Braincase anatomy of Almadasuchus figarii (Archosauria,Crocodylomorpha) and a review of the cranial pneumaticity in the origins of Crocodylomorpha

Almadasuchus figarii is a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remains. The skull of the only specimen of the monotypic Almadasuchus was restudied using high-resolution computed micro tomography. Almadasuchus has an apomorphic condition in its skull shared with the closest relatives of crocodyliforms (i.e. hallopodids) where the quadrates are sutured to the laterosphenoids and the otoccipital contacts the quadrate posterolaterally, reorganizing the exit of several cranial nerves (e.g. vagus foramen) and the entry of blood vessels (e.g. internal carotids) on the occipital surface of the skull. The endocast is tubular, as previously reported in thalattosuchians, but has a marked posterior step, and a strongly projected floccular recess as in other basal crocodylomorphs. Internally, the skull of Almadasuchus is heavily pneumatized, where different air cavities invade the bones of the suspensorium and braincase, both on its dorsal or ventral parts. Almadasuchus has a large basioccipital recess, which is formed by cavities that excavate the basioccipital and the posterior surface of the basisphenoid, and unlike other crocodylomorphs is connected with the basisphenoid pneumatizations. Ventral to the otic capsule, a pneumatic cavity surrounded by the otoccipital and basisphenoid is identified as the rhomboidal recess. The quadrate of Almadasuchus is highly pneumatized, being completely hollow, and the dorsal pneumatizations of the braincase are formed by the mastoid and facial antra, and a laterosphenoid cavity (trigeminal diverticulum). To better understand the origins of pneumatic features in living crocodylomorphs we studied cranial pneumaticity in the basal members of Crocodylomorpha and found that: (a) prootic pneumaticity may be a synapomorphy for the whole clade; (b) basisphenoid pneumaticity (pre-, postcarotid and rostral recesses) is a derived feature among basal crocodylomorphs; (c) quadrate pneumatization is acquired later in the history of the group; and (d) the rhomboidal sinus is a shared derived trait of hallopodids and crocodyliforms. The marine thallatosuchians exhibit a reduction of the pneumaticity of the braincase and this reduction is evaluated considering the two phylogenetic positions proposed for the clade.     

Vertebral pneumaticity is correlated with serial variation in vertebral shape in storks

Birds and their ornithodiran ancestors are unique among vertebrates in exhibiting air-filled sinuses in their postcranial bones, a phenomenon called postcranial skeletal pneumaticity. The factors that account for serial and interspecific variation in postcranial skeletal pneumaticity are poorly understood, although body size, ecology, and bone biomechanics have all been implicated as influencing the extent to which pneumatizing epithelia invade the skeleton and induce bone resorption. Here, I use high-resolution computed-tomography to holistically quantify vertebral pneumaticity in members of the neognath family Ciconiidae (storks), with pneumaticity measured as the relative volume of internal air space. These data are used to describe serial variation in extent of pneumaticity and to assess whether and how pneumaticity varies with the size and shape of a vertebra. Pneumaticity increases dramatically from the middle of the neck onwards, contrary to previous predictions that cervical pneumaticity should decrease toward the thorax to maintain structural integrity as the mass and bending moments of the neck increase. Although the largest vertebrae sampled are also the most pneumatic, vertebral size cannot on its own account for serial or interspecific variation in extent of pneumaticity. Vertebral shape, as quantified by three-dimensional geometric morphometrics, is found to be significantly correlated with extent of pneumaticity, with elongate vertebrae being less pneumatic than craniocaudally short and dorsoventrally tall vertebrae. Considered together, the results of this study are consistent with the hypothesis that shape- and position-specific biomechanics influence the amount of bone loss that can be safely tolerated. These results have potentially important implications for the evolution of vertebral morphology in birds and their extinct relatives.     

