstone to fine sandstone, plant hash and 0.3 m
carbonized wood common, mud clasts about 1 cm
in diameter near the top of the interval.
24 41.7-43 m Siltstone, light grey, with some very thin, discon- 1.3 m
tinuous, non-resistant sandstone.
23 41-41.7 m Level of OMNH localities V235, V240, V794. This 0.7 m
horizon is variably fossiliferous along the outcrop.
V235 was not exposed, so thickness of the productive
layer was not measured. The productive layer at V240
and V794 is 60-70 cm thick, grey, silty, with plant de-
bris, small bone fragments, and teeth.
22 37.73-41 m Siltstone, light grey, with very thin, discontinuous, 3.27 m
non-resistant sandstone.
21 37.7-37.73 m Ash, occurs above bone at OMNH V695. 0.03 m
20 37-37.7 m Siltstone, light grey, with very thin, discontinuous, 0.7 m
non-resistant sandstone.
19 36.2-37 m Sandstone, fine grained, color grey weathering brown 0.8 m
to brownish red, thickness variable 30-70 cm. Variably
resistant, a channel sand with low-angle tabular cross-
bedding, continuous across the outcrop, holds up a slope
break between light grey and dark grey mudstone, with
mud weathered over it in places. 36.7 m: OMNH V695
quarry bottom.
18 28.6-36.2 m Mudstone, grey with dark brown veining at about 7.6 m
32.5 m, no nodules, smooth pebbles of up to 1 cm
diameter size on surface, but none found in place.
17 28.5-28.6 m Mudstone, with yellow round and ovoid carbonate 0.1 m
nodules of golfball to baseball size and stained
yellow (Stage II carbonate accumulation).

240 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
Unit Section Height Description Thickness
16 25.8- 28.5 m Mudstone, grey and greenish grey with orange 2.7 m
staining, varying silt content, no nodules, no bedding.
15 23.75-25.8 m Mudstone with scattered carbonate nodules 3.0 m
(Stage II carbonate accumulation).
14 23.75 m Calcrete: a layer of large ovoid nodules, with cement 0.05 m
in some places forming a continuous horizon
(Stage III carbonate accumulation).
13 13.2-23.75 m Mudstone, greenish grey and grey weathering to light 10.55 m
grey. Caliche nodules (Stage II carbonate accumulation)
of varying shapes, sizes, and colors throughout the in-
terval: at 13.2 m a layer with ovoid nodules of yellow
color measuring about 14 cm x 10 cm x 3 cm. Above
this nodules are smaller and scattered. At 14.5 m nodules
are similarly large and ovoid, weathering to reddish brown
or yellowish brown where exposed. Between 14.5 m and
about 18 m nodules are scattered, round or ovoid, 5-10 cm
in diameter, and mixed with rounded smooth pebbles.
Fewer nodules occur in the 18-18.5 m interval. They are
again very numerous at 18.5 m, but decrease in size to-
ward the top of the interval.
12 9-13.2 m Mudstone, light grey with limonitic staining. Slopes covered 4.1 m
with fragmentary nodules, probably from upsection.
11 9 m Mudstone, including a layer of caliche nodules that are round 0.1 m
and up to 10 cm in diameter (Stage II carbonate accumulation).
10 7.65-9 m Mudstone, color grey-green. 1.35 m
9 7.5-7.65 m Calcrete: Stage IV carbonate accumulation, hard, resistant, 0.15 m
white, weathering into nodules. Appears to be a sandstone
from a distance.
8 5.6-7.5 m Mudstone, becoming more greenish in color higher in the interval. 1.9 m
Abundant caliche: nodules small pebble-sized at the base, increasing
to golf ball size. At 7 m there is a thin horizon in which carbonate
cements the silt and mudstone (Stage III carbonate accumulation).
Above this horizon there is more mudstone with large nodules.
7 5.4-5.6 m Sandstone, fine to medium grained, buff color weathering to reddish 0.2 m
brown, variable thickness and probably discontinuous, erosive base.
6 3.85-5.4 m Mudstone. 1.55
5 3.75-3.85 m Sandstone, fine grained with hard carbonate cement, not resistant. 0.1 m
4 2.6-3.75 m Fine siltstone or mudstone, deeply weathered, buff color. 1.15 m
3 2.5-2.6 m Sandstone, medium grainsize, thin and discontinuous, grey color, 0.1 m
flaky weathering, trough cross-beds.
2 1.1-2.5 m Siltstone, heavily weathered. 1.4 m
1 0-1.1 m Sandstone, fine to medium grain size, thickness variable to max- 1.1 m
imum of approximately 3 m, grey color weathering buff, channels
with cross-beds. Resistant, forming ledges between surrounding silts.
Section B (Measured through OMNH V824)
Unit Section Height Description Thickness
16 31 m Base of resistant, medium-grained sandstone, typical of the Dakota
Formation.
15 29.2-31 m Section covered by slabs of Dakota Formation sandstone that have 1.8 m
come down as surface float.
14 28-29.2 m Mudstone, light grey. 1.2 m

