Cretaceous Cloverly Formation Research Articles

Skeletal variation of the stem turtle Naomichelys speciosa (Testudinata: Helochelydridae): insights from a new specimen from the Lower Cretaceous Cloverly Formation of Montana

Specimens of Naomichelys speciosa are typically represented by fragmentary shell elements that offer little morphological information beyond surface ornamentation, and only a single mostly complete specimen has been described in detail. Here, we describe a second relatively complete specimen of N. speciosa from the Cloverly Formation of Montana. This specimen provides new information on the morphology of damaged or missing skeletal elements from previously described specimens including costal I, the peripheral series, plastral bridge, cervical vertebrae, and femur. New diagnostic features of N. speciosa include the presence of supernumerary pleural scutes on costal I, the absence of intergular scutes, and the variable presence of central plastral fontanelle. Additionally, this specimen offers insight into intraspecific variation within N. speciosa such as, the presence/absence of the central plastral fontanelle and the relative size/shape of the entoplastron and entoplastral scute.

Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), III: a new species of Albanerpeton, with biogeographic and paleoecological implications

ABSTRACT We describe a new species of the albanerpetontid amphibian Albanerpeton from three localities in the Lower Cretaceous Cloverly Formation of Wyoming, U.S.A. Radiometric dates between ∼111–112 Ma indicate it is slightly younger than A. arthridion from the Antlers Formation. The new species is diagnosed on a pair of fused frontals that possess a unique combination of characters, mixing plesiomorphic features of the internasal process with a more derived overall shape and proportions. Referred material includes premaxillae, maxillae, dentaries, atlantes, ‘axes,’ trunk vertebrae, humeri, and an ilium. Phylogenetic analyses place the new species near the base of Albanerpeton sensu lato but without fully resolving its position. The inclusion of Shirerpeton and Wesserpeton within this clade opens up the possibility that these genera might be incorporated into Albanerpeton, or that a number of species formerly assigned to Albanerpeton might receive new generic assignments. By including several informal species in our analysis, it becomes clear that character distributions are more homoplastic and that past genus typologies are probably less secure. We assign the new species to Albanerpeton conservatively, pending further phylogenetic study. The Cloverly Albanerpeton is found in unambiguously aquatic deposits, suggesting that the animal lived near these settings for at least part of its life. This is a common habitat for Mesozoic albanerpetontids, unlike the karst-dominated, often drier, deposits in which Cenozoic species are typically found. Despite the recent discovery of a probable arboreal species, it is likely that albanerpetontids inhabited a range of habitats throughout their evolutionary history.

Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), II: Paleoecology

ABSTRACTVertebrate microfossil assemblages in terrestrial formations are a promising source of data on the structure of fossil metacommunities. However, the degree to which these deposits capture true, metacommunity-level samples is unknown. Individual deposits may be biased in ways that limit their utility for intra- and inter-formation comparisons. This study describes the composition of ten vertebrate microfossil assemblages collected from the Lower Cretaceous Cloverly Formation in Montana and Wyoming, U.S.A., and evaluates whether the assemblages are sufficiently similar to suggest the presence of a single Cloverly metacommunity, or ‘paleocommunity type.’ The assemblages appear to be biased by factors related to the preferential incorporation and preservation of different taxa and skeletal element types, which compound with decreasing locality sample size. Less productive localities lack whole taxonomic groups, especially small, fully terrestrial vertebrates. Only the two vertebrate microfossil bonebeds approach the known formation richness. High individual tooth counts overrepresent particular species, especially the crocodylians. Despite these biases, the multiple assemblages nevertheless yield statistically similar taxon abundance rank orders, suggesting the presence of a single, formation-wide paleo-metacommunity, which bears resemblance to a viable metacommunity. The aggregate assemblage exhibits an ‘Eltonian pyramid’ trophic hierarchy for both terrestrial and aquatic taxa. Comparing the multiple assemblages synoptically also reveals possible landscape-scale abundance patterns for particular species. Taken together, microvertebrate assemblages offer insight into regional paleo-metacommunities and provide samples for inter-formational comparisons at this level.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Carrano, M. T., M. P. J. Oreska, and R. Lockwood. 2016. Vertebrate paleontology of the Cloverly Formation (Lower Cretaceous), II: Paleoecology. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1071265.

