Search

After about a century, the skull of the holotype and sole specimen of Arambourgia gaudryi from the Eocene of Quercy (France) is here redescribed. Its interest resides in its extreme morphology, such as its very small skull and altirostral condition, that raises questions about its maturity, taxonomic validity, and paleoecology. In order to reveal previously hidden anatomical details, we used computed microtomography (µCT-scan) data to digitally extract the bones of the cranium and mandible, as well as the endocranial structures. Here, we update the osteological description of A. gaudryi, outlining new characters and re-evaluating anatomical details. Comparing it with ontogenetic series of extant crocodylians, we confirm that the specimen is a mature individual of a dwarf species with pedomorphic features. Our phylogenetic analyses indicate that A. gaudryi is an alligatorine. Comparisons with other small alligatoroid taxa show that it is indeed a valid species. The depositional environment of the finding site suggests a continental context with a karstic network. Taking this into account, together with its peculiar anatomy, we propose that A. gaudryi was a semi-terrestrial animal occupying an ecological niche similar to that of extant juvenile or dwarf crocodylians. Finally, we discuss the current knowledge of the paleobiogeography of Alligatoroidea in Europe during the Paleogene. Arambourgia gaudryi was likely part of a group of small early globidontans that arrived in the Old World, probably from North America, around the end of the Paleocene and that dispersed to at least four localities of the ancient European archipelago. [ABSTRACT FROM AUTHOR]

The Paleocene deposits from the Cerrejón Formation (Colombia, South America) have provided abundant snake remains. All this material has been assigned to the giant snake Titanoboa cerrejonensis. Here, we describe six vertebrae from among the referred materials that do not correspond to Titanoboa. All six vertebrae are morphologically identical, of a similar size, and display a distinct morphology that differs from Titanoboa. This new and unnamed taxon is a large snake estimated to be around eight meters in total length. Anatomical comparisons show that these vertebrae possess certain features typical of the Palaeophiidae, a group of extinct snakes of uncertain relationships known almost exclusively from vertebrae. Among the Palaeophiidae, the new taxon resembles the more generalized forms assigned to the genus Palaeophis, but lacks the extreme aquatic adaptations that define forms assigned to the genus Pterosphenus. We regard the new taxon as an undetermined palaeophiine but do not assign it to Palaeophis as a number of features differ from that described genus. This new record expands the known diversity of aquatic snakes from the Paleogene of South America and provides a substantial new record for the paleogeographic distribution of the Palaeophiidae. The oldest records are from the Cretaceous of Africa, while Paleocene records are poorly known and restricted to Africa, North America, and Europe. The majority of vertebral forms assigned to Palaeophiidae are from the Eocene, principally from the Tethys region, with only one previous South American record coming from the Eocene of Ecuador. [ABSTRACT FROM AUTHOR]

The earliest phases of mammalian recovery following the Cretaceous–Paleogene (K–Pg) mass extinction are incompletely known but crucial to understanding the development of modern terrestrial ecosystems. Here we report new mammalian faunal data from three vertebrate microfossil assemblages in the Hell Creek region of northeastern Montana, the deposition of which we constrain to within the first 28–80 ka of the Paleocene using new stratigraphic observations within a high-resolution chronostratigraphic framework. We quantified the taxonomic diversity among these three assemblages and five other assemblages from both the Hell Creek region and Denver Basin, together spanning the first ca. 300 ka post-K–Pg mass extinction. Our results allowed us to sub-divide the established 'disaster' and 'recovery' phases of recovery into the following sub-phases: (i) early disaster, characterized by the presence of 'dead clades walking,' high relative abundance of bloom taxa, and the appearance of post-mass-extinction immigrants, (ii) late disaster, characterized by a reduction in the number of 'dead clades walking,' continued high relative abundance of bloom taxa, and a more diverse assemblage of immigrants, (iii) early recovery, characterized by decreased relative abundance of bloom taxa, and continued immigration, and (iv) late recovery, characterized by the onset of in situ diversification. We note important differences in the pattern and timing of mammalian faunal succession between the Hell Creek and Denver Basin, suggesting that post-K–Pg mammalian recovery was spatially heterogeneous. Our results provided a new model for post-K–Pg mammalian biotic recovery that can now be tested with other earliest Paleocene assemblages across western North America. [ABSTRACT FROM AUTHOR]