Miscellaneous Publication 99-1 241Vertebrate Paleontology in Utah
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Unit Section Height Description Thickness
13 27.2-28 m Carbonaceous shale with abundant plant hash, in places 0.8 m
verging on impure lignite with some sub-bituminous seams.
Secondary gypsum present. Dark brown color, weathers out
light brown.
12 21.3-27.2 m Mudstone, grey with some patches of iron staining, lenses 5.9 m
of fine grey sand, cross-bedded, weathering out grey and flaky.
OMNH V824 at 23 m.
11 20.9-21.3 m Sandstone, thickness variable to maximum 40 cm. A long lens, 0.4 m
extending about 200 feet N-S. Fine- to medium grained sand,
resistant and highly visible, grey weathering to reddish brown.
10 18.2-20.9 m Mudstone, light grey, sharp contact with underlying conglomerate. 2.7 m
9 17.5-18.2 m Mudstone, coarsens upward over 50 cm to a microconglomerate at 0.7 m
18 m. Microconglomerate dark brown, discontinuous, contains silt,
fine sand, mud clasts, tiny pebbles, plant fragments, and rare stream-
worn bone.
8 11.7-17.5 m Mudstone, light grey. Smooth pebbles range in size up to 2 cm 5.8 m
diameter, occur first in surface float at about 14 m, are sparsely and
randomly distributed in the mudstone between about 15-16 m.
7 11.5-11.7 m Siltstone, very light grey, hard carbonate cement, holds up slope 0.2 m
break, weathers out nodular.
6 8-11.5 m Mudstone, light greenish grey, small caliche nodules sparse up to 3.5 m
10 m and absent above.
5 6-8 m Mudstone, light greenish grey, fining upward within the interval. 2.0 m
Caliche nodules between 6-7 m numerous and small, and then in-
crease in size within interval (Stage II carbonate accumulation).
4 5.9-6 m Siltstone or fine sandstone, carbonate cement with no visible crystal- 0.1 m
line structure, lighter color than surrounding mudstone, hard but not
resistant, tiny organic fragments present.
3 3-5.9 m Mudstone, light grey, variable sand content. At 4 m some lenses of 2.9
fine sand with carbonate cement, no identifiable sedimentary structures.
Fines upward slightly within the interval, secondary gypsum occurring
above 5 m.
2 2-3 m Sandstone, medium grain size, trough cross-bedded, not resistant. 1.0 m
1 0-2 m Conglomerate, holds up a wide bench over an unstable cliff of Morri- 2.0 m
son Formation muds, thickness highly variable, trough cross-bedding,
weathers reddish.
Section C
Unit Section Height Description Thickness
17 27.5 m Base of resistant, medium-grained sandstone typical of the Dakota
Formation.
16 21.75-27.5 m Section covered by slabs of the Dakota Formation sandstone that 5.75 m
have come down as surface float.
15 14-21.75 m Mudstone, light to dark grey, substantial secondary gypsum. 7.75 m
14 13.4-14 m Mudstone, light grey, fragmentary dinosaur bone. 0.6 m
13 13-13.4 m Ash, white, porous, weathered near the surface, discontinuous over 0.4 m
distance of less than 2 m.
12 12.9-13 m Mudstone, grey. 0.1 m

242 Utah Geological Survey
Medial Cretaceous Vertebrates - Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen
Vertebrate Paleontology in Utah
Unit Section Height Description Thickness
11 12.8-12.9 m Sandstone, light tan weathering to reddish brown; black to dark grey, 0.1 m
mostly fragmentary dinosaur bone weathering out (OMNH V826).
10 12.5-12.8 m Mudstone, light grey. 0.3 m
9 11.5-12.5 m Sandstone, thickness variable to maximum of 2 m, laterally 1.0 m
discontinuous.
8 10.28-11.5 m Mudstone, light grey. 1.25 m
7 10.25-10.28 m Conglomerate, identical to that described for the interval 8.75- 8.77. 0.03 m
6 8.77-10.25 m Mudstone, light greenish-grey. 1.48 m
5 8.75-8.77 m Conglomerate, 2-5 cm thick, clasts small pebble size, few of cobble 0.02 m
size, no visible cross-bedding, laterally continuous for at least 30 m,
not resistant, source of many pebbles in surface float downslope.
4 7.3-8.75 m Mudstone, light greenish-grey. 1.45 m
3 6.5-7.3 m Mudstone, light grey; at 7 m and again at 7.3 m large ovoid caliche 0.8 m
nodules greater than 15 cm length, distributed on apparently horizon-
tal surfaces (Stage II carbonate accumulation).
2 1-6.5 m Mudstone, light grey to greenish grey, occasional ovoid streamworn 5.5 m
rocks up to 8 cm length, lenses of fine sandstone in the lower part of
the interval, no other visible sedimentary structures.
1 0-1 m Conglomerate, clasts of coarse sand size to up to 5 cm diameter, trough 1.0 m
cross-bedding, weathers reddish, highly variable in thickness but thin-
ning to the E; to the W it holds up a steep slope of the underlying Mor-
rison Formation, and its dip slope forms the floor of a small valley.