Distribution of vertebrate faunas in the Cedar Mountain Formation, east -central Utah

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ABSTRACT
The Cedar Mountain Formation in east-central Utah
preserves three distinct dinosaur-dominated vertebrate
faunas in strata separated by unconformities. The oldest
fauna is preserved in the basal Yellow Cat Member of
the Cedar Mountain Formation in the area east of the San
Rafael Swell and includes an abundant new genus of
polacanthid ankylosaur related to Polacanthus, Iguan-
odon ottingeri, a sail-backed iguanodontid, a cama-
rasaurid and titanosaurid sauropods, a new genus of
theropod similar to Ornitholestes, and the giant dro-
maeosaurid Utahraptor ostrommaysorum. The polacan-
thid, iguanodontids, and titanosaurid indicate close tem-
poral geographic ties to the Barremian of Europe, where
similar dinosaurs occur. The Poison Strip Sandstone and
Ruby Ranch Member preserve a fauna including the
nodosaurid Sauropelta, the primitive iguanodontid
Tenontosaurus?, sauropods assigned to Pleurocoelus,
dromaeosaurid teeth, an unidentified large theropod, and
Acrocanthosaurus. This fauna compares well with those
documented from the Cloverly Formation, Arundel For-
mation, and Trinity Group characteristic of North Ameri-
ca’s apparently endemic Aptian-Albian dinosaur fauna.
A sharp break from carbonate-nodule-bearing, non-smec-
titic strata to carbonaceous, highly smectitic strata marks
the base of the Mussentuchit Member in the western San
Rafael Swell region. This member is dated as straddling
the Albian/Cenomanian boundary on palynological and
radiometric age estimates. The preserved fauna includes
a small nodosaurid Animantarx ramaljonesi, a small
ornithopod, a primitive lambeosaurid hadrosaur, ceratop-
sian teeth, pachycephalosaur teeth, tiny sauropod teeth, a
dromaeosaurid, cf. Richardoestesia teeth, cf. Parony-
chodon teeth, and an early tyrannosaurid. This fauna is
remarkably similar to those of the Campanian and Maas-
trichtian of western North America. As the only likely
ancestors of the hadrosaur and ceratopsian are from the
Early Cretaceous of Asia, the dramatic shift to faunas
typical of the North American Late Cretaceous is inter-
preted to be the result of opening migration corridors to
and from Asia through Alaska at the end of the Early
Cretaceous, when migration to eastern North America
was still possible. The overlying middle to upper Ceno-
manian Dakota Formation preserves a dinosaur fauna
much like that of the Mussentuchit fauna with the
notable absence of sauropods. The fossil record in the
Cedar Mountain Formation of east-central Utah can be
divided as follows: (1) a basal Barremian iguanodontid-
polacanthid fauna with European affinities predating
common flowering plants; (2) a middle Aptian-middle
Albian Tenontosaurus-Pleurocoelus fauna, perhaps rep-
resenting an impoverished recovery fauna following a
major Lower Cretaceous extinction event (endemic to
North America); (3) an Albian-Cenomanian boundary
fauna dominated by lambeosaurine hadrosaurids with
Asian affinities, when flowering plants were co-domi-
nant, which continued until the end of the Cretaceous.
DISTRIBUTION OF VERTEBRATE FAUNAS IN THE CEDAR
MOUNTAIN FORMATION, EAST-CENTRAL UTAH
James I. Kirkland
Utah Geological Survey, Box 146100, Salt Lake City, UT 84114-6100
Richard L. Cifelli
Oklahoma Museum of Natural History, University of Oklahoma, Norman, OK 73019
Brooks B. Britt
Eccles Dinosaur Park, 1544 East Park Boulevard, Ogden, UT 84401
Donald L. Burge
College of Eastern Utah, Prehistoric Museum, 451 E. 400 N., Price, UT 84501
Frank L. DeCourten
Geology/ Earth Science, Sierra College, 5000 Rocklin Road, Rocklin, CA 95677
Jeffery G. Eaton
Department of Geology, Weber State University, Ogden, UT 84408-2507
J. Michael Parrish
Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115-2854

INTRODUCTION
Historically, the Lower to “middle” Cretaceous ter-
restrial strata of the Cedar Mountain Formation have
been considered to be largely unfossiliferous (Stokes,
1944, 1952; Young, 1960). The uppermost Cedar Moun-
tain Formation in the western San Rafael Swell had been
established as late Albian, based on palynomorphs, by
Tschudy and others (1984). Ages based on freshwater
bivalves, ostracodes, charophytes, and plants, while not
as accurate, are compatible (Mitchell, 1956; Stokes,
1952; Young, 1960). The Cedar Mountain Formation has
subsequently been considered as a homogenous Aptian-
Albian unit in most regional studies (for example, Law-
ton, 1985, 1986; Heller and others, 1986; Heller and
Paola, 1989; Baars and others, 1988).
Additionally, the North American terrestrial verte-
brate record has been considered to be very poor overall
for the “middle” Cretaceous, the notable exception being
the Aptian-Albian Cloverly fauna of southern Montana
(Ostrom, 1970). Largely correlative faunas are known
from the Antlers Formation of Oklahoma, Arkansas, and
northern Texas (Stovall and Langston, 1950; Langston,
1974, Cifelli and others, 1997a), the Paluxy and Twin
Mountains Formations of central Texas (Langston, 1974;
Winkler and others, 1989; 1990), and the Arundel For-
mation of Maryland (Gilmore, 1921; Kranz, 1989, 1996).
Recent research has indicated that there are three dis-
tinct faunas in the Cedar Mountain Formation of east-
central Utah (Kirkland, 1996b; Kirkland and others,
1997). In addition to the fauna similar to the well known
Cloverly fauna, there are both a distinct earlier and a
later fauna. Improved biostratigraphic resolution within
this time interval indicates a more complex regional his-
tory during the Early to “middle” Cretaceous than previ-
ously recognized.