Postcranial Pneumaticity and Bone Structure in Two Clades of Neognath Birds

Most living birds exhibit some degree of postcranial skeletal pneumaticity, aeration of the postcranial skeleton by pulmonary air sacs and/or directly from the lungs. The extent of pneumaticity varies greatly, ranging from taxa that are completely apneumatic to those with air filling most of the postcranial skeleton. This study examined the influence of skeletal pneumatization on bone structural parameters in a sample of two size‐ and foraging‐style diverse (e.g., subsurface diving vs. soaring specialists) clades of neognath birds (charadriiforms and pelecaniforms). Cortical bone thickness and trabecular bone volume fraction were assessed in one cervical and one thoracic vertebra in each of three pelecaniform and four charadriiform species. Results for pelecaniforms indicate that specialized subsurface dive foragers (e.g., the apneumatic anhinga) have thicker cortical bone and a higher trabecular bone volume fraction than their non‐diving clademates. Conversely, the large‐bodied, extremely pneumatic brown pelican (Pelecanus occidentalis) exhibits thinner cortical bone and a lower trabecular bone volume fraction. Such patterns in bone structural parameters are here interpreted to pertain to decreased buoyancy in birds specialized in subsurface dive foraging and decreased skeletal density (at the whole bone level) in birds of larger body size. The potential to differentially pneumatize the postcranial skeleton and alter bone structure may have played a role in relaxing constraints on body size evolution and/or habitat exploitation during the course of avian evolution. Notably, similar patterns were not observed within the equally diverse charadriiforms, suggesting that the relationship between pneumaticity and bone structure is variable among different clades of neognath birds. Anat Rec, 296:867–876, 2013. © 2013 Wiley Periodicals, Inc.     

The morphology and evolution of chondrichthyan cranial muscles: A digital dissection of the elephantfish Callorhinchus milii and the catshark Scyliorhinus canicula

The anatomy of sharks, rays, and chimaeras (chondrichthyans) is crucial to understanding the evolution of the cranial system in vertebrates due to their position as the sister group to bony fishes (osteichthyans). Strikingly different arrangements of the head in the two constituent chondrichthyan groups—holocephalans and elasmobranchs—have played a pivotal role in the formation of evolutionary hypotheses targeting major cranial structures such as the jaws and pharynx. However, despite the advent of digital dissections as a means of easily visualizing and sharing the results of anatomical studies in three dimensions, information on the musculoskeletal systems of the chondrichthyan head remains largely limited to traditional accounts, many of which are at least a century old. Here, we use synchrotron tomographic data to carry out a digital dissection of a holocephalan and an elasmobranch widely used as model species: the elephantfish, Callorhinchus milii, and the small-spotted catshark, Scyliorhinus canicula. We describe and figure the skeletal anatomy of the head, labial, mandibular, hyoid, and branchial cartilages in both taxa as well as the muscles of the head and pharynx. In Callorhinchus, we make several new observations regarding the branchial musculature, revealing several previously unreported or ambiguously characterized muscles, likely homologous to their counterparts in the elasmobranch pharynx. We also identify a previously unreported structure linking the pharyngohyal of Callorhinchus to the neurocranium. Finally, we review what is known about the evolution of chondrichthyan cranial muscles from their fossil record and discuss the implications for muscle homology and evolution, broadly concluding that the holocephalan pharynx is likely derived from a more elasmobranch-like form which is plesiomorphic for the chondrichthyan crown group. This dataset has great potential as a resource, particularly for researchers using these model species for zoological research, functional morphologists requiring models of musculature and skeletons, as well as for palaeontologists seeking comparative models for extinct taxa.     

The Braincase and Neurosensory Anatomy of an Early Jurassic Marine Crocodylomorph: Implications for Crocodylian Sinus Evolution and Sensory Transitions

Modern crocodylians are a morphologically conservative group, but extinct relatives (crocodylomorphs) experimented with a wide range of diets, behaviors, and body sizes. Among the most unusual of these fossil groups is the thalattosuchians, an assemblage of marine‐dwellers that transitioned from semiaquatic species (teleosaurids and kin) into purely open‐ocean forms (metriorhynchids) during the Jurassic and Cretaceous Periods (ca 191–125 million years ago). Thalattosuchians can give insight into the origin of modern crocodylian morphologies and how anatomy and behavior change during a major evolutionary transition into a new habitat. Little is known, however, about their brains, sensory systems, cranial sinuses, and vasculature. We here describe the endocranial anatomy of a well‐preserved specimen of the Jurassic semiaquatic teleosaurid Steneosaurus cf. gracilirostris using X‐ray micro‐CT. We find that this teleosaurid still had an ear well attuned to hear on land, but had developed large internal carotid and orbital arteries that likely supplied salt glands, previously thought to be present in only the fully pelagic metriorhynchids. There is no great gulf in endocranial anatomy between this teleosaurid and the metriorhynchids, and some of the features that later permitted metriorhynchids to invade the oceanic realm were apparently first developed in semiaquatic taxa. Compared to modern crocodylians, Steneosaurus cf. gracilirostris has a more limited set of pharyngotympanic sinuses, but it is unclear whether this relates to its aquatic habitat or represents the primitive condition of crocodylomorphs that was later elaborated. Anat Rec, 299:1511–1530, 2016. © 2016 Wiley Periodicals, Inc.     

