Lower Cretaceous Cloverly 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.

Ontogenetic dietary shifts in Deinonychus antirrhopus (Theropoda; Dromaeosauridae): Insights into the ecology and social behavior of raptorial dinosaurs through stable isotope analysis

The image of the highly intelligent, pack-hunting raptor has become engrained in scientific literature and popular works alike. First proposed to explain the relatively common co-occurrence of the large-bodied iguanodontian Tenontosaurus tilletti and the wolf-sized Deinonychus antirrhopus from the Lower Cretaceous of North America, a canid-like social hunting structure has become the standard depiction of dromaeosaurs in popular works over the last three decades. This reconstruction is, however, problematic largely due to the fact that highly coordinated hunting strategies are rarely observed in modern archosaurs. This has led to the alternative hypothesis that D. antirrhopus was more analogous to agonistic reptilian carnivores, like the Komodo dragon (Varanus komodoensis). Among the many differences between these two analogs is how social and asocial organisms rear their young, producing a diagnostic pattern based on the presence or absence of ontogenetic dietary changes. In order to test for dietary changes through growth, stable carbon and oxygen isotope (δ13C, δ18O) analysis was performed on tooth carbonate from small (<4.5 mm crown height) and large (>9 mm crown height) D. antirrhopus specimens from two microsites from the Lower Cretaceous Cloverly (Montana) and Antlers (Oklahoma) formations. Teeth from goniopholidid crocodylians and Tenontosaurus tilletti from the Cloverly Formation were also tested for comparison. The results show that the Cloverly goniopholidids, like their modern counterparts, went through a distinct transition in diet as they grew. The smallest teeth were the relatively most enriched in 13C (mean = −9.32‰; n = 5), the medium-sized teeth were the most-depleted in 13C (mean = −10.56‰; n = 5), and the largest teeth were intermediate (mean = −10.12‰; n = 6). These factors are characteristic of the dietary shifts seen in modern asocial reptiles. D. antirrhopus showed this same pattern in tooth samples collected from both rock units, with small teeth being the more enriched in 13C (mean = −8.99‰; n = 10) and the large teeth being more depleted in 13C (mean = −10.38‰; n = 10). These differences suggest that juvenile and adult D. antirrhopus from both formations likely consumed different prey. Hypothetical food sources, such as T. tilletti, are close to the 13C isotopic signal of adult D. antirrhopus, consistent with the hypothesized trophic relationship (predator-prey) between these two species. Juvenile D. antirrhopus had a diet more enriched in 13C, likely composed of smaller-bodied, but trophically-higher species. Taken together, these data add to the growing evidence that D. antirrhopus was not a complex social hunter by modern mammalian standards.

First occurrence of the boreal fossil wood Xenoxylon meisteri from the Jurassic of North America: Morrison Formation of central Montana, USA

Six specimens of the fossil wood Xenoxylon meisteri were discovered in the Upper Jurassic Morrison Formation of central Montana and are described herein. The discovery represents the first confirmed occurrence of the species X. meisteri in North America. In addition, we review all occurrences of petrified wood attributed to Xenoxylon from North America. Early to Late Jurassic X. phyllocladoides specimens of Greenland are accepted. Previously reported occurrences of Xenoxylon from the Lower Jurassic Navajo Sandstone of Utah, Xenoxylon morrisonense Medlyn and X. moorei Tidwell from the Upper Jurassic Morrison Formation of Utah, and fossil woods reported from the Lower Cretaceous Cloverly (Wyoming) and McMurray Sandstone (Alberta, Canada) formations have secondary xylem characteristics incongruous with the genus and are discounted. The remaining accepted specimens are Cretaceous in age from the Canadian Arctic (Valanginian) and the North Slope of Alaska (Albian and Maastrichtian). Thus, these new Montana specimens of Xenoxylon are the earliest and southernmost occurrences of the genus in continental North America. Global distribution and paleoecology strongly imply Xenoxylon was constrained to cool/wet climates. Thus, these lower latitude North American occurrences corroborate other proxies indicating a cooler wetter climate, at least locally/briefly, in the northern portion of the Upper Jurassic Morrison foreland basin.

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 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.

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.

Stratigraphy of Upper Jurassic Morrison and Lower Cretaceous Cloverly Formations of Big Horn Basin, Northern Wyoming: ABSTRACT

The Morrison and Cloverly Formations in the Big Horn basin of northern Wyoming and southern Montana are part of a distal edge of a westward-thickening clastic wedge of sediments deposited in an elongate intracontinental basin in the western North American craton. These formations reflect orogenic and volcanic activity in the western Cordillera during Late Jurassic and the subsequent eastward migration of volcanic centers during Early Cretaceous. The Morrison Formation (Upper Jurassic) conformably overlies the Jurassic marine Sundance Formation and consists of light olive-green, lenticular, calcareous siltstones and mudstones interbedded with white to buff or yellowish green, massive and cross laminated, calcareous quartzarenites. The olive-green mudstones in the upper portion of the formation alternate with red-brown calcareous mudstones or shales producing red banding. A lenticular bed of siliceous accretionary lapilli is present in the upper portion of the formation along the west flank of Sheep Mountain anticline, north of Greybull, suggesting a closer proximity to volcanic vents than previously hypothesized. The Cloverly Formation (Lower Cretaceous) consists of three members: the Pryor Conglomerate, the Little Sheep Mudstone, and the Himes; it overlies the Morrison Formation both conformably and unconformably. Its basal contact is sometimes marked by a lenticular, cross-bedded, conglomeratic quartzarenite or a pebble conglomerate consisting of clasts of black chert (Pryor Conglomerate) derived from uplifted Paleozoic deposits to the west and deposited as channel lag. The Little Sheep Mudstone Member is composed of variegated mudstones which are generally noncalcareous bentonitic, and laced with abundant chalcedony and barite concretions and veinlets. The Himes Member also contains a stacked sequence of devitrified tuffs interbedded with bentonitic mudstones, which locally may be several m ters thick. The individual tuffs, however, are generally less than 1 m (3 ft) thick and are very fine grained, buff to white, and massive. Also, relatively thin lenticular lithic wackes occur in the Himes Member. These are anomalous to the quartzarenites of the rest of the Morrison and Cloverly. A thick lenticular, trough-cross-bedded, quartzarenite caps the formation. Both the Morrison and Cloverly Formations are characterized by high ratios of overbank fines relative to coarse channel sands. It has been assumed, but not documented by detailed sedimentologic study, that the deposits were part of an aggrading alluvial flood plain complex dotted by seasonal lakes and swamps and crossed by braided rivers. This model deviates from most modern braided systems which are characterized by rapid lateral mobility and the lack of fine-grained overbank material. The large ratio of fine-grained siltstones and mudstones to coarser grained sandstones can be explained by a number of processes, the most probable being rapid overbank aggradation as a result of a large influx of wind-blown volcanic material from vents to the west. However, this ratio could also be ob ained in a rapidly subsiding basin whose river systems are characterized by long periods between avulsion, which is common in an arid to semiarid environment. End_of_Article - Last_Page 1346------------