THE CEDAR MOUNTAIN FORMATION AND
ITS VERTEBRATE FAUNAS
The term Cedar Mountain Shale was designated by
Stokes (1944) for the drab variegated slope-forming sedi-
mentary rocks lying between the Buckhorn Conglomer-
ate and the Dakota Formation, with a type section on the
southwest flank of Cedar Mountain, Emery County,
Utah. He characterized the Cedar Mountain Shale as
having slopes covered with abundant carbonate nodules
that are often septarized with agate, barite, and other fill-
ings. Additionally, Stokes (1944) noted an abundance of
elongate sandstone lenses (ribbon sandstones) that repre-
sent abandoned river channels. He also noted the pres-
ence of polished chert pebbles (“gastroliths”).
Stokes (1952) renamed the formation the Cedar
Mountain Formation and included the Buckhorn Con-
glomerate as its basal member (figure 1). His measured
type section (section 9, T. 18 S., R.10 E. of the Salt Lake
Base Line and Meridian) is 123.6 meters thick. He rec-
ognized that the Burro Canyon Formation of western
Colorado (Stokes and Phoenix, 1948) was largely equiv-
alent to the Cedar Mountain Formation and recommend-
ed using the Colorado River as the dividing line between
these formations (Stokes, 1952).
Young (1960), recognizing the continuity of the two
formations, proposed that the term Burro Canyon be
abandoned in favor of Cedar Mountain Formation. This
proposal has been ignored by subsequent authors (Craig,
1981). Young (1960) recognized several regionally
extensive sandstones in the Cedar Mountain Formation
that were useful for correlation (figure 1).
Based on correlations of regionally persistent sand-
stone units, Young (1960) proposed that calcareous mud-
stones assigned to the Cedar Mountain passed eastward
into the carbonaceous sandstones and shales of his Natu-
rita Formation. The more refined biostratigraphy devel-
oped by Kirkland and others (1997) permit more refined
correlations across Utah that preclude correlating any
sandstone bed within the Cedar Mountain Formation
with any specific sandstone bed within the Dakota For-
mation to the east across central Utah. However, subsur-
face data presented by Molenaar and Cobban (1991)
indicate that the upper Cedar Mountain Formation corre-
lates with the upper Dakota Formation northwestward
across the Uinta Basin. Young’s (1960) sandstone corre-
lations suffered from this lack of biostratigraphic control,
but these regionally persistent sandstone units mark
major breaks in sedimentation as indicated by the dra-
matic faunal changes documented herein. Thus Young’s
(1960) recognition of these sandstones represents a sig-
nificant, if belatedly utilized, breakthrough in our under-
standing of the Cedar Mountain Formation.
In addition to the basal Buckhorn Conglomerate of
the western San Rafael Swell, four additional members
of the Cedar Mountain Formation have been defined
(Kirkland and others, 1997). In ascending order, based
on lithostratigraphic and biostratigraphic relationships,
these are Yellow Cat Member, Poison Strip Sandstone,
Ruby Ranch Member, and Mussentuchit Member (figure 1).
Buckhorn Conglomerate
The Buckhorn Conglomerate was defined as a for-
mation by Stokes (1944) for exposures below the dam at
Buckhorn Reservoir on the southwest flank of Cedar
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Figure 1. History of nomenclature for Upper Jurassic through “middle” Cretaceous in east-central Utah. Time scale from Obradovich (1993). After Kirkland and others (1997).

Mountain where its exposed thickness is 7.5 meters. At
the type locality the pebbles have an average diameter of
3 centimeters and are composed mostly of black chert.
The member is largely trough-crossbedded with flow
directions to the northeast. The Buckhorn Conglomerate
is best developed in the northern San Rafael Swell area.
Because of its discontinuous nature, Stokes (1952) sub-
sequently included the Buckhorn Conglomerate as the
lower member of the Cedar Mountain Formation. Young
(1960) also noted that the member is discontinuous and
found that it could not be correlated to any specific sand-
stone east of the San Rafael Swell (figure 1).
Aubrey (1996, 1998) proposed that the Buckhorn
Conglomerate is separated from the overlying strata of
the Cedar Mountain Formation by a calcrete horizon and
that it intertongues with the Morrison Formation and
should be considered Upper Jurassic. Currie (1997) also
recognized this calcrete horizon in the area of northeast-
ern Utah and northwestern Colorado near Dinosaur
National Monument and proposed that it was a sequence-
bounding unconformity within the Lower Cretaceous.
No fossils have been recovered from the Buckhorn Con-
glomerate beyond reworked late Paleozoic invertebrates
and its correlation to the basal members of the Cedar
Mountain Formation to the east is still problematic.
Yellow Cat Member
The Yellow Cat Member is exposed in the northern
Paradox Basin in a belt extending from the west side of
the ancestral Uncompahgre Uplift west of Dewey
Bridge, Utah, to the east side of the San Rafael Swell
(figure 2). At most exposures, the Yellow Cat Member
extends from the basal calcrete of the Cedar Mountain
Formation in this region (Aubrey, 1996, 1998; Kirkland
and others, 1997) up to the base of a regionally extensive
sandstone ledge (middle sandstone of Young, 1960;
Poison Strip Sandstone of Kirkland and others, 1997).
These sediments consist mostly of interbedded mud-
stone, with interbeds of sandstone and limestone. These
mudstones tend to be mauve toward the base and pale
green toward the top. They differ from those of the
Morrison in being drabber and less strongly variegated.
In addition, the mudstones in the Yellow Cat Member are
not smectitic.
The basal calcrete is not always present and at some
sites there is a shale-on-shale contact, although common
polished chert pebbles (“gastroliths”) are generally found
at the best pick for the contact (Stokes, 1944; 1952) sug-
gesting a deflation surface. At other sites, the basal cal-
crete is a complex of superimposed calcretes or there
may be several calcretes and the contact is picked at the
top of the lowest calcrete above smectitic mudstones of
the Brushy Basin Member of the Morrison Formation.