Cranial biomechanics,bite force and function of the endocranial sinuses in Diprotodon optatum,the largest known marsupial

The giant extinct marsupial Diprotodon optatum has unusual skull morphology for an animal of its size, consisting of very thin bone and large cranial sinuses that occupy most of the internal cranial space. The function of these sinuses is unknown as there are no living marsupial analogues. The finite element method was applied to identify areas of high and low stress, and estimate the bite force of Diprotodon to test hypotheses on the function of the extensive cranial sinuses. Detailed three‐dimensional models of the cranium, mandible and jaw adductor muscles were produced. In addition, manipulations to the Diprotodon cranial model were performed to investigate changes in skull and sinus structure, including a model with no sinuses (sinuses ‘filled’ with bone) and a model with a midsagittal crest. Results indicate that the cranial sinuses in Diprotodon significantly lighten the skull while still providing structural support, a high bite force and low stress, indicating the cranium may have been able to withstand higher loads than those generated during feeding. Data from this study support the hypothesis that pneumatisation is driven by biomechanical loads and occurs in areas of low stress. The presence of sinuses is likely to be a byproduct of the separation of the outer surface of the skull from the braincase due to the demands of soft tissue including the brain and the large jaw adductor musculature, especially the temporalis. In very large species, such as Diprotodon, this separation is more pronounced, resulting in extensive cranial sinuses due to a relatively small brain compared with the size of the skull.     

Histology and pneumaticity of Aoniraptor libertatem (Dinosauria,Theropoda), an enigmatic mid-sized megaraptoran from Patagonia

Aoniraptor libertatem is a mid-sized megaraptoran that comes from the Late Cretaceous (Turonian) Huincul Formation at Río Negro province, Patagonia, Argentina. In this study, we conducted a detailed analysis of pneumaticity of the sacrum and tail of Aoniraptor. This shows a complex structure within these vertebrae, being composed by small diverticulae surrounding large pneumatic canals and a central chamber that opens outside through pleurocoels or pneumatic canals. Further, we carried out a histologic analysis which confirms the pneumatic nature of these anatomical features. Both analyses found that chevrons in Aoniraptor were invaded by pneumaticity, a feature that appears to be unique to this taxon. In addition, a comparative analysis between Aoniraptor and other theropods (e.g. Gualicho and other megaraptorans) was carried out. This resulted in the modification of previous schemes about the evolution of pneumaticity through Theropoda, the finding of some evolutionary pneumatic traits through Megaraptora, and the usefulness of pneumatic traits as a taxonomic tool.     

Skull Anatomy and Pneumaticity of the Enigmatic Coelurosaurian Theropod Bicentenaria argentina.

The enigmatic basal coelurosaur Bicentenaria argentina is a small theropod that comes from the Upper Cretaceous of Patagonia. It is constituted by more than 130 elements, including cranial remains. These are represented by an incomplete snout, palate, dermatocranium, and lower jaws still in articulation. The skull material of Bicentenaria was preliminarily studied by previous authors. In this study, we conducted a CT scan of the holotype of Bicentenaria, which allowed us to fully describe all preserved skull bones, including some previously unknown elements. The morphological analysis indicates that Bicentenaria shares many cranial features with other basal coelurosaurs as compsognathids, Ornitholestes, and tyrannosauroids. Otherwise, results of this analysis show that Bicentenaria exhibits a set of traits unique to this taxon. Furthermore, several pneumatic recesses were closely matched with those pneumatic features present in many derived coelurosaurs, particularly tyrannosauroids. This new information, together with future discoveries, will improve our knowledge about the muscular correlates of Bicentenaria and other coelurosaurs, and may shed light about the phylogenetic relationships of this group. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1884–1900, 2020. © 2019 American Association for Anatomy     

