Cedar Mountain Formation Research Articles

Recognition of Paleogastroliths from the Lower Cretaceous Cedar Mountain Formation, Utah using a Scanning Electron Microscope

Paleogastroliths, as defined in this study, are stomach stones associated exclusively with extinct animals. Definitive recognition of paleogastroliths is problematic and controversial. Polished, rounded stones found within skeletal remains of dinosaurs and plesiosaurs are the strongest evidence. This study examined intraskeletal and proposed paleogastroliths using a scanning electron microscope (SEM) to determine if any defining surface textures occur. Paleogastroliths associated with the skeletal remains of Seismosaurus hallorum, possible paleogastroliths from the Lower Cretaceous Cedar Mountain Formation, and other well-polished stones were obtained. Most stones were composed of either quartzite or chert and were examined with a SEM at magnifications ranging from 100× to 400×. All of the cherty Seismosaurus hallorum stones contained sets of parallel to sub-parallel, curved polish grooves that in places crosscut one another. These grooves are inferred to have formed as the result of small particles lodged in the stomach muscles interacting with the stones due to muscle movement. The distinctive surface textures noted on the cherty Seismosaurus hallorum paleogastroliths are similar to those seen on the cherty possible paleogastroliths from the Cedar Mountain Formation. Therefore, the geologic occurrence combined with the microscopic surface texture supports the interpretation that these stones are paleogastroliths.

A Suite of Dermestid Beetle Traces on Dinosaur Bone from the Upper Jurassic Morrison Formation, Wyoming, USA

Most studies of insect traces on fossil bone deal with one or two trace morphs found on isolated bone fragments, making it difficult to identify the trace-maker and its behavior. We report the discovery of a suite of insect traces on an articulated Camptosaurus dinosaur skeleton that permits the identification of the trace-maker and interpretations of its behavior. The traces include mandible marks, pits, and shallow bores on cortical bone, and deep, meandering furrows and tunnels (borings) on articular surfaces. The interiors of bones are intensely mined, and the cavities and borings are filled with fine bone fragments (insect frass). The distinctive mandible marks consist of opposing sets of parallel grooves, indicating the maker had two apical teeth set on symmetrical mandibles and that all of the traces were made by a single taxon. Comparison of the fossils with the mandible morphology and bone traces of extant insects indicates dermestid beetles made the traces. Based on extant dermestid behavior, soft tissues were likely absent and the bones were lipid-laden when the traces were made. Examination of more than 5,000 bones from the Morrison and Cedar Mountain formations shows insect traces on bone are common but overlooked and that many bones are substantially damaged by insect mining. The key to the recognition of these important yet subtle traces is a search model and an intense, oblique light source.

RARE EARTH ELEMENT GEOCHEMISTRY AND TAPHONOMY OF THE EARLY CRETACEOUS CRYSTAL GEYSER DINOSAUR QUARRY, EAST-CENTRAL UTAH

Abstract The Crystal Geyser Dinosaur Quarry contains a large monospecific accumulation of bones from a basal therizinosaur, Falcarius utahensis. The quarry is located approximately 16 km south of Green River, Utah, at the base of the early Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. Fossil bones in the quarry occur in three units that have distinct taphonomic, lithologic, and geochemical characteristics. Rare earth element compositions of fossils suggest that bones from each unit were drawn from different reservoirs or sources having distinctly different compositions, and fossils were not reworked between units. Compositions of bones differ greatly within Units 1 and 2, even within the same 1-m2 quarry grid. These chemical differences and taphonomic characteristics, such as current orientation, hydraulic sorting, and occasional extensive abrasion, suggest that bones from these two units are allochthonous and were fossilized at other localities, possibly over an area of severa...

Tectonic Control on the Sequence Stratigraphy of Nonmarine Retroarc Foreland Basin Fills: Insights from the Upper Jurassic of Central Utah, U.S.A.