Aubrey (1996, 1998) utilized the base of the calcrete as
the base of the Cedar Mountain, however the basal sur-
face is often gradational. His argument assumes that this
calcrete represents a complex soil horizon developed on
the Morrison paleosurface. However, while distinct soil
features are recognized in many places, in other areas
such as below the type section of the Ruby Ranch Mem-
ber, overlying lucustrine sediments may be a control on
the development these carbonates. The uppermost Mor-
rison below the calcrete is often non-smectitic, root-mot-
tled, and a brick red color, perhaps reflecting the period
of exposure, oxidation, and soil formation between depo-
sition of the Morrison Formation and the onset of Cedar
Mountain deposition.
The type section of the Yellow Cat Member of the
Cedar Mountain Formation is near the Gaston Quarry
(figure 3) west of the Yellow Cat Road (Kirkland and
others, 1997). At this site, the Cedar Mountain Forma-
tion is 45.9 meters thick and the basal Yellow Cat Mem-
ber measures 24 meters thick. At 6.7 meters below the
overlying Poison Strip Sandstone, there is an interval of
limestone and shale interbeds which Young (1960, figure
6, section 37) used to mark the base of the Cedar Moun-
tain Formation in this area. Therefore, a major portion
of the Yellow Cat Member had been included in the
Brushy Basin Member of the Morrison Formation.
The Yellow Cat fauna includes abundant specimens
of a new genus of polacanthid ankylosaur related to
Polacanthus, Iguanodon ottingeri (Galton and Jensen,
1979), perhaps a distinct genus of sail-backed iguan-
odontid, titanosaurid and camarasaurid sauropods, a new
genus of theropod most similar to Ornitholestes, and the
giant dromaeosaurid Utahraptor ostrommaysorum (Kirk-
land and others, 1991; Kirkland, Burge, Britt, and Blows,
1993; Kirkland and others, 1997; Kirkland and others,
1995; Kirkland, 1993, 1996a; Kirkland, Burge, and
Gaston, 1993; Britt and others, 1996; Britt and Stadt-
man, 1997; Carpenter and others, 1996). In addition,
turtles, crocodilians, and a sphenodontian have been rec-
ognized (Kirkland and others, 1997). Fish appear to be
locally abundant, but have been identified only from iso-
lated remains (table 1). Hybodont sharks have been
identified on the basis of a small fragment of dorsal fin
spine and several spiral coprolites rich in ganoid scales.
Important vertebrate quarries in this member include
Brigham Young University’s Dalton Well Quarry (figure
4), which preserves a diverse fauna dominated by
sauropods (Britt and others, 1996; Britt and Stadtman,
1997), and College of Eastern Utah Prehistoric Muse-
um’s Gaston Quarry (figure 3), which preserves a less
204 Utah Geological SurveyVertebrate Paleontology in Utah
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Miscellaneous Publication 99-1 205Vertebrate Paleontology in Utah
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Figure 2. Cross section showing the distribution of “middle” Cretaceous units across eastern Utah discussed in text. Modified after Kirkland and
others (1997). Base map showing distribution of Cedar Mountain, Burro Canyon, and Dakota Formations modified after Young (1960).

diverse fauna dominated by polacanthid ankylosaurs.
Both of these sites are in the upper third of the Yellow
Cat Member. At the base of the Yellow Cat Member 1.5
kilometers east of the Gaston Quarry, one horizon has
yielded several isolated small theropod skeletons (figure
5) (Kirkland and others, 1997). Sites preserving isolated
remains of iguanodontids, sauropods, and polacanthid
ankylosaurs have also been found in the region by the
Denver Museum of Natural History. Important collec-
tions of fossils from this interval are housed at the Col-
lege of Eastern Utah Prehistoric Museum, Price, Utah;
Earth Science Museum, Brigham Young University,
Provo, Utah; Denver Museum of Natural History, Denver
Colorado; and the Oklahoma Museum of Natural Histo-
ry, University of Oklahoma, Norman Oklahoma.
There is disagreement among the authors as to
whether there are one or two iguanodontids in the Yellow
Cat Member. Britt and Stadtman (1997) have proposed
that the sail-backed iguanodontian is an adult specimen
of Iguanodon ottingeri as both specimens occur together
at the type locality. Kirkland and others (1997) have
proposed that there are two iguanodontid taxa, a large
sail-backed form and I. ottingeri; and a conservative
small iguanodontian similar to or even conspecific with
I. lakotaensis (Weishampel and Bjork, 1989). All the
iguanodontid specimens collected at the Gaston Quarry
and found as isolated specimens are similar to the type
specimens of I. ottingeri and I. lakotaensis. Only further
excavations will resolve this question.
The polacanthid ankylosaurs, iguanodontids, and
titanosaurid sauropods indicate close temporal and geo-
graphic ties to the Barremian of Europe (Blows, 1993;
Norman, 1988). This correlation is also supported by the
presence of the charophyte Nodosoclavator bradleyi,
which is not known in strata younger than Barremian
(Niel Shudack, personal communication; Kirkland and
206 Utah Geological SurveyVertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish
Figure 3. Type area of Yellow Cat Member of the Cedar Mountain Formation above Yellow Cat Flat near College of Eastern Utah Prehistoric
Museum’s Gaston Quarry. Arrow indicates position of Gaston Quarry. Abbreviations: cal, calcrete; Cp, Poison Strip Sandstone; Cr, Ruby Ranch
Member; Cy, Yellow Cat Member; D, Dakota Formation; Mor; Morrison Formation.
Table 1. Yellow Cat Fauna (see text for repositories)
Class Osteichthyes
Subclass Dipnoi
Ceratodus undescribed new species
Subclass Actinopterygia
cf. Semionotus ? sp.
cf. Amia sp.
Class Reptilia
Order Chelonia
cf. Glyptops sp.
Order Rhynchocephalia
cf. Toxolophosaurus sp.