Upper molar morphology,homologies and evolutionary patterns of chinchilloid rodents (Mammalia,Caviomorpha)

Chinchilloidea are a clade of caviomorph rodents that includes seven living species, the Dinomyidae Dinomys branickii, the Chinchillidae Lagostomus maximus, two species of Chinchilla and three species of Lagidium. In addition, two extinct families are traditionally considered chinchilloids – Neoepiblemidae and Cephalomyidae. The phylogeny of the Chinchilloidea has so far not been well established and is based on partial analyses. Studying the anatomy and ontogeny of extinct and extant taxa, we propose homologies for the upper molars of Chinchilloidea for which these homologies have not been previously proposed: that is the Chinchillidae Prolagostomus, Lagostomus, Lagidium and Chinchilla, and the Neoepiblemidae Neoepiblema and Phoberomys. We identify patterns of occlusal simplification within Chinchilloidea and evaluate its importance in an evolutionary context. A phylogenetic analysis recovered Dinomyidae, Chinchillidae and Neoepiblemidae as clades. ‘Cephalomyidae’ have not been not recovered as a monophyletic group and ‘cephalomyids’ are closely related to Neoepiblemidae. Branisamys is not included within the Dinomyidae and appears to be a basal chinchilloid.     

Skull osteology of the Eocene amphisbaenian Spathorhynchus fossorium (Reptilia,Squamata) suggests convergent evolution and reversals of fossorial adaptations in worm lizards

The fossorial amphisbaenians, or worm lizards, are characterized by a suite of specialized characters in the skull and postcranium, however fossil evidence suggests that at least some of these shared derived traits evolved convergently. Unfortunately the lack of detailed knowledge of many fossil taxa has rendered a more precise interpretation difficult. Here we describe the cranial anatomy of the oldest‐known well‐preserved amphisbaenian, Spathorhynchus fossorium, from the Eocene Green River Formation, Wyoming, USA, using high‐resolution X‐ray computed tomography (HRXCT). This taxon possesses one of the most strongly reinforced crania known among amphisbaenians, with many dermal bones overlapping each other internally. In contrast to modern taxa, S. fossorium has a paired orbitosphenoid, lacks a true compound bone in the mandible, and possesses a fully enclosed orbital rim. The last feature represents a highly derived structure in that the jugal establishes contact with the frontal internally, reinforcing the posterior orbital margin. S. fossorium also possesses a strongly modified Vidian canal with a previously unknown connection to the ventral surface of the parabasisphenoid. Comparison with the closely related fossil taxon Dyticonastis rensbergeri reveals that these derived traits are also shared by the latter species and potentially represent synapopmorphies of an extinct Paleogene clade of amphisbaenians. The presence of a reinforced orbital rim suggests selection against the loss of a functional eye and indicates an ecology potentially different from modern taxa. Given the currently accepted phylogenetic position of Spathorhynchus and Dyticonastis, we predict that supposedly ‘unique’ cranial traits traditionally linked to fossoriality such as a fused orbitosphenoid and the reduction of the eye show a more complex character history than previously assumed, including both parallel evolution and reversals to superficially primitive conditions.     

Skull Anatomy and Ontogeny of Legless Lizard Pseudopus apodus (Pallas, 1775): Heterochronic Influences on Form

Pseudopus apodus (Pallas, 1775) is the largest extant legless species of the subfamily Anguinae (Anguimorpha, Anguidae) living mostly in the sub‐arid territories ranging from the Balkan area in Europe to Kazakhstan in Asia. The species of other two genera live in North America, South‐East Asia and North Africa (Ophisaurus) and Europe and South‐West Asia (Anguis). The interrelationships of Anguinae are unresolved; this is in part the consequence of the insufficient knowledge of the cranial, postcranial and integumentary anatomy of the individual anguine species. The aim of this article is to fulfill this gap in our knowledge of the anguine anatomy. Now, in the first part of the project, the individual bones of the exocranium and visceral endocranium of the anguine legless lizard P. apodus are described in detail. In the present study, P. apodus is revealed to have autoapomorphic features of the skull which clearly distinguish it from Anguis and Ophisaurus. In addition, the study of posthatchling ontogeny of exocranium of P. apodus revealed some features, such as a nasal process of premaxilla being slightly widened in about its mid‐length, that are also typical for adults of the Ophisaurus and Anguis species as well as extinct species of Pseudopus. This strongly indicates that peramorphic heterochronic process played role in the evolution of the P. apodus skull. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:460–502, 2017. © 2016 Wiley Periodicals, Inc.     