Abstract Continental successions of the North American Western Interior retroarc foreland basin provide an excellent opportunity to evaluate the tectonic controls on nonmarine sequence stratigraphy. The transition between the Upper Jurassic Brushy Basin Member anastomosed fluvial system of the Morrison Formation and the gravelly braided-river deposits of the Buckhorn Conglomerate has been studied to assess the dispersal of coarse clastics and the development of associated basin-wide unconformities in a sequence stratigraphic framework. The sharp contact between the two members is interpreted to be conformable based on stratigraphic, sedimentologic, and petrologic data collected at and near Cedar Mountain in central Utah, while a regional, mature paleosol at the top of the Buckhorn Conglomerate indicates the presence of a major sequence boundary. These interpretations are combined with paleoflow data and fluvial architectural analysis to reconstruct the evolution of the alluvial equilibrium profiles that controlled deposition of the succession. The Buckhorn Conglomerate is interpreted as an example of a post-orogenic deposit on the basis of (1) its tabular geometry, (2) distance from the contemporaneous thrust belt, (3) shift to transverse paleoflow direction from the preceding Brushy Basin axial drainage, (4) conformable lower contact, and (5) presence of an overlying sequence boundary with a westward-expanding hiatus eroding the coeval foredeep. The onset of a protracted period of low rate of orthogonal convergence between the Farallon and North American Plates resulted in tectonic quiescence and consequent isostatic rebound of the Middle to Late Jurassic thrust belt and the contiguous contemporaneous foredeep, as well as dynamic uplift. The ensuing basin-wide decrease in subsidence rate induced the progradation of the Buckhorn alluvial plain into the Morrison back-bulge depozone, and the subsequent generation of the overlying pedogenic unconformity, which separates the deposits of the Jurassic flexural event from the overlying Sevier tectonostratigraphic unit.

A multidisciplinary study of the Lower Cretaceous Cedar Mountain Formation, Mussentuchit Wash, Utah: a determination of the paleoenvironment and paleoecology of the Eolambia caroljonesa dinosaur quarry

A quarry within the Cedar Mountain Formation in Mussentuchit Wash, Emery County, Utah, produced a fossil assemblage containing the remains of at least eight juvenile iguanodontid dinosaurs ( Eolambia caroljonesa). The Cedar Mountain Formation lies stratigraphically between the Tithonian–Berriasian (Upper Jurassic) Brushy Basin Member of the Morrison Formation and the Cenomanian (Upper Cretaceous) Dakota Formation. Detailed stratigraphic, sedimentological, geochronological, palynological, and paleontological data have been collected along a measured section at the site of the Cifelli #2 Eolambia caroljonesa Quarry. These data provide a chronostratigraphic and a biostratigraphic framework for the Cedar Mountain Formation and allow a detailed reconstruction of the paleoenvironment and the paleoecology of the local paleogeographic area from which E. caroljonesa have been recovered. Three 40Ar/ 39Ar ages ranging from 96.7 to 98.5 Ma have been obtained three stratigraphically distinct altered volcanic ash layers within the Mussentuchit Member, one of which passes through the E. caroljonesa quarry, that indicate that the quarry is latest Albian in age and that the stratigraphic boundary between the Mussentuchit Member of the Cedar Mountain Formation and the overlying Dakota Formation is at or near the Albian/Cenomanian boundary. Sedimentological and biostratigraphic data suggest that significant long-term and short-term climatic changes are recorded in the Cedar Mountain Formation. During deposition of the lower part of the formation, climatic conditions were warm and arid to semi-arid. During deposition of the upper part of the formation, conditions became more humid. The progressive change in climatic conditions was probably related to the transgression of the Mowry Sea from the north. Cyclic sedimentation in the Mussentuchit Member suggests high-frequency changes from wet to dry periods.

SEDIMENTOLOGY, STRATIGRAPHY, AND DEPOSITIONAL ENVIRONMENT OF THE CRYSTAL GEYSER DINOSAUR QUARRY, EAST-CENTRAL UTAH

Abstract The Crystal Geyser Dinosaur Quarry, near Green River, Utah, is located at the base of the Lower Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. The quarry preserves a nearly monospecific accumulation of a new basal therizinosauroid, Falcarius utahensis. We used field descriptions and petrographic analysis to determine the depositional environment and development of the quarry strata. Results of these analyses suggest that the quarry represents multiple episodes of bone accumulation buried by spring and overbank flood deposits. Evidence for these previously undescribed spring deposits includes calcite macroscopic structures within the quarry strata—such as pisolites and travertine fragments—and calcite micromorphologies—including radial-fibrous, feather, and scandulitic dendrite morphologies and tufa clasts. At least two episodes of bone incorporation are preserved in the quarry based on their stratigraphic position and lithologic associations. The unique depositional set...

