A new latest Paleocene mammal fauna from the Great Divide Basin in southern Wyoming is described and compared with fossil assemblages of similar age elsewhere in Wyoming. The Twelvemile Gulch local fauna is currently documented by 182 mammalian (127 identifiable) specimens from two localities representing 10 orders, 18 families, and 22 species of mammals, including Phenacolemur cavatus, new species. Several characteristic taxa indicate a Clarkforkian age, but some taxa that co-occur at Twelvemile Gulch show disjunct stratigraphic ranges in the well-documented stratigraphic sequence exposed in the Clarks Fork Basin of northern Wyoming. Anachronistic occurrences of Clarkforkian taxa in northern and southern Wyoming have now been documented repeatedly. These unexpected faunal associations likely reflect changing climates and associated taxon-specific range shifts across a latitudinal gradient in the Rocky Mountain Interior. The apparently asynchronous first and last appearances of certain taxa across this latitudinal gradient highlight the utility of immigrant clades over endemic taxa in biostratigraphy. A previous biozonation scheme for the Clarkforkian of the Clarks Fork Basin emphasized endemic Plesiadapis cookei and Copecion as index taxa for Clarkforkian biozones Cf-2 and Cf-3, respectively. However, the applicability of this zonation to Clarkforkian faunas from other parts of Wyoming has been problematic because Plesiadapis cookei occurs in all of them, despite substantial evidence for age disparity among these faunas. A revised biozonation for the Clarkforkian leverages first appearances of invasive Coryphodontidae and Miacidae to discriminate later Clarkforkian faunas including Twelvemile Gulch from earlier Clarkforkian faunas such as Big Multi Quarry.

This study reports the rich occurrence of a varied chondrichthyan assemblage from the Lower Triassic of Spitsbergen based on multiple well-preserved isolated teeth. Based on distinct tooth morphology and histology, two species of the genus Synechodus are described: Synechodus incrementum and a new species cf. Synechodus rotheliusi. The new species is diagnosed based on a smooth crown surface with a sharp cutting edge and lingually inclined cusps with acute apices, where the central cusp is considerably higher than the lateral cusplets. Another group of Synechodus teeth has ornamentation where the crests form longitudinal lines at the base of the mesio-distally elongated crown and is identified as S. incrementum. In addition, two new monotypic genera, Eorapax serrasis and Wimanodon marmieri, are described from the same bonebed. Eorapax serrasis has unique morphological features, such as a monocuspid crown with a serrated cutting edge. Whereas W. marmieri is distinguished based on unique apomorphic features such as a round bulgy crown that overhangs the crown-root junction—especially at the crown shoulder. Tooth histology, including enameloid microstructures, is described for the first time and shows that these taxa are distinctly different from other known comparable genera.

Dzharacursor gen. nov. is established for the reception of Archaeornithomimus(?) bissektensis Nesov, 1995 from the Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan. Dzharacursor bissektensis is represented by cranial elements and many isolated postcranial bones that show considerable ontogenetic and some individual variation. Several of the morphological characters previously hypothesized as autapomorphies for Qiupalong henanesis and Aepyornithomimus tugrikinensis are found to be variable in the hypodigm for Dzaracursor bissektensis. Dzharacursor bissektensis is one of the oldest known ornithomimids in Asia. Phylogenetic analysis places this taxon at the base of the ornithomimid radiation, but more derived than Archaeornithomimus asiaticus.

The Late Cretaceous through Paleogene fossil record for North American eusuchians is remarkable in that it indicates high levels of survivorship across the Cretaceous–Paleogene (K–Pg) boundary, as well as an increase in diversity through the early Eocene. Despite the clade's continued existence, gaps remain in its fossil record, particularly near the K–Pg boundary and in Colorado. A eusuchian from the lower Paleocene Denver Formation of Corral Bluffs is represented by specimens identified as Borealosuchus sternbergii. Here, we provide anatomical descriptions and comparisons supported by micro-CT scan data of three partial crania. We conduct a phylogenetic analysis, the results of which are influenced by the potential sub-adult ontogenetic stage of the specimens and species-level assignment is preliminary. The specimens fill both geographic and temporal gaps in the record of the Borealosuchus species complex as the first specimens from the earliest Paleocene of Colorado. These additions highlight the uncertainty in phylogenetic relationships among the Borealosuchus species complex, the importance of taking ontogenetic stage into account when assessing such relationships, and help constrain biogeographic dispersal patterns and ecological niche occupation of the clade.

Aetiocetids are a relatively diverse group of small toothed mysticetes that lived from the late Eocene through the late Oligocene in the North Pacific Ocean. They are characterized by a combination of morphological features that places them between earlier mysticetes (e.g., mammalodontids) and chaeomysticetes. Since the first aetiocetid was described in the 1960s, their significance in understanding mysticete evolution has been broadly discussed, with particular attention to aspects of their paleobiology (i.e., feeding strategies). However, morphological features that could offer additional insight into their paleobiology, like the tympanoperiotic complex, dentition, and postcranial elements, are still poorly understood due to incomplete specimens or partial descriptions. In this context, this study provides a detailed description of Fucaia goedertorum (LACM 131146), which represents one of the most completely preserved aetiocetid specimens, thus allowing for a better understanding of the cranial and postcranial morphology of this group. The craniomandibular and postcranial morphology of Fucaia goedertorum displays a unique combination of plesiomorphic and derived characters, such as proportionately large orbits, presence of upper and lower teeth, well-defined embrasure pits, a kinetic mandibular symphysis, multi-element sternum, flexible vertebral column and proportionately long flippers, among others. Our interpretations of the cranial and postcranial morphology of Fucaia goedertorum, suggest that it was a raptorial or suction-assisted raptorial feeder with high flexibility and maneuverability, more akin to what is observed in otariids. Combined with current interpretations proposed for other aetiocetids, we suggest that this group of early mysticetes displayed a broad range of feeding strategies.