Order Crocodilia
indeterminate teeth
Order Theropoda
Family Dromaeosauridae
Utahraptor ostrommaysorum
Family uncertain
Nedcolbertia justinhofmanni
Order Sauropoda
Family Camarasauridae
undescribed new genus
Family Titanosauridae
undescribed new genus
Order Ornithopoda
Family Iguanodontidae
Iguanodon ottingeri
undescribed new genus
Order Ankylosauria
Family Polacanthidae
Gastonia burgei

others, 1997). Furthermore, the dinosaurs indicate a
close correlation with the Lakota Formation at Buffalo
Gap, South Dakota (Kirkland, 1992; Kirkland, Burge,
and Gaston, 1993; Kirkland and others, 1997; Lucas,
1993) (figure 6). Kirkland and others (1997) estimated
that 20 to 25 million years of Earth history may be repre-
sented by the hiatus between Morrison and Cedar Moun-
tain deposition based on radiometric age estimates at the
top of the Morrison Formation (Kowallis and others;
1998) and the age of correlative dinosaur-bearing strata
(Obradovich, 1993; Dyman and others, 1994).
The thickness of the Yellow Cat Member may vary
by tens of meters over several kilometers of outcrop.
Together with the observed differences in its basal con-
tact, this lateral variation in thickness may in part reflect
the topography of the erosional surface formed on the
upper Jurassic strata during the earliest Cretaceous.
The distribution of the Yellow Cat Member provides
an important constraint on the beginning of Sevier thrust-
ing. Aubrey (1996, 1998) has postulated that thrusting
may have begun in the Barremian based on the recogni-
tion of this basal Cedar Mountain fauna (Kirkland,
1992). As a rule, subsidence caused by loading in the
proximal foreland basin is almost instantaneous geologi-
cally, (Turcotte and Schubert, 1982), indicating that age
estimates from the sediment wedge formed proximal to
the thrust belt provide a bracket for the beginning of
thrusting. However, because the Barremian sediments of
the Yellow Cat Member pinch out to the west (figure 2),
they would seem to preclude the onset of Sevier thrust-
ing until at least the Aptian and hence provide additional
support to previously published dates for the onset of
thrusting (Lawton, 1985, 1986; Heller and others, 1986;
Heller and Paola, 1989).
The distribution of the Yellow Cat Member from the
Uncompahgre Uplift to the San Rafael Swell is compati-
ble with the proposal by Aubrey (1996) that the distribu-
tion of these sediments was controlled by salt tectonics
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Figure 4. The Brigham Young University’s Dalton Wells Quarry indicated by D and
brackets. Abbreviations: Cp, Poison Strip Sandstone; Mor, Morrison Formation.
Figure 5. College of Eastern Utah Prehistoric Museum’s small theropod sites indicat-
ed by dots just to the east of the Gaston Quarry. Abbreviations: Cp, Poison Strip Sand-
stone; cal, calcrete.

208 Utah Geological SurveyVertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish
Figure 6. Correlation chart showing age relationships of stratigraphic units discussed in text. Vertical lines denote unconformities. Time scale from
Obradovich (1993). Data from Benton and Spencer (1995), Dyman and others (1994), Hancock and others (1993), and Winkler and others (1995). Modi-
fied after Kirkland and others (1997).

during the Early Cretaceous as reported by Doelling
(1988). Variation in local subsidence rates due to salt
tectonics might help explain the rapid thinning and thick-
ening observed in the Yellow Cat Member. Additionally,
lacustrine sediments such as algal- and mudcracked lime-
stones are common in the Yellow Cat Member (Britt and
Stadtman, 1997; Kirkland and others, 1997). Lacustrine
sediments are compatible with the formation of small
basins due to salt tectonics.
The presence of numerous calcareous nodules repre-
senting paleosols indicates that the Yellow Cat Member
was deposited under a semiarid monsoonal climate simi-
lar to that interpreted for the underlying Morrison For-
mation (Dodson and others, 1980, Wing and Sues, 1992).
The widespread occurrence of viviparid snails, fish,
freshwater turtles, and crocodilians suggest there may
have been more standing water than indicated for the
Late Jurassic of the Colorado Plateau (Dodson and oth-
ers, 1980). The floras recorded for the Barremian are
generally devoid of angiosperms other than a low diver-
sity of pollen types, which first appear in the middle Bar-
remian (Hughes and others, 1979). This would indicate
that a flora dominated by non-flowering plants much like
that of the of the Jurassic was present (Wing and Sues,
1992).
Poison Strip Sandstone
The cliff-forming middle Cedar Mountain sandstone
unit of Young (1960) marks the top of the Yellow Cat
Member in eastern Utah (figure 1). It commonly con-
tains gray and white chert pebbles In some places there
are several sandstones that are probably genetically relat-
ed to each other, while rarely in other places there is only
a thin crevasse splay or, locally, no sandstone at all. This
sandstone above the Yellow Cat Member has been
named the Poison Strip Sandstone (Kirkland and others,
1997). It caps the escarpment exposing the upper Morri-
son Formation throughout the area from Green River,
Utah to the Utah-Colorado border. This sandstone forms
one of the most persistent and distinctive stratigraphic
intervals in the entire Cedar Mountain Formation of east-
ern Utah. In some areas in the Poison Strip region south
of Cisco, Utah, large scale (5 meters and greater) epsilon
cross-bedding indicates that a large, meandering river
system was mostly responsible for its deposition.
The Poison Strip Sandstone is clearly equivalent to
Young’s (1960) middle Cedar Mountain sandstone east
of the San Rafael Swell. However, the middle Sandstone
unit as used by Young (1960) in the western San Rafael
Swell area is well above sites preserving an Aptian-lower
Albian fauna, such as at the Long Walk Quarry (DeCour-
ten, 1991; Kirkland and others, 1997), and appears to be
an unrelated sandstone of more limited extent. Without
the biostratigraphic control provided by the vertebrate
faunas preserved in the Cedar Mountain Formation,
Young’s (1960) miscorrelation of these sandstones across
the San Rafael Swell is understandable.