Giant dinosaur eggs from the Tiantai basin, Zhejiang Province, China

Giant dinosaur eggs occur within the mid-Cretaceous Liangtoutang Formation of the Tiantai basin in Zhejiang Province of southeastern China. The 43 cm × 14.5 cm eggs represent the first discovery of Macroelongatoolithus xixiaensis specimens from the region. The eggshell exhibits variation in surface ornamentation and eggshell thickness, with smoother and thicker eggshell characteristic of the poles. The Tiantai eggs differ from the stratigraphically younger type specimen of Macroelongatoolithus xixiaensis from Henan Province in their mammillary to continuous layer ratio. Three new features potentially useful for phylogenetic analysis and previously unreported in Macroelongatoolithus and other eggs in the oofamily Elongatoolithidae include prismatic columns, tabular structure within the prisms, and "splaying" of the crystals in the upper mammillae that extend into the overlying continuous layer. Microstructural features of the two nearly complete eggs suggest that the specimens are referable to a potentially large theropod dinosaur. Paleogeographic distribution of these large theropod eggs includes the Late Cretaceous Zoumagang Formation of Henan Province and the mid-Cretaceous Liangtoutang Formation of Zhejiang Province in central and southeastern China and possibly the Lower Cretaceous Cedar Mountain Formation and mid-Cretaceous Dakota Formation of Utah, USA.

The pectoral girdle and forelimb of the primitive therizinosauroid Falcarius Utahensis (Theropoda, Maniraptora): analyzing evolutionary trends within Therizinosauroidea

ABSTRACT The recent discovery of a dense, paucispecific bonebed from the Early Cretaceous Cedar Mountain Formation, central Utah, has yielded new information on the morphology and evolution of therizinosaurs. Detailed description of the pectoral girdle and forelimb of Falcarius utahensis—the predominant taxon recovered from this site—provides the basis for a species-level, phylogenetic investigation of this enigmatic group. The analysis, consisting of 32 characters arrayed among 13 taxa, supports previous assertions that Falcarius represents the basal-most known member of the clade. The analysis further supports a monophyletic Therizinosauroidea on the basis of seven unambiguous synapomorphies of the pectoral girdle and forelimb. Contrary to previous hypotheses, analysis of the pectoral girdle and forelimb suggests that Therizinosauridae is more appropriately defined as a derived clade including Nothronychus, Erlicosaurus, Neimongosaurus, Therizinosaurus, and Segnosaurus. Equally strong support is recovered for a clade containing these five genera plus “Alectrosaurus” and Erliansaurus. The morphology of primitive therizinosauroids—characterized by Falcarius, Beipiaosaurus, and Alxasaurus—suggests that Early Cretaceous taxa already exhibited the beginnings of a trend toward increased robustness and altered range of motion of the pectoral girdle and forelimb. Derived therizinosaurs exhibit an amplification of these evolutionary trends as well as increased dorsal reach, increased wrist flexibility, and severe reduction in manual digit length. The functional reorganization of the pectoral girdle and forelimb throughout the evolutionary history of therizinosaurs can be reasonably attributed to a shift from obligatory predation to a novel paleoecological role that reached its pinnacle in derived Late Cretaceous members.

Natural fracture distributions in sinuous, channel-fill sandstones of the Cedar Mountain Formation, Utah

A set of regional natural fractures, present in the sandy to conglomeratic, fluvial, channel-fill deposits of the Cedar Mountain Formation (east-central Utah) has a consistent west-northwest strike regardless of the local axial orientations of the sinuous channels. The fracture-producing stresses were not significantly refracted by the mechanical-property contrast between the channel-fill sandstones and the encasing overbank mudstones. In addition, fracture spacing along the sinuous channel axes is relatively constant between one-half and one-third of the bed thickness for both large fractures that cut the full thickness of the channel deposits and for smaller fractures in the thinner, component beds. Fracture spacing was apparently not affected by the variations in stress amplification that commonly result from differently oriented stiff inclusions in a ductile matrix. Therefore, in the absence of other structures, fracture intensity and the orientation of fracture-related maximum horizontal permeability in sinuous elongated reservoirs will be relatively constant regardless of the orientation of the long axis of the reservoir. Whether maximum permeability trends along, oblique, or across such reservoirs, and the relative drainage efficiency of horizontal versus vertical wellbores drilled into them, will vary only with the local trend of the channel axis.