Tribosphenic mammals from the Lower Cretaceous Cloverly Formation of Montana and Wyoming

ABSTRACTWe report a diverse assemblage of tribosphenidan mammals from several localities in the Cloverly Formation (Lower Cretaceous, Albian) of Montana and Wyoming. This unit is of historical significance for yielding well-known dinosaurs (e.g., Deinonychus antirrhopus, Tenontosaurus tilletti) and early mammals (e.g., Gobiconodon ostromi, Montanalestes keeblerorum). We provisionally identify 13 taxa (five of which are formally recognized), including Pappotherium pattersoni, a new species of the deltatheroidan Oklatheridium (O. wiblei, sp. nov.), a eutherian (Montanalestes, previously named), and two new basal tribosphenidans (Argaliatherium robustum, gen. et sp. nov., and Carinalestes murensis, gen. et sp. nov.). An unnamed taxon, represented by associated but almost edentulous dentaries, is interpreted to have had four incisors, a single-rooted canine, three premolars, and four molars, indicating that the metatherian tooth formula was established by the Albian. In addition, an indeterminate lower molar fragment preserving twinned talonid cusps and a buccal postcingulid provides the earliest evidence for Marsupialiformes. We also provide a more detailed description of the associated dentaries (holotype) of Montanalestes keeblerorum. The mammalian fauna from the Cloverly Formation shares several taxa with the roughly contemporaneous Trinity Group of Oklahoma and Texas, an observation that also applies to the dinosaur fauna, suggesting some degree of latitudinal homogeneity among described terrestrial vertebrates in this part of the North American Early Cretaceous.http://zoobank.org/urn:lsid:zoobank.org:pub:F62E498B-9E95-475B-B2E3-0CA6FC31FB2A

The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming

ABSTRACT We redescribe and present newly excavated sauropod material from the Lower Cretaceous Cloverly Formation of Wyoming that we refer to the titanosauriform Sauroposeidon proteles. In contrast to previous hypotheses that it was a brachiosaurid, we assert that Sauroposeidon is a member of the Somphospondyli on the basis of numerous features. Thus, the mid-Cretaceous disappearance of sauropods from the North American fossil record concerned both brachiosaurids and somphospondylans. We find claims for titanosaurs in the Early Cretaceous of North America to be unsubstantiated. The latest register of Sauroposeidon and other Early Cretaceous North American sauropods (before the ‘sauropod hiatus’) occurs in or below the coastal units marking transgression of the Western Interior Seaway, whereas many ecologically disparate dinosaur groups are present both below and above this boundary in the same geologic units that sauropods are found in. The presence of these through-ranging groups with sauropods before and after sauropod absence suggests that appropriate sauropod-bearing environments were present into the Late Cretaceous, implying that the disappearance of sauropods is not attributable to taphonomic or sampling bias. Furthermore, field observations of the Cloverly Formation indicate that Cretaceous pre-hiatus sauropods inhabited near-coastal environments, which were abundant in the western United States well after the start of the hiatus. The start of the sauropod hiatus is interpreted as the result of a genuine continent-wide extinction, coincident with the appearance of (and perhaps attributable to competition with) advanced ornithischian herbivores, decrease in habitat due to the incursion of the Western Interior Seaway, or both.

A new titanosauriform from the Early Cretaceous Cloverly Formation of Montana

New material representing the northernmost titanosauriform from North America is described from the Cloverly Formation (Aptian/Albian) of Montana, USA. Representing a basal titanosauriform, Rugocaudia cooneyi gen. et sp. nov., the remains consist of 18 caudal vertebral and associated material. Possessing a combination of several unique caudal vertebrae features, Rugocaudia appears uniquely distinct from previously recognized North American sauropod genera. This Early Cretaceous taxon from Montana and subsequent discovery of titanosauriform material from Wyoming indicates a stronger Early Cretaceous sauropod presence across the continental USA than previously recognized. The presence of these northern latitude taxa helps to expand the spatial distribution of Early Cretaceous sauropods and is an additional piece of evidence to counter the claims of waning Early Cretaceous sauropod diversity in North America.