Sedimentologically the Poison Strip Sandstone is
clearly distinct from the trough cross-bedded conglomer-
ate of the Buckhorn Member of the Cedar Mountain For-
mation in the San Rafael Swell area. Although apparent-
ly in the same stratigraphic positions, there is no means
of correlation between the genetically distinct Buckhorn
Conglomerate and the middle sandstone of Young (1960)
in eastern Utah. In the western San Rafael Swell area,
no fossils have been found in the Buckhorn Conglomer-
ate at the base of the Cedar Mountain Formation; thus it
impossible as yet to date the Buckhorn. Additionally,
Currie (1997) describes the Buckhorn Conglomerate as
Miscellaneous Publication 99-1 209Vertebrate Paleontology in Utah
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Figure 7. The Brigham Young University’s Bodily’s Nodosaur Site on west side of Arches National Park. Arrow points to site. Abbreviations: Cm,
Mussentuchit Member; Cp, Poison Strip Sandstone; Cr, Ruby Ranch Member; Cy, Yellow Cat Member; D, Dakota Formation; Mor, Morrison For-
mation.

representing an isolated river system flowing to the
northeast from the San Rafael Swell across the extreme
northwestern corner of Colorado into Wyoming.
The Poison Strip Sandstone is named for the typical
exposures of this unit along the Poison Strip south-south-
west of Cisco, Utah. The type section is on the south-
west end of the Poison Strip east-northeast of the Ring-
tail Mine (Kirkland and other, 1997) (figure 4). The type
section of the Poison Strip Sandstone measures 5.4
meters thick. The sandstone is fine- to medium-grained
with matrix supported black, gray, and white chert peb-
bles, trough cross-bedded, and becomes slabby with pale
greenish mudstone partings toward the top of the mem-
ber. The Poison Strip Sandstone is economically signifi-
cant in this area because it is the primary target in the
Cisco Oil and Gas Field to the northeast (Larry Moyer,
personal communication, 1995).
On the northeast side of Arches National Park, Bodi-
ly (1969) described a large ankylosaur as cf. Hoplitos-
aurus sp. from in, or just above this unit (figure 5).
Coombs (1971) referred the taxon to the Cloverly
nodosaurid ankylosaur, Sauropelta. Just north of this site
a second specimen of Sauropelta was recently discov-
ered by researchers from the Denver Museum of Natural
History. These fossils indicate the Poison Strip Sand-
stone is close to the same age as the overlying Ruby
Ranch Member, which also contains Sauropelta. The
College of Eastern Utah Prehistoric Museum has recov-
ered parts of an ornithopod from their Price River Quarry
from a conglomeratic sandstone at the base of the Cedar
Mountain Formation, southeast of Wellington, Utah
(Burge, 1996). The ornithopod appears to represent
Tenontosaurus and suggests that the conglomeratic sand-
stone southeast of Wellington correlates to the Poison
Strip Sandstone. The sparse, small, black, gray, and
white chert pebbles are also similar to those in the Poi-
son Strip Sandstone. Large conifer logs and the cycads,
Cycadeoidea and Monanthasia (William Tidwell, person-
al communication, 1997) are present locally within the
Poison Strip Sandstone in the area around Arches
National Park.
Ruby Ranch Member
The Ruby Ranch Member extends across the entire
outcrop belt of the Cedar Mountain Formation and in
strata assigned to the Burro Canyon Formation east of
the Colorado River (figure 2). The Ruby Ranch Member
overlies the Poison Strip Sandstone from at least the
Utah-Colorado border region westward to the eastern
San Rafael Swell and overlies the Buckhorn Conglomer-
ate on the west side of the San Rafael Swell. From
approximately the crest of the Salt Valley Anticline at
Arches National Park eastward, the upper contact of the
Ruby Ranch Member is clearly with the base of the
Dakota Formation. On the west side of the San Rafael
Swell, a sharp break from carbonate nodule-bearing,
non-smectitic strata to carbonaceous, highly smectitic
strata marks the contact between the Ruby Ranch Mem-
ber and the overlying Mussentuchit Member. A con-
glomerate unit rich in quartzite lies between these mem-
bers along the northeastern side of the San Rafael Swell
that is equivalent for the most part to Young’s (1960)
middle Naturita sandstone ( Mark Kirschbaum, personal
communication, 1996; Kirkland and others, 1997).
On the west side of Arches National Park a smectitic
interval is present at the top of the Cedar Mountain For-
mation. This interval potentially correlates with the
Mussentuchit Member of the western San Rafael Swell
(figure 2). The report of a hadrosaur femur (Galton and
Jensen, 1979) from this area may lend support to that
correlation. Additionally, Brigham Young University’s
“Movie Valley” ankylosaur from the same area, may also
be from this level based on the black color of the bones,
which uniquely characterizes bones preserved in the
Mussentuchit Member among units in the Cedar Moun-
tain Formation.
The Ruby Ranch Member consists of drab, variegat-
ed mudstones with minor sandstone and limestone lay-
ers. Perhaps most characteristic of this interval are the
abundant carbonate nodules that often are so abundant as
to form a pavement covering the exposed slopes. The
abundance of these nodules makes prospecting for fossils
in this interval difficult. In addition, ribbon sandstone
bodies holding up ridges that may extend for a kilometer
or more are typical of this interval (Young, 1960; Harris,
1980; DeCourten, 1991; Kirkland and others, 1997). A
substantial portion of the northwestward thickening
observed in the Cedar Mountain Formation across the
San Rafael Swell (for example, Stokes, 1952; Young,
1960) is represented by this interval. There is also a con-
siderable thinning and thickening of this interval along
the west side of the San Rafael Swell.
The type section of the Ruby Ranch Member is at
the Ruby Ranch homestead site southwest of Crescent
Junction, Utah (Kirkland and others, 1997). The basal
contact is with the Poison Strip Sandstone and the upper
contact is with the base of the Dakota Formation. The
type section is 33.1 meters thick. At 2.1, 14, and 16.6
meters above the base, ribbon sandstones, whose thalweg
and cross-bed orientations represent eastward-flowing
rivers are present. Overall, the drab, variegated mud-
stones have a pale purplish surface expression. The
upper 8.5 meters is a pale, greenish-gray color perhaps
due to bleaching by the overlying Dakota Formation.