Dalton Wells: Geology and significance of debris-flow-hosted dinosaur bonebeds in the Cedar Mountain Formation (Lower Cretaceous) of eastern Utah, USA

The Lower Cretaceous Dalton Wells dinosaur locality, north of Moab, Utah, consists of a 2 m thick, stacked succession of four fossil-rich bonebeds with an estimated collective lateral extent of more than 4000 m 2. To date, 215 m 2 of the bonebeds have been excavated and more than 4200 vertebrate fossil field specimens have been collected. The site occurs at the base of the Yellow Cat Member of the Cedar Mountain Formation, and lies unconformably on Upper Jurassic strata of the Morrison Formation. The age of the assemblage is tentatively accepted as Barremian. Nine dinosaur taxa are recognized, making Dalton Wells one of the richest (abundance and diversity) Lower Cretaceous dinosaur localities in the world. The bonebeds are rare examples of fossiliferous subaerial debris flow deposits. At least four flows originated an undetermined distance up-slope from an Early Cretaceous site of dinosaur bone concentration and flowed through the site carrying bones short distances toward an adjacent area of lakes, ponds and wetlands. Host sediments most likely accumulated on the eastward-dipping slopes of a backbulge in a foreland basin. The overall depositional setting was alluvial–lacustrine in a warm-to-hot and seasonally wet-and-dry climate. The consistent expression and location of lacustrine facies in both the Brushy Basin Member of the Morrison Formation and the Yellow Cat Member of the Cedar Mountain Formation indicate that high rates of subsidence typified the Dalton Wells area both before and after the J–K transition, and further suggest that there was some form of long-term to episodic and localized influence on subsidence. The depositional slope required to generate debris flows may have been established by forebulge crustal flexure, but could also have been established or amplified by the high rates of subsidence that maintained the lacustrine paleoenvironments in the field area. Concretionary deposits in the Yellow Cat Member at Dalton Wells are diagenetic and apparently resulted from groundwater precipitation, likely enhanced by the presence of organics (bones) and lacustrine carbonates. The regional and cross-facies expression of calcretes in the Yellow Cat Member combined with the rarity of pedogenic indicators confirms that they are not paleosols. Mineral precipitation likely occurred as groundwater flow was established in response to foreland basin development. It remains unknown under what specific circumstances animals died and carcasses accumulated prior to being reworked by debris flows. However, the stratigraphic association of seasonally wet-and-dry facies throughout the Yellow Cat Member suggests that drought-induced mortality events were probably common. In a seasonally wet-and-dry environment, debris flows may have been triggered by intense rainfall or seismic events.

A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah

Therizinosauroids are an enigmatic group of dinosaurs known mostly from the Cretaceous period of Asia, whose derived members are characterized by elongate necks, laterally expanded pelves, small, leaf-shaped teeth, edentulous rostra and mandibular symphyses that probably bore keratinized beaks. Although more than a dozen therizinosauroid taxa are known, their relationships within Dinosauria have remained controversial because of fragmentary remains and an unusual suite of characters. The recently discovered 'feathered' therizinosauroid Beipiaosaurus from the Early Cretaceous of China helped to clarify the theropod affinities of the group. However, Beipiaosaurus is also poorly represented. Here we describe a new, primitive therizinosauroid from an extensive paucispecific bonebed at the base of the Cedar Mountain Formation (Early Cretaceous) of east-central Utah. This new taxon represents the most complete and most basal therizinosauroid yet discovered. Phylogenetic analysis of coelurosaurian theropods incorporating this taxon places it at the base of the clade Therizinosauroiden, indicating that this species documents the earliest known stage in the poorly understood transition from carnivory to herbivory within Therizinosauroidea. The taxon provides the first documentation, to our knowledge, of therizinosauroids in North America during the Early Cretaceous.