Reported here is the discovery of a new mammal from the middle Paleocene of the Ouled Abdoun phosphate basin, Morocco. Hadrogeneios phosphaticus, gen. et sp. nov., is described based on dental and gnathic specimens. Comparative dental anatomy and CT scan observations support stem relationships to paenungulates. The cladistic analysis relates Hadrogeneios to paenungulatomorphs, especially based on the shared morphotypic condition of a dilambdodont ectoloph linked to inflated stylar cusps. Within the Paenungulatomorpha, Hadrogeneios is plesiomorphic not only with respect to crown paenungulates, but also to Abdounodus and Ocepeia, making it the basalmost known paenungulatomorph. Hadrogeneios, on the other hand, displays a peculiarly specialized mandibular symphyseal region (mentum), which is enlarged and raised high above the cheek teeth, and bears at its apex small incisors that are innervated and vascularized by a peculiar long and thin dorsal canaliculus. This is tentatively interpreted as a plier-like dental apparatus specialized for enhanced oral gripping function of the food, with increasing grip strength or enhanced grip precision. A composite reconstruction of the lower jaw of Hadrogeneios phosphaticus, based on 3D modeling from CT scans, is provided. Hadrogeneios, Abdounodus, and Ocepeia, all from the same Ouled Abdoun Paleocene phosphate levels, are the very rare witnesses of the first evolution and diversification of the endemic African ungulates phylogenetically preceding the modern paenungulate orders. [ABSTRACT FROM AUTHOR]

The Madtsoiidae are an extinct lineage of snakes known from the Late Cretaceous to the Late Pleistocene, with a rich fossil record distributed mainly across Gondwanan landmasses. However, only a few taxa are represented by cranial or articulated remains, and most madtsoiids are known only by isolated vertebrae. The unambiguous record of Madtsoiidae from the Cenozoic in South America had been restricted to the genus Madtsoia from Eocene and Oligocene deposits of Patagonia and Brazil. Here, we describe a new madtsoiid taxon, Powellophis andina gen. et sp. nov., based on an articulated postcranial skeleton from the Mealla Formation (middle–late Paleocene) in northwestern Argentina. The new taxon is estimated to be around 3 meters long, with a vertebral morphology sharing similar features with other mid-to-large forms. Its inclusion in a recent analysis of madtsoiid relationships recovers Powellophis as an early member of a clade formed by mostly large bodied and gigantic taxa. Its presence in the Paleocene of northwestern Argentina fills the gap between the diverse Late Cretaceous and Eocene–Oligocene records of madtsoiids in South America, confirms their presence in northern Gondwana by the early Paleogene, and expands the diversity of the group. [ABSTRACT FROM AUTHOR]

Xenarthra are an endemic and relictual clade of Placentalia that played an important role in the biodiversity during the Cenozoic in today South America. Fossil forms representing close to 200 genera have been identified, both Pilosa and Cingulata, during its long evolutionary history (late Paleocene/early Eocene–Recent). However, there is an evident imbalance in what concerns the knowledge of the xenarthrans of southern South America compared with those of middle and low latitudes, of which little is known, despite the fact that in recent times the studies of these latter have been greatly improved. New remains of Xenarthra (Folivora Mylodontinae gen. et sp. indet. and Cingulata Glyptodontidae gen. et sp. indet.) from the Letrero Formation, upper Miocene (ca. 11–9 Ma, Tortonian) of southern Ecuador are here reported and described. The only previous record from this formation belongs to the Cingulata Dasypodidae Anadasypus aequatorianus. Our comparative study reveals several morphological differences compared with other known Miocene specimens, especially those of La Venta (Colombia), Anzoátegui and Urumaco (Venezuela), and the Patagonian region (Argentina). These morphological differences suggest that these remains could belong to new taxa, and highlight the fact that, despite the relative proximity, both chronological and geographic, of the middle Miocene of La Venta (Colombia, ca. 13–11 Ma, Serravallian to Tortonian), the Xenarthra registered in Ecuador are morphologically distant, suggesting some isolation of this putative endemic paleofauna. [ABSTRACT FROM AUTHOR]