A new ankylosaur (Dinosauria: Ankylosauria) from the Lower Cretaceous Cloverly Formation of central Montana

A cranium and other associated skeletal elements representing a new ankylosaurid dinosaur, Tatankacephalus cooneyorum gen. et sp. nov. possess several diagnostic features that indicate that this new taxon differs from the only other known ankylosaur from the Cloverly Formation, Sauropelta edwardsorum . These features include a frontoparietal dome, an enlarged nuchal ridge that obscures the occipital region, a circular orbit, ventral curvature in the posterolaterally directed paroccipital processes, a posteroventrally directed foramen magnum, and a number of features on the braincase. The phylogenetic analysis positions Tatankacephalus with Ankylosauridae based on its sharing of several characters with other members of this clade, including an enlarged nuchal segment that obscures the occiput in dorsal view, a ventrally curving lateral profile of the cranium anterior to the orbit, pyramidal postorbital boss, laterally projecting pyramidal quadratojugal boss, the presence of a postocular shelf, the presence of paranasal sinuses, and the lack of a cingulum on a maxillary (or dentary) tooth. It is considered a basal member of Ankylosauridae because it retains premaxillary teeth and a visible lateral temporal fenestra, in contrast to the absence of premaxillary teeth and an obscured lateral temporal fenestra in younger members of this clade.

Gobiconodonts from the Early Cretaceous of Oshih (Ashile), Mongolia

We describe here the first discovered mammalian remains from the Mongolian Early Cretaceous locality Oshih (Ashile). Four fragmentary, tooth-bearing specimens, probably corresponding to three individuals, have been recovered. All the fossils can be assigned to the family Gobiconodontidae (Chow and Rich, 1984). The specimens include three lower jaw fragments and one upper jaw fragment, and represent at least two different taxa.Gobiconodon hopsoni n. sp., is described and diagnosed here. This new species is larger than G. ostromi (Early Cretaceous Cloverly Formation, USA); thus, it is the largest triconodont and one of the largest Mesozoic mammals known. Gobiconodon sp., found also at Oshih, is slightly larger than G. borissiaki from the Early Cretaceous of Khoobur, Mongolia, but smaller than G. ostromi The specimens of this second species are poorly preserved and provide insufficient data for a diagnosis.The status of the different species of Gobiconodon and the new gobiconodontid Hangjinia is reviewed. In gobiconodontids and Triconodontidae, the maxillae appear to make a significant contribution to the orbital rim, a condition unusual among basal mammals, in which the lacrimal and jugal are the main components. Other triconodonts such as Jeholodens likely an “amphilestid”, appear to show the primitive mammalian condition for this feature. We present a brief consideration of triconodont relationships and discuss alternative placements of Gobiconodon among Mammaliaformes.

Sauroposeidon proteles, a new sauropod from the early Cretaceous of Oklahoma

ABSTRACT Sauroposeidon proteles, a new brachiosaurid sauropod, is represented by an articulated series of four mid-cervical vertebrae recovered from the Antlers Formation (Aptian–Albian) of southeastern Oklahoma. Most Early Cretaceous North American sauropod material has been referred to Pleurocoelus, a genus which is largely represented by juvenile material and is not well understood. Regardless of the status and affinities of Pleurocoelus, the new taxon is morphologically and proportionally distinct. Among well-known sauropod taxa, Sauroposeidon is most similar to Brachiosaurus; particularly noteworthy are the neural spines, which are set forward on the centra and are not bifurcate, and the extremely elongate cervical ribs. Sauroposeidon and Brachiosaurus also share a derived pattern of pneumatic vertebral ultrastructure and a mid-cervical transition point, at which neural spine morphology changes from very low (anteriorly) to very high (posteriorly). Autapomorphies of Sauroposeidon include posterior placement of the di apophyses, hypertrophied pneumatic fossae in the lateral faces of the neural spines and centra, and an extraordinary degree of vertebral elongation (e.g., C8 = 1.25 m; 25% longer than Brachiosaurus). Additional sauropod material from the Early Cretaceous Cloverly Formation may be referrable to the new Oklahoma sauropod, which appears to be the last of the giant North American sauropods and represents the culmination of brachiosaurid trends towards lengthening and lightening of the neck.