Chapter 5: Marsupial Mammals from the Albian–Cenomanian (Early–Late Cretaceous) Boundary, Utah

The Mussentuchit local fauna, upper Cedar Mountain Formation (Cretaceous: Albian–Cenomanian), Utah, includes the geologically oldest marsupials: Kokopellia juddi, described previously, and three new taxa named herein. Adelodelphys muizoni, new genus and species, and Sinbadelphys schmidti, new genus and species, both unassignable to family, are among the smallest of Cretaceous marsupials; Pariadens mckennai, new species, tentatively assigned to Stagodontidae, is among the largest. The three are morphologically similar: they bear certain dental specializations of Marsupialia (e.g., presence of labial postcingulid and “twinning” of hypoconulid and entoconid on lower molars), but are plesiomorphic with respect to most or all Late Cretaceous marsupials in other features (e.g., relatively lingual position of conules, lack of stylar cusps C or D on upper molars). Compared to Late Cretaceous (Cenomanian– Maastrichtian) assemblages of North America, the marsupials of the Mussentuchit local fauna are rare and low in morphologic and taxonomic diversity. Biogeographic origin of Marsupialia and their antiquity in North America remain unknown. However, patterns of diversification and differentiation suggest that the taxa from the Cedar Mountain Formation lie near the base of North America's Cretaceous marsupial radiation.

Dinosaur Tracks from the Cedar Mountain Formation (Lower Cretaceous), Arches National Park, Utah

The seventh and largest known dinosaur tracksite from the Cedar Mountain Formation is reported from two important stratigraphic levels in the Ruby Ranch Member within the boundaries of Arches National Park. Previous reports of sites with a few isolated tracks are of limited utility in indicating the fauna represented by track makers. The Arches site reveals evidence of several theropod morphotypes, including a possible match for the coelurosaur Nedcolbertia and an apparently didactyl Utahraptor-like dromeosaurid. Sauropod tracks indicate a wide-gauge morphotype (cf. Brontopodus). Ornithischian tracks suggest the presence of an iguandontid-like ornithopod and a large ankylosaur. Dinosaur track diversity is high in comparison with other early Cretaceous vertebrate ichnofaunas, and it correlates well with faunal lists derived from skeletal remains, thus providing a convincing census of the known fauna.

A new teiid lizard from the Cedar Mountain Formation (Albian–Cenomanian boundary) of Utah

ABSTRACT A heretofore unknown teiid lizard, recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of Emery County, Utah, is the oldest teiid that is represented by numerous specimens. This new taxon has a heterodont dentition with conical anterior teeth and transversely oriented bicuspid posterior teeth that are distinct from those of Peneteius (Late Cretaceous) and Teius and Dicrodon (Recent). It also shows ontogenetic variation in tooth shape, in which the posterior teeth become more massive and have more transversely expanded crowns, as the individual grows older. Further comparisons and analysis indicate (1) that North American Cretaceous Polyglyphano-dontinae (characterized by teeth with transversely-oriented crests) achieved their unusual dental specializations independently from those of analogous modern taxa; (2) that their transverse tooth-cresting resulted from addition of a medial cusp (rather than crown rotation, as previously hypothesized and which apparently is the case for living taxa); and (3) that the species from the Cedar Mountain Formation represents a sister-taxon to other North American poly-glyphanodontines Polyglyphanodon, Peneteius and presumably Paraglyphanodon and Dicothodon. The new taxon thus represents an example of the morphologically antecedent dental specializations that culminated in the strikingly specialized dentition of Polyglyphanodon sternbergi.

Lizards of the Mussentuchit Local Fauna (Albian–Cenomanian boundary) and comments on the evolution of the Cretaceous lizard fauna of North America

ABSTRACT A diverse fauna of lizards has been recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of central Utah. These lizards are a component of the now recognized Mussentuchit local fauna and, like many of the other vertebrate groups within this fauna, show striking similarities to their North American Late Cretaceous (Campanian–Maastrichtian) counterparts. Unlike the Late Cretaceous lizard faunas, the lizards from the Mussentuchit local fauna also include at least one “paramacellodid,” a group common to Late Jurassic and Early Cretaceous lizard faunas of North America. Comparison with other Cretaceous lizard faunas from both North America and Asia indicates that the changes in the North American lizard fauna represented by the lizards of the Mussentuchit local fauna are likely the result of the introduction of taxa from Asia during the Early Cretaceous. Supposedly herbivorous taxa are found among the Polyglyphanodontine lizards from the Late Cretaceous of North American and Asia, but the general changes in the Cretaceous lizard fauna of North America cannot be convincingly shown to be linked to the concurrent angiosperm radiation. Later influxes of Asian lizard taxa prior to the Campanian may explain the relatively sudden appearance of additional groups of lizards in the early Campanian of North America. Whereas there is good evidence to support the hypothesis of an Asian influence on the Cretaceous lizard fauna of North America, there is insufficient evidence to determine what, if any, influence may have come from Europe or South America.