Frontoparietal Bone in Extinct Palaeobatrachidae (Anura): Its Variation and Taxonomic Value

Palaeobatrachidae are extinct frogs from Europe closely related to the Gondwanan Pipidae, which includes Xenopus. Their frontoparietal is a distinctive skeletal element which has served as a basis for establishing the genus Albionbatrachus. Because little was known about developmental and individual variation of the frontoparietal, and its usefulness in delimiting genera and species has sometimes been doubted, we investigate its structure in Palaeobatrachus and Albionbatrachus by means of X‐ray high resolution computer tomography (micro‐CT). To infer the scope of variation present in the fossil specimens, we also examined developmental and interspecific variation in extant Xenopus. In adults of extinct taxa, the internal structure of the frontoparietal bone consists of a superficial and a basal layer of compact bone, with a middle layer of cancellous bone between them, much as in early amphibians. In Albionbatrachus, the layer of cancellous bone, consisting of small and large cavities, was connected with the dorsal, sculptured surface of the bone by a system of narrow canals; in Palaeobatrachus, the layer of cancellous bone and the canals connecting this layer with the dorsal surface of the frontoparietal were reduced. The situation in Palaeobatrachus robustus from the lower Miocene of France is intermediate—while external features support assignment to Palaeobatrachus, the inner structure is similar to that in Albionbatrachus. It may be hypothesized that sculptured frontoparietals with a well‐developed layer of cancellous (i.e., vascularized) bone may indicate adaptation to a more terrestrial way of life, whereas a reduced cancellous layer might indicate a permanent water dweller. Anat Rec, 298:1848–1863, 2015. © 2015 Wiley Periodicals, Inc.     

Morphology,paleoanthropology, and neanderthals

Morphology carries the primary signal of events in the evolutionary history of any group of organisms but has been relatively neglected by paleoanthropologists, those who study the history of the human species. Partly this is the result of historical influences, but it is also due to a rather fundamentalist adherence among paleoanthropologists to the tenets of the Neodarwinian Evolutionary Synthesis. The result has been a general paleoanthropological desire to project the species Homo sapiens back into the past as far and in as linear a manner as possible. However, it is clear that the human fossil record, like that of most other taxa, reveals a consistent pattern of systematic diversity—a diversity totally unreflected in the conventional minimalist interpretation of that record. Thus, the Neanderthals, both morphologically and behaviorally as distinctive a group of hominids as ever existed, are conventionally classified simply as a subspecies of our own species Homo sapiens—a classification that robs these extinct relatives of their evolutionary individuality. Only when we recognize the Neanderthals as a historically distinctive evolutionary entity, demanding understanding in its own terms, will we be able to do them proper justice. And we will only be able to do this by restoring morphology to its proper place of primacy in human evolutionary studies. Anat. Rec. (New Anat.) 253:113–117, 1998. © 1998 Wiley-Liss, Inc.     

The virtual brain endocast of Trogosus (Mammalia,Tillodontia) and its relevance in understanding the extinction of archaic placental mammals

After successfully diversifying during the Paleocene, the descendants of the first wave of mammals that survived the end-Cretaceous mass extinction waned throughout the Eocene. Competition with modern crown clades and intense climate fluctuations may have been part of the factors leading to the extinction of these archaic groups. Why these taxa went extinct has rarely been studied from the perspective of the nervous system. Here, we describe the first virtual endocasts for the archaic order Tillodontia. Three species from the middle Eocene of North America were analyzed: Trogosus hillsii, Trogosus grangeri, and Trogosus castoridens. We made morphological comparisons with the plaster endocast of another tillodont, Tillodon fodiens, as well as groups potentially related to Tillodontia: Pantodonta, Arctocyonidae, and Cimolesta. Trogosus shows very little inter-specific variation with the only potential difference being related to the fusion of the optic canal and sphenorbital fissure. Many ancestral features are displayed by Trogosus, including an exposed midbrain, small neocortex, orbitotemporal canal ventral to rhinal fissure, and a broad circular fissure. Potential characteristics that could unite Tillodontia with Pantodonta, and Arctocyonidae are the posterior position of cranial nerve V₃ exit in relation to the cerebrum and the low degree of development of the subarcuate fossa. The presence of large olfactory bulbs and a relatively small neocortex are consistent with a terrestrial lifestyle. A relatively small neocortex may have put Trogosus at risk when competing with artiodactyls for potentially similar resources and avoiding predation from archaic carnivorans, both of which are known to have had larger relative brain and neocortex sizes in the Eocene. These factors may have possibly exacerbated the extinction of Tillodontia, which showed highly specialized morphologies despite the increase in climate fluctuations throughout the Eocene, before disappearing during the middle Eocene.     