210 Utah Geological SurveyVertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish

This upper interval also includes fewer, but larger car-
bonate nodules.
The Ruby Ranch fauna (table 2) includes the primi-
tive iguanodontid Tenontosaurus?, the large nodosaur
Sauropelta, a sauropod assigned to Pleurocoelus (= Ast-
rodon), dromaeosaurid teeth, an unidentified large thero-
pod, and Acrocanthosaurus (Weishampel and Weisham-
pel, 1983; DeCourten, 1991; Kirkland and others, 1997).
This fauna is the least known of the Cedar Mountain fau-
nas. Important vertebrate sites in this member include
the University of Utah’s Long Walk Quarry near Cas-
tledale (DeCourten, 1991), the College of Eastern Utah’s
Price River 2 and KEM sites southeast of Wellington,
Utah, and the Oklahoma Museum of Natural History’s
Hotel Mesa Quarry (figure 8) just to the east of the Col-
orado River, and thus what properly should be consid-
ered a Burro Canyon Formation site (Kirkland and oth-
ers, 1997). The site, from which the Tenontosaurus
specimens were collected on the west side of the San
Rafael Swell (Weishampel and Weishampel, 1983), has
not been relocated, but the carbonate matrix surrounding
the specimens indicates they are from the Ruby Ranch
Member. Important collections of fossils from this mem-
ber are housed at the College of Eastern Utah Prehistoric
Museum, Price, Utah; Earth Science Museum, Brigham
Young University, Provo, Utah; and the Utah Museum of
Natural History, University of Utah, Salt Lake City,
Utah.
This fauna compares well with those documented
from the Cloverly Formation, Arundel Formation, and
Trinity Group characteristic of North America’s appar-
ently endemic Aptian-Lower Albian dinosaur fauna
(Kirkland, 1996b; Kirkland and others, 1997). Deter-
mining the age of these sediments more precisely is
impossible at this time.
The abundant calcareous nodules indicate that the
Ruby Ranch Member was deposited under a semiarid
monsoonal climate similar to that interpreted for the
underlying Morrison Formation (Dodson and others,
1980, Wing and Sues, 1992). The Aptian-Albian pollen
record indicates that angiosperms were becoming a sig-
nificant part of western interior floras at this time (Wing
and Sues, 1992).
Mussentuchit Member
A sharp break from carbonate-nodule-bearing, non-
smectitic strata to carbonaceous, highly smectitic strata
marks the base of the Mussentuchit Member. The dra-
matic increase in the volume of volcanic ash preserved in
the Mussentuchit Member indicates a significant increase
in volcanic activity to the west. The member is dated as
straddling the Albian-Cenomanian boundary based on
palynology (Nichols and Sweet, 1993), subsurface corre-
lations (Molenaar and Cobban, 1991), and radiometric
age estimates (Cifelli and others, 1997b).
Miscellaneous Publication 99-1 211Vertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish
Table 2. Ruby Ranch Fauna (see text for repositories)
Class Chondrichthyes
Order Hybodontoidea
Hybodus sp.
Class Reptilia
Order Crocodilia
indeterminate
Order Theropoda
Family Dromaeosauridae
cf. Deinonychus sp.
Family Allosauridae ?
undescribed new genus
cf. Acrocanthosaurus sp.
Order Sauropoda
Family Brachiosauridae
Pleurocoelus sp. = Astrodon sp.
Order Ornithopoda
Family Iguanodontidae
Tenontosaurus sp.
Order Ankylosauria
Family Nodosauridae
cf. Sauropelta sp.
Figure 8. Oklahoma Museum of Natural History’s Hotel Mesa Site indicated by arrow looking east across the Colorado River. Abbreviations: Cp,
Poison Strip Sandstone; D, Dakota Formation; Mor, Morrison Formation.

Stokes (1944) included this member in the Cedar
Mountain Shale. However, he described the Cedar
Mountain as having abundant carbonate nodules and did
not mention that, at the top of the unit, the formation
may lack such nodules.
Locally in the area of the southwestern San Rafael
Swell south of Interstate 70, sandstone lenses near the
top of the Cedar Mountain Formation compare well with
the more extensive sandstone ledge typically used to
define the base of the Dakota Formation (Stokes, 1944).
This transition suggests that the top of the Cedar Moun-
tain Formation may represent a period of nearly continu-
ous sedimentation including the more carbonaceous
overlying Dakota Formation. In fact, Young (1960)
included the Mussentuchit Member in his Naturita For-
mation (Dakota Formation). The dramatic shift in the
sedimentology and paleontology at the base of this inter-
val suggests that perhaps the Mussentuchit Member
would be better included as a basal member of the Dako-
ta Formation; the authors of this paper are not in full
agreement at to whether this member should be included
in the Cedar Mountain Formation or in the Dakota For-
mation (Kirkland and others, 1997). However, including
the Mussentuchit Member in the basal Dakota Formation
would mean that nearly every fossiliferous horizon in the
area of the western San Rafael Swell attributed to the
Cedar Mountain Formation (Katich, 1951; Stokes, 1952;
Thayne and others, 1983, 1985; Thayne and Tidwell,
1984; Tidwell and Thayne, 1985; Jensen, 1970; Eaton
and Nelson, 1991; Cifelli, 1993; Kirkland and Burge,
1994; Cifelli and others, 1997b, this volume), would
have to be attributed to the Dakota Formation.
212 Utah Geological SurveyVertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish
Figure 9. Type area of Mussentuchit Member of the Cedar Mountain Formation, Mussentuchit Wash near several of the Oklahoma Museum of
Natural History’s quarries. Dashed line indicates contact between Ruby Ranch and Mussentuchit Members. Abbreviations: Cb, Buckhorn Conglom-
erate; Cp, Poison Strip Sandstone; Cr, Ruby Ranch Member; Cy, Yellow Cat Member; D, Dakota Formation.
Figure 10. College of Eastern Utah Prehistoric Museum’s Carol Site indicated by arrow northwest of Castledale, Utah. Abbreviations: Cr/Cm,
contact between Ruby Ranch and Mussentuchit Members; D, Dakota Formation.