A new taxon of helodermatid-like lizard from the Albian–Cenomanian of Utah

ABSTRACT A new platynotan lizard, Primaderma nessovi, gen. et sp. nov., from the Mussentuchit Local Fauna, Cedar Mountain Formation (Albian–Cenomanian) of Utah is unique in having a premaxillary process of the maxilla that forms a vertical flange and fine serrations on anterior and posterior edges of the maxillary teeth. Primaderma is the oldest-known terrestrial platynotan and phylogenetic analysis indicates that it is a member of Monstersauria, a clade of helodermatid-like platynotans. The teeth of Primaderma show several derived platynotan characteristics, but do not possess venom grooves. The distribution of this trait in fossil taxa is reassessed. Although a North American origin of helodermatid-like platynotans is likely, it is possible that Primaderma represents another example of an Asian influence on the North American Cretaceous fauna. As with similar taxa, Primaderma was likely highly predaceous, presumably taking vertebrate prey and it appears that helodermatid-like lizards have changed very little since the Albian–Cenomanian.

New albanerpetontid amphibians from the albian to Coniacian of Utah, Usa—Bridging the gap

ABSTRACT Newly discovered fossils described herein from Utah, USA, help fill a sizeable gap in the Cretaceous record of the Albanerpetontidae and provide information on the evolution of the family during the latest Early–middle Late Cretaceous. The geologically oldest record of sympatry among albanerpetontids is in the Mussentuchit Member (latest Albian–earliest Cenomanian in age), Cedar Mountain Formation, where two indeterminate species are recognized based on jaws. The first species primitively resembles geologically older albanerpetontids in the structure of the premaxilla and documents the last appearance of this more primitive premaxillary pattern. The second species closely resembles the North American Campanian–Maastrichtian species Albanerpeton nexuosus in derived premaxillary features, and is the earliest record both of a subgeneric clade that includes all congeners, except A. arthridion, and of a less inclusive clade of Euramerican Upper Cretaceous–Miocene species having premaxillary synapomorphies that reinforced the snout. Albanerpeton cifellii, sp. nov. is named on a premaxilla having an inferred unique pattern of contact with the nasal. This new species is known only from the Smoky Hollow Member (late Turonian in age), Straight Cliffs Formation, and is the oldest member of a subgeneric clade of North American Upper Cretaceous species having a triangular or slit-shaped suprapalatal pit in the premaxilla. Indeterminate albanerpetontid bones are also reported from the above two units and the basal (early or middle Coniacian in age) John Henry Member, Straight Cliffs Formation.

Therian Teeth of Unusual Design from the Mid-Cretaceous (Albian–Cenomanian) Cedar Mountain Formation of Utah

Enigmatic, abundant mammalian teeth from the medial Cretaceous of Utah are shown to belong to antemolar loci, based on dentulous jaw fragments; isolated teeth representing several upper premolar loci and the reconstructed c-p4 series are identified. Three species, differing in size and morphology, can be recognized. Morphological appropriateness, relative abundance, and distributional data indicate that the teeth can be referred with some confidence to the three symmetrodonts known from the Cedar Mountain Formation: Spalacolestes cretulablatta, S. inconcinnus, and Spalacotheridium noblei. If the specimens represent replacement or successional teeth, they are strikingly atypical for Mesozoic mammals, particularly in their low crowns and high degree of molarization at posterior loci. Jaw structure, wear pattern, and aspects of tooth morphology (e.g., proportions, degree of molarization, enamel thickness) favor the alternative hypothesis that these teeth are deciduous. Diphyodonty at all antemolar loci is generally assumed to represent the primitive condition for mammals, though fossil evidence is scant; some of the earliest mammals are known to undergo replacement only at the last premolar locus, with ontogenetic loss (rather than replacement) mesially. Available evidence suggests that, like the eupantothere Dryolestes, North American spalacotheriid symmetrodonts probably underwent single replacement at most or all premolar loci and that the deciduous series became progressively more molariform distally, particularly at the p3–4 loci. Assuming that these teeth are deciduous, their great abundance in the Cedar Mountain Formation (and, apparently, elsewhere in the Cretaceous of North America) suggests that North American spalacotheriids were subject to unusually high juvenile mortality rates or, more probably, that succession at premolar loci took place late in ontogeny, compared to other Mesozoic mammals.