Vertebral pneumaticity of the North American therizinosaur Nothronychus

Nothronychus was a large, derived therizinosaur from the Upper Cretaceous of Utah and New Mexico. The genus is known from elements that have been referred to single individuals. Therizinosaurs were unusual maniraptoran theropods close to the origin of birds. The axial skeleton is extensively pneumatized, but CT scans reveal an apneumatic synsacrum. Inferred air sacs invade the basicranium, the presacral vertebrae, and the proximal caudal vertebrae, but bypassed the sacrum resulting in a caudosacral hiatus similar to some sauropods and reflecting the development of multiple diverticula from the abdominal air sac. The vertebral pneumatic chambers are described here and compared with those observed in the theropod Allosaurus and the recent avian Dinornis. The vertebrae of Nothronychus are intermediate between those two theropods. It is inferred to have possessed avian-like abdominal air sacs. This theropod would have had unidirectional lungs, as in birds, but this character cannot be related to endothermy.     

To move or not to move? Skull and lower jaw morphology of the blindsnake Afrotyphlops punctatus (Leach, 1819) (Serpentes,Typhlopoidea, Typhlopidae) with comments on its previously advocated cranial kinesis

“Scolecophidians” are traditionally known for their several skull and lower jaw autapomorphies, being conspicuously different from alethinophidian snakes in terms of skull shape and function. Although typically known for the absence of any kinetic joint in the skull dermatocranium and neurocranium—mostly due to an adaptation to fossorial habit, literature data have previously suggested a possible cranial kinesis for individuals of Afrotyphlops punctatus based on observations of live and preserved individuals. Given such observations, herein we aim to describe in detail the skull of A. punctatus based on CT-scan images of five specimens, evaluating the skull morphology and inferred function, and also providing valuable discussion on the skull osteology of the genus. Our results suggest that the skull of A. punctatus is similar to other blindsnakes in lacking any trace of snout, or even a frontal–parietal articulation. We also discuss possible osteological data that might be systematically relevant for Typhlopidae both interspecifically and intergenerically.     

Geometric morphometrics and anatomical network analyses reveal ecospace partitioning among geoemydid turtles from the Uinta Formation,Utah

We present new fossil records of the geoemydid turtle Bridgeremys pusilla from the Uinta Formation of Utah. Turtles are abundant throughout the unit, and known taxa are similar to those from the older strata in the Upper Green River Basin in Wyoming from the Bridger and Washakie Formations. B. pusilla is known from Bridgerian deposits but was not previously known from after the Turtle Bluff Member of the Bridger Formation. The taxon was coveal with two species of the geoemydid Echmatemys (E. callopyge and E. wyomingensis), a common genus of extinct pond turtles known primarily from lacustrine and fluvial deposits in western North America, including the Uinta Basin. In addition to previously documented morphological differences, our geometric morphometric analyses revealed significant differences in epiplastral morphology between B. pusilla and the two coeval Echmatemys species. Bridgeremys pusilla shared several morphological characters with Testudinidae. However, our anatomical network analysis suggests that the carapace of B. pusilla distributed stress forces in a manner more similar to emydids (basal and derived) than to derived testudinoids (Testudinidae and Emydidae), including Echmatemys species. This finding changes our understanding of the ecology of the species and sheds light onto how geoemydid turtles of the Uinta Formation may have partitioned the available ecospace. These new Uintan records extend the geographic range of B. pusilla into the Uinta Basin and stratigraphically through the top of the Uinta Formation, extending the temporal range of the taxon by more than 4 million years through the Uintan North American Land Mammal Age to the base of the Duchesne River Formation.