The upper smectitic portion of the Cedar Mountain
Formation was designated the Mussentuchit Member by
Kirkland and others (1997) with its type section south of
Mussentuchit Wash (figure 9). At the type section, the
member is 25 meters thick. A thin, discontinuous sand-
stone marks the base, where the non-smectitic mudstone
rich in carbonate nodules is replaced by highly smectitic,
gray mudstone. Several thin lenticular sandstones and
lignitic horizons are present in the type section. The top
of the member is at the base of a thick buff sandstone
that forms the basal unit of the Dakota Formation along
most of the western San Rafael Swell. Locally to the
east of Ferron Utah, the Dakota Formation is missing
(figure 2) and a horizon of dark chert pebbles and cob-
bles marks the base of the overlying Mancos Shale
(Eaton and others, 1990; Kirkland and others, 1997).
The preserved dinosaur fauna includes a small
nodosaurid Animantarx ramaljonesi, a small iguanodon-
tid ornithopod, a primitive lambeosaurid hadrosaur, cer-
atopsian teeth, pachycephalosaur teeth, tiny sauropod
teeth, dromaeosaurid teeth, cf. Richardoestesia teeth, cf.
Paronychodon teeth, and an early tyrannosaurid (Kirk-
land and Burge, 1994; Kirkland and Parrish, 1995;
Burge, 1996; Carpenter and others, this volume). Teeth
of a very small sauropod similar in morphology to those
described as Astrodon are also present in this member
marking the last occurrence of sauropods in North Amer-
ica prior to their reintroduction from South America in
the late Maastrichtian (Lucas and Hunt, 1989). At the
family level, this fauna is remarkably similar to those of
the overlying Dakota Formation (Eaton and others, 1997)
and those of the Campanian and Maastrichtian of west-
ern North America (Cifelli, Kirkland, and others, 1997b;
Cifelli and others, this volume; Kirkland, 1996b; Kirk-
land and others, 1997). As the only likely ancestors of
the hadrosaur, ceratopsian, and perhaps the tyrannosaurid
are from the Early Cretaceous of Asia, the dramatic shift
to faunas typical of the North American Late Cretaceous
is interpreted to be the result of opening migration corri-
dors to and from Asia through Alaska at the end of the
Early Cretaceous, when migration to eastern North
America was still possible (Kirkland, 1996b; Cifelli and
others, 1997b).
Following an extensive screenwashing operation by
the University of Oklahoma that resulted in thousands of
catalogued specimens representing nearly 80 vertebrate
taxa, Cifelli, Kirkland, Kirkland, and others (1997; and
Cifelli and others, this volume, for complete faunal list)
have characterized this fauna as the Mussentuchit local
fauna for Mussentuchit Wash, where many of their best
vertebrate sites are located.
In addition to the many important sites developed by
the Oklahoma Museum of Natural History, a number of
other important vertebrate sites have been developed in
the Mussentuchit Member by other institutions. Most of
these sites are from the area east of Ferron and Castle
Dale, Utah and include the Carol Site (figure 10), the
Rough Road Quarry, Jensen’s egg site, and Robison’s
Eggshell Quarry ( Jensen, 1970; Nelson and Crooks,
1987; Pomes, 1988; Eaton and Nelson, 1991; Jones and
Burge, 1995; Burge, 1996). Important collections from
these sites are housed at the College of Eastern Utah Pre-
historic Museum, Price, Utah; Sternberg Museum, Hays,
Kansas; University of Colorado Museum, Boulder, Col-
orado; University of California, Museum of Paleontol-
ogy, Berkeley, California; Brigham Young University,
Earth Science Museum, Provo, Utah; and the Oklahoma
Museum of Natural History, Norman, Oklahoma.
The most common dinosaur from the Mussentuchit
Member is a primitive hadrosaurid (Kirkland and Burge,
1994; Kirkland and others, 1997). Common hadrosaurid
teeth from Cedar Mountain Formation sites on the west
side of the San Rafael Swell were first noted by Parrish
(1991), although the locality horizon was not indicated in
that abstract. The senior author has determined this
primitive hadrosaurid to be somewhat like Telmatosaurus
(Weishampel and others, 1993) from the Upper Creta-
ceous of eastern Europe and a bit more advanced than
the iguanodontid Probactrosaurus (Rozhdestvensky,
1967; Norman, 1990) from the Lower Cretaceous of cen-
tral Asia. More research is needed to determine its sys-
tematic position relative to the Hadrosaurinae and Lam-
beosaurinae (Sereno, 1986; Horner, 1990; Weishampel
and Horner, 1990). However, the material discovered to
date suggests lambeosaurine affinities.
Molenaar and Cobban (1991) have demonstrated
through subsurface relationships that the uppermost
Cedar Mountain Formation may correlate to the Mowry
Shale to the northeast and may thus be of basal Ceno-
manian age. The Albian-Cenomanian boundary, on the
basis of non-marine palynomorphs, has been placed at
the first occurrence of tricolporate pollen grains (for
example Nyssapollenites, rare in marine rocks) and obli-
gate tetrads (Singh, 1975; Nichols and Sweet, 1993).
Tschudy and others (1984) did not encounter these paly-
nomorphs in their samples from the upper Cedar Moun-
tain Formation near Castle Dale, Utah. The occurrence
of these palynomorphs is diachronous across Alberta
(Nichols and Sweet, 1993). In addition, with the older
placement of the Albian-Cenomanian boundary (Cobban
and Kennedy, 1989) by ammonite correlations to the
type areas in Europe, it is likely that the palynomorph
datum (first occurrence of tricolpate and obligate tetrad
pollen) is above the base of the Cenomanian (Nichols
Miscellaneous Publication 99-1 213Vertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish

and Sweet, 1993).