Upper Jurassic-Lower Cretaceous Morrison and Cedar Mountain formations, NE Utah-NW Colorado; relationships between nonmarine deposition and early Cordilleran foreland-basin development

ABSTRACT Sedimentologic, stratigraphic, and petrologic analysis of the Upper Jurassic-Lower Cretaceous Morrison and Cedar Mountain formations of Utah and Colorado provides information on the timing and nature of early Cordilleran foreland-basin development. The Morrison Formation can be subdivided into three depositional facies assemblages: (1) lower progradational shallow marine, lacustrine, fluvial, and eolian facies deposited during Oxfordian-Kimmeridgian retreat of the Stump-Sundance sea; (2) a middle assemblage containing sandy-gravelly braided fluvial deposits, which are overlain by meandering fluvial channel and overbank facies; and (3) an upper assemblage of laterally stable, low-sinuosity, fluvial channel facies deposited during Tithonian-early Neocomian (?) time. The upper part of this assemblage shows evidence of alteration and early diagenesis related to development of an Early Cretaceous unconformity. The overlying Cedar Mountain Formation is subdivided into two facies assemblages: (1) the Neocomian Buckhorn Conglomerate was deposited by northeast-trending, sandy-gravelly braided rivers that were incised into the underlying Morrison Formation; (2) an upper assemblage containing laterally stable, low-sinuosity, fluvial channel facies deposited during late Neocomian-Albian time. The base of the unit contains a thick calcrete zone that formed during an unconformity following Buckhorn deposition. Morrison and Cedar Mountain formation sandstones contain three petrofacies: a feldspar-rich lower Morrison petrofacies (%QmFLt = 70, 19, 11), and chert-rich upper Morrison and Buckhorn/Cedar Mountain petrofacies (%QmFLt = 54, 5, 41 and 69, 4, 27, respectively). Sandstone composition and paleocurrent data indicate a Cordilleran source area composed of Proterozoic, Paleozoic, and Mesozoic sedimentary rocks. The Morrison Formation and Buckhorn Conglomerate were deposited in the back-bulge depozone of the Late Jurassic Cordilleran foreland-basin system and onlapped a flexural forebulge located in central Utah. Late Neocomian eastward migration of the forebulge uplifted areas in eastern Utah, producing an unconformity, while the foredeep in central Utah underwent flexural subsidence. The upper part of the Cedar Mountain Formation represents overfilling of the foredeep and deposition above the forebulge.

Triconodont mammals from the medial Cretaceous of Utah

ABSTRACT Herein we describe triconodontid mammals from the upper part of the Cedar Mountain Formation (placed approximately at the Albian–Cenomanian, or Lower–Upper Cretaceous, boundary), Emery County, Utah. Three new species, based on dentulous jaw fragments and isolated teeth, are included; one is referred to Astroconodon, one to Corviconodon (both previously recorded from the Aptian–Albian), and one to a new genus. This diversity is comparable to that seen in the Aptian–Albian Cloverly Formation, and differs from succeeding faunas of the North American Cretaceous, in which triconodontids are rare or lacking altogether. The species differ greatly in size; the largest, at an estimated body weight of 750 g, is the largest known triconodontid and presumably incorporated vertebrate prey into its diet. Triconodont relationships are problematic. Craniodental evidence supports a monophyletic Triconodontidae, and there is weak support for a monophyletic grouping of the North American Cretaceous taxa within the family. However, an exclusive common ancestry for North American Cretaceous triconodontids cannot be readily identified among the morphological diversity known for Late Jurassic taxa. Instead, limited evidence at hand suggests that Late Jurassic Triconodontidae (Triconodon, Priacodon, Trioracodon) form a monophyletic group.