Abstract: Origin and Distribution of Organic Matter in Mudstones of the Lower Cretaceous Cloverly Formation of Wyoming

Abstract: Origin and Distribution of Organic Matter in Mudstones of the Lower Cretaceous Cloverly Formation of Wyoming

Skeletal reconstruction and life restoration of Sauropelta (Ankylosauria: Nodosauridae) from the Cretaceous of North America

A skeletal reconstruction and life restoration are presented for the Early Cretaceous nodosaurid ankylosaur Sauropelta edwardsi. This composite is based on several partial skeletons having armor preserved in situ from the Lower Cretaceous Cloverly Formation of Wyoming and Montana. Comparison of foot morphology with that of the ichnofossil Tetrapodosaurus borealis, from the Lower Cretaceous Gething Formation of British Columbia, suggests that the footprint is that of Sauropelta. A hypothesis is presented suggesting that most ankylosaurs are found on their backs because of bloating.

A new triconodontan (Mammalia) from the Jurassic of China

ABSTRACT Klamelia zhaopengi gen. et sp. nov., a new triconodontan from the Middle or Late Jurassic of northwestern China, has close affinities with Gobiconodon borissiaki Trofimov, 1978, and Guchinodon hoburensis Trofimov, 1978, from the Early Cretaceous of Mongolia. All three species are characterised by a foreshortened anterior region of the mandible and a reduced number of antemolars as compared with all other amphilestid triconodontans. They are therefore here united as the new subfamily Gobiconodontinae. Another member of the Gobiconodontinae may be an undescribed amphilestid from the Early Cretaceous Cloverly Formation of Montana, U.S.A. If so, the presently known geographic and stratigraphic distribution of these forms suggests they were confined to the Middle or Late Jurassic and Early Cretaceous of eastern Asia and western North America.

Petrology and Stratigraphy of Nonmarine Upper Jurassic-Lower Cretaceous Rocks of Western Wyoming and Southeastern Idaho

The Nevadan orogeny had little influence on sedimentation along the eastern margin of the Cordilleran geosyncline in the Late Jurassic Epoch. Montmorillonite in the Morrison, upper Ephraim, and Cloverly formations is believed to be an alteration product of volcanic ash blown from volcanic centers in western California and Oregon during the Late Jurassic, and from sources farther north during the Early Cretaceous. Thus the presence of such ash indirectly reflects tectonism in the present western Cordillera, but the first changes in physical sedimentation that can be related directly to the Cordilleran orogeny occurred in western Wyoming in Early Cretaceous time, as shown by study of Gannett and Cloverly rocks. Petrologic similarities, especially of feldspar and chert content, between the Morrison Formation in central Wyoming and lower Ephraim formation in the Wyoming-Idaho thrust belt suggest that they were derived from the same sources and probably are time equivalent, if considered within the Late Jurassic tectonic setting. The Wyoming interior basin was stable during Late Jurassic time, and one source of sediment was on the southwest in western Utah and northern Arizona. Sediment was carried northeastward by prograding streams as the Sundance Sea retreated north. Abrupt coarsening and influx of phosphorite and spicular chert detritus at the base of the Cretaceous Cloverly Formation and basal conglomerate of the upper Ephraim formation suggest that a change in provenance accompanied tectonic disturbances. Limestone clasts in the conglomerates came from the Pennsylvanian and Permian rocks of Idaho and northern Nevada. This fact and concurrent textural coarsening suggest that the basal Cloverly is largely time equivalent to the lowest widespread conglomerate in the Ephraim. Regional maps show that the Cloverly and equivalent formations both thicken and coarsen westward. As a result of Early Cretaceous uplift, sediments composed predominantly of chert and carbonate were shed eastward to form a clastic wedge deposit in the western Wyoming basin. Unlike some better known clastic wedges (e.g., Catskill Formation), this one contains little feldspar and few igneous and metamorphic rock fragments.