Speothos pacivorus from the Pleistocene of Brazilian Intertropical Region (BIR) is distinguished from the extant bush dog S. venaticus by its larger size and key characters of the skeleton and teeth. Nonetheless, its taxonomic status is volatile, with some authors still considering both species as synonymous. Here, we aimed to summarize morphofunctional differences between S. pacivorus and S. venaticus through a comparative description of their skull and dentition, geometric morphometric analysis (GMM), and finite element analysis (FEA). Our GMM revealed S. pacivorus significantly separated from the sampled specimens of S. venaticus, and a regression analysis showed that the morphological differences of its cranium are not size-related, reinforcing its status as a separate species. Both exhibited very akin von Mises' stress average and distribution on FEA's results, suggesting similar prey-capturing strategies. Our results bolster the hypothesis that the coexistence of these hypercarnivorous canids in the BIR could be explained by a diverse megaherbivore community, allowing resource partitioning between different canid species. Following the demise of these megaherbivores in the Pleistocene–Holocene boundary, other large hypercarnivorous canids also became extinct, leaving the small S. venaticus, able to subsist on smaller prey, as the sole surviving species of this specialized lineage.

Glyphoderma kangi from the Ladinian of the Middle Triassic is the oldest record of cyamodontoid placodonts known in South China, but several aspects of the anatomy of its skull and dorsal shell remained unknown, due to the preservation of the holotype specimen in dorsal view. Two new mostly complete and well-preserved skeletons are described here to reveal new anatomical information on the skull, pectoral girdle, pelvic girdle, transverse processes, ribs, and gastralia. In addition to the unique osteoderms with radiating grooves and ridges that form the carapace, six other types of osteoderms are found covering the skull and the mandible, composing the lateral wall, and forming an incomplete inner layer of the carapace. The inferred inner layer, formed by osteoderms located beneath the surface osteoderms near the peripheral margin of the carapace, probably helped to reinforce the carapace margins together with the dorsal ribs. Features including relative limb length indicate that Glyphoderma kangi has reached the marine adaptation step of at least M4, indicating minimized terrestrial travel and loss of terrestrial feeding. Considering its morphology and ecology, Glyphoderma kangi probably pursued a bottom-dwelling lifestyle where danger mainly came from above.

The Upper Triassic lower Dharmaram Formation of India has yielded a highly diverse archosaur-dominated fauna that included a paratypothoracin aetosaur Venkatasuchus armatum, a plateosaurian sauropodomorph Jaklapallisaurus asymmetrica, a neotheropod, and a Mystriosuchinae phytosaur. In this current contribution, we describe a new paratypothoracin aetosaur taxon, Kuttysuchus minori gen. et sp. nov., from the same horizon based on several isolated paramedian osteoderms recovered from a single fossil locality. These osteoderms are characterized by a weakly raised anterior bar with a short pointed anteromedial edge, deeply incised dorsal surface ornamentation composed of strongly radial pattern of ridges and grooves with a low density of pits surrounding a pointed pyramidal dorsal eminence placed near the posterior margin and a weakly developed ventral strut or transverse thickening. These features show similarity of the specimens to that of both Paratypothorax and Stagonolepis olenkae and strongly differentiate Kuttysuchus from the other paratypothoracin Venkatasuchus known from the same stratigraphic unit. Our phylogenetic analysis recovered Kuttysuchus as an early-diverging taxon within the clade Paratypothoracini. The rich record of paratypothoracin aetosaurs, along with that of a mystriosuchine phytosaur positively suggests a mid-to-late Norian age, though the age could be extended to the Rhaetian as suggested by previous studies. The current study considerably enhances knowledge of aetosaur diversity during the Late Triassic, particularly on Gondwana, and raises the potential of recovering a rich Gondwanan record of Paratypothoracini in future.

During the Paleogene in Afro-Arabia, most terrestrial mammalian carnivores belonged to Hyaenodonta, an extinct lineage bearing a pair of carnassials between each set of molars. The Fayum Depression of Egypt preserves multiple lineages of hyaenodonts across the Eocene–Oligocene boundary. Here, we describe one of the most complete hyaenodont crania ever recovered from the lower Oligocene of the Fayum (Jebel Qatrani Formation, Quarry I, ∼30 Ma). The cranium is about the size of a hyena's and preserves the complete upper tooth row. The long, shearing metastyle and reduced and mesially shifted protocones indicate a hypercarnivorous diet, and robust zygomatic arches suggest strong chewing muscles. Based on dental comparisons, we refer the cranium to Bastetodon syrtos (previously “Pterodon” syrtos). Bastetodon syrtos has three premolars and two molars—a reduced dental formula compared with other Fayum hyainailourines such as Akhnatenavus and European hyainailourines such as Pterodon. The cranium preserves the clover-shaped lambdoidal crest and long pharyngeal tube that unites Hyainailouroidea (Apterodontinae, Teratodontinae, and Hyainailourinae). The new Fayum cranium allows us to reevaluate the genus Pterodon and explore characters that distinguish Afro-Arabian and Eurasian species placed in this genus. Our phylogenetic analysis recovers a paraphyletic Pterodon, with B. syrtos as the sister taxon of Falcatodon schlosseri. We erect Sekhmetops to describe the large Fayum hyainailourine species S. phiomensis and S. africanus. This effort clarifies the biogeographic history of the clade that includes Pterodon, revealing multiple Tethys Seaway dispersals during the Paleogene followed by endemic radiations in Eurasia and Afro-Arabia.