A radiometric age estimate of 98.39 ± 0.07 million
years B. P. (Cifelli, Kirkland, and others, 1997) places
the fauna at, or just above, the Albian-Cenomanian
boundary according to the most recent time scales for the
Cretaceous, which have the boundary placed at 98.5 mil-
lion years B. P. (Obradovich, 1993) or at 98.9 ± 0.6 mil-
lion years B. P. (Gradstein and others, 1994). The date
supports a correlation with the Mowry Shale to the
northeast (figure 6).
The absence of calcareous nodules indicates that the
Mussentuchit Member was deposited under a significant-
ly wetter environment than were the lower members of
the Cedar Mountain Formation. This wetter environment
may be due to the transgression of the Mowry Sea into
the area of the northeastern Uinta Basin (Wing and Sues,
1992). The North American plant record indicates that
angiosperms were becoming a more important part of
western interior floras at this time (Wing and Sues, 1992)
and some of the earliest records of some angiosperm
wood types are from this member (Tidwell, 1996).
A dramatic shift between Albian and middle Ceno-
manian faunas has been noted in Texas (Lee, 1995; Win-
kler and others, 1995). The new age estimates for the
Mussentuchit Member indicate that this faunal turnover
was even more dramatic than was previously thought.
Thus, within the Cedar Mountain Formation there is a
three-fold instead of a two-fold zonation of Cedar Moun-
tain Formation based on dinosaurs (Kirkland, 1992,
1996b; Lucas, 1993): a basal Barremian iguanodont-
polacanthid fauna with European affinities predating
common flowering plants; a middle Aptian-middle
Albian Tenontosaurus-Pleurocoelus fauna perhaps repre-
senting a depauperate fauna following a major Early Cre-
taceous extinction event (endemic to North America);
and an upper latest Albian-lowest Cenomanian hadrosaur
fauna with Asian affinities when flowering plants were
co-dominant with gymnosperms. Biogeographic rather
than floristic changes may account for most of the fau-
nistic changes recorded at the end of the Albian as sug-
gested by the dramatic shift to a dinosaur fauna dominat-
ed by taxa with an Asian ancestry (Kirkland, 1996b;
Cifelli and others, 1997b, this volume).
CONCLUSIONS
Vertebrate fossils are present throughout the Cedar
Mountain Formation of east-central Utah. It contains
three distinct faunas, which are separated by intraforma-
tional unconformities. The recognition of these faunas
combined with lithologic observations has permitted
division of the Cedar Mountain Formation into five
members: the Buckhorn Conglomerate, the Yellow Cat
Member, the Poison Strip Sandstone, the Ruby Ranch
Member, and the Mussentuchit Member (Kirkland and
others, 1997). Of these, only the Buckhorn Conglomer-
ate has not yielded age-diagnostic fossils permitting its
correlation with other strata.
The oldest fauna is preserved in the Yellow Cat
Member and is dated as Barremian based on the occur-
rence of dinosaurs similar to those preserved in Barrem-
ian sediments of northwestern Europe, and based on the
occurrence of charophytes not recorded in strata younger
than Barremian. The middle fauna is preserved in the
Poison Strip Sandstone and Ruby Ranch Member and is
dated as broadly Aptian-Albian based on dinosaurs
known to occur elsewhere in North America during the
Aptian-Albian. The youngest fauna is preserved in the
Mussentuchit Member and is precisely dated as overlap-
ping the Albian/Cenomanian boundary at 98.39 ± 0.07
million years B. P. (Cifelli, Kirkland, and others, 1997).
The vertebrate faunas preserved in the Cedar Moun-
tain Formation of east-central Utah provide a unique
opportunity to study the transition of the terrestrial biota
from an environment when angiosperms were rare until
angiosperms were a major component of the flora. Addi-
tionally, these faunas record a shift from a Barremian
fauna with European affinities to an Albian/Cenomanian
fauna with Asian affinities. The transition from sedi-
ments largely devoid of carbonaceous material and con-
taining abundant carbonate nodules, to sediments that are
lignitic with no carbonate nodules, suggests increased
rainfall in the region during the expansion of the Creta-
ceous Western Interior Seaway. Further research in the
region is required to differentiate the relative effects of
changes in the flora, climate, and biogeography on the
terrestrial biota preserved in the Cedar Mountain Form-
ation.
ACKNOWLEDGMENTS
We would like to thank the many people too numer-
ous to count who have helped in the field, including
many from the Utah Friends of Paleontology, Uncom-
pahgre Plateau Paleontological Society, and the Western
Interior Paleontological Society. Special thanks are
extended to the Judd family of Castle Dale, Utah, the
Jones family of Salt Lake City, Utah, the Gaston family
of Knoxville, Tennessee, and the Corbett family of
Raleigh, North Carolina. Robert Young of Grand Junc-
tion, Colorado is gratefully acknowledged for providing
copies of his extensive field notes on the Cedar Moun-
tain and Dakota Formations. Excavations were all
undertaken under permits issued by the Bureau of Land
214 Utah Geological SurveyVertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish

Management and the Utah School and Institutional Trust
Lands Administration. Partial funding in support of this
research was provided by the National Geographic Soci-
ety (grants 4761-91 and 5021-92 to RLC; 5263-94 to
JIK) and the National Science Foundation (grants BSR
8906992 and DEB 941094 to RLC). Special thanks are
due to John Bird and Carl Limone, CEU Prehistoric
Museum; Harold Bollan, Dinamation International Soci-
ety; Randy Nydam, Oklahoma Museum of Natural His-
tory; Rod Scheetz, Museum of Western Colorado; Ken
Stadtman, Brigham Young University; and Scott Madsen,
Dinosaur National Monument for their skilled field assis-
tance and preparation skills. Reviews of this manuscript
by David D. Gillette, Louis L. Jacobs, and Mark Kirsh-
baum are gratefully acknowledged. Innumerable col-
leagues throughout our profession have aided this
research with their knowledge, advice, encouragement,
and camaraderie.
Miscellaneous Publication 99-1 215Vertebrate Paleontology in Utah
Distribution of Vertebrate Faunas - Kirkland, Cifelli, Britt, Burge, DeCourten, Eaton, Parrish
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218 Utah Geological SurveyVertebrate Paleontology in Utah
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