The early tetrapod Crassigyrinus scoticus was a large aquatic predator known from the lower- to mid-Carboniferous (upper Tournasian to upper Visean/lower Serpukovian, approximately 350–330 Ma) of Scotland and Canada. Crassigyrinus is enigmatic in terms of its phylogenetic position due to its unusual morphology, which features a mixture of primitive and derived characters. Previous reconstructions, based on five incomplete and deformed specimens, have suggested a dorsoventrally tall skull with a short and broad snout, large orbits and external nares, and an extended postorbital region. In this study, we scanned four specimens using computed tomography and segmented imaging data to separate bone from matrix and individual bones from each other. Based on these data, we present a revised description of the upper and lower jaws, including sutural morphology and abundant new anatomical information. Damage was repaired and the skull retrodeformed to create a hypothetical three-dimensional reconstruction of the skull of Crassigyrinus that is dorsoventrally flatter than earlier reconstructions, yet still morphologically unique amongst early tetrapods. Overall skull shape, the size and distribution of the teeth, sutural morphology, and the specialized anatomy of the jaw joint and mandibular symphysis all suggest that Crassigyrinus was a powerful aquatic predator capable of hunting and subduing large prey.

Unlike the eggshells of other amniotes, turtle eggshells are composed of aragonite, which is a metastable mineral. Turtle eggshells in the fossil record are therefore usually transformed to calcite. Geothermal heat also negatively affects the preservation of aragonite, and therefore the preservation of aragonite under geothermal settings is not usually expected. Here we report new turtle eggs from the Lower Cretaceous (Aptian–Albian) Hasandong Formation of South Korea, describing the morphological features of the eggs and eggshells. The eggs belong to an oogenus Testudoolithus with the smallest recorded egg size. As one of the oldest fossil eggs from Korea, this material fills a paleobiogeographic gap in the fossil record of turtle eggs in East Asia, which has limited records for the eggs of non-dinosaurian reptiles. More importantly, the presence of relict aragonite was cross-validated by electron backscatter diffraction and Raman spectroscopy. The Raman spectra of the thermally altered organic matter inside the eggshells indicated that the eggs experienced a maximum temperature of almost 260°C during their taphonomic history. This implies that aragonite can be preserved even under hostile thermal conditions and earlier reports of ‘calcite-only’ turtle fossil eggs may preserve undetected relict aragonite, which is only detectable via careful investigation using advanced microscopic techniques. The combined use of mineralogical and spectroscopic approaches adopted in this study may also be useful to invertebrate paleontology and archeology to further understand the relationship between the preservation of aragonite and the maximum paleotemperature that the materials experienced.

We here report on iguanians (both new and the previous record) from the earliest Eocene (MP 7) of the Dormaal locality in Belgium, from the time of the warmest global climates of the past 66 million years. Today iguanians are distributed mainly in the New World (Pleurodonta) and Old World (Acrodonta), having complicated biogeographic histories. Both lineages co-existed in Dormaal 56 Ma. Iguanians here document the presence of thermophilic faunas during greenhouse conditions in the northern mid-latitudes (above 50° north, the latitude of southern England). The complete maxilla of the agamid Tinosaurus europeocaenus is described and figured for the first time, being distinctive and furnishing a number of diagnostic characters. The dentary coronoid process of this species is also observed for the first time. Our morphological analysis supports the previous observation that Tinosaurus is similar to Leiolepis, but also differs from it by several distinguishing features. Some jaw character states present in T. europeocaenus are shared with the Indian T. indicus, Chinese T. doumuensis, and American Tinosaurus sp., but several differences among them are observed. Besides the well-known Geiseltaliellus, we here erect and describe a new pleurodontan taxon. The new taxon is represented by a maxilla with a unique and peculiar tooth crown morphology: the central cusp is bifurcated, markedly split into two distinct and well-separated “prongs.” This morphology likely indicates a high specialization on feeding sources. This might cause a higher extinction risk relative to generalists, because terrestrial ecosystems in Europe changed substantially during the Paleogene.

Equoid perissodactyls were diverse in the Eocene of the Iberian Peninsula, and those from the central and western Iberian basins (Mondego, Oviedo, Almazán, Duero, and Miranda-Treviño) and the eastern Ebro Basin (Ulldemolins area) were endemic, with the presence of six genera and 19 species (mainly Palaeotheriidae sensu stricto) that are unknown in the rest of western Europe. In this paper, a new endemic Eocene paleotheriid genus, Idiodontherium, gen. nov., is reported. The new genus includes two species: I. martindejesusi, from the upper middle Eocene (Bartonian) of Mazaterón (Almazán Basin, Soria, Spain) and I. astibiai, from the upper Eocene (Priabonian) site of Zambrana (Miranda-Treviño Basin, Álava/Araba, Spain). Idiodontherium exhibits an unusual dental pattern, which is characterized by an extreme shortening of the jugal series due to a great reduction of the premolar series, in combination with a long post-canine diastema. It is a small to medium-sized plagiolophine with thick enamel in comparison with other plagiolophine equoids of the same size. These new taxa exhibit peculiar dental features that could be associated with greater specialization of the diet.

A partial skull of a pachycephalosaurid from the Upper Cretaceous Hell Creek Formation, Montana, is interpreted as a new taxon, Platytholus clemensi gen. et sp. nov. MOR 2915 does not fit into an ontogenetic continuum of known pachycephalosaurids from the Hell Creek Formation, Montana, and contemporaneous sediments from the Western Interior. Comparisons to known ontogimorphs of Sphaerotholus and Pachycephalosaurus preclude including this specimen into an ontogenetic series of either taxon. We hypothesize that MOR 2915 is a new species based on a relatively low, broad dome at this advanced ontogenetic age that is neither round nor oval in dorsal view, distinct but fused lateral cranial elements fully incorporated into the dome without any dorsal lobe differentiation, and individual tab-like tubercle ornamentation dorsolaterally. Phylogenetic analysis posits that Platytholus clemensi is a Prenocephale-grade taxon deeply nested within Pachycephalosaurinae, but it is not a member of Pachycephalosaurini. Platytholus clemensi is intermediate in size between the other contemporaneous pachycephalosaurids in the Hell Creek Formation and suggests a diverse set of taxa-partitioned ecological niches by body size. We confirm a well organized, major internal vascular network using high resolution computed tomography. Foramina present on the orbital roofs indicate these canals penetrated the entire ceiling of the orbits within the frontal and supraorbital bones. Abundant neurovascular canals passing through the dome to the ectocranial surface indicate a keratinous structure of some kind, possibly with a vertical structural framework, was present on the dome. We review the history of the head-butting hypothesis and associated behavioral implications.

Fossil records of canids are rare and incomplete in South America. In Chile, all well-identified taxa are part of the “South American Canid Clade” and come from sites located in southern Patagonia. Here, we report the first record for Chile of a taxon of the “Canis clade,” assigned to cf. Aenocyon dirus. The fossil remains consist of a partially complete left hind limb, exposed by aeolian deflation, which facilitated its discovery at an isolated setting in Quebrada Maní, named QM38 site, in the southern sector of the Pampa del Tamarugal basin, part of the hyperarid core of the Atacama Desert, northern Chile. Measurements of the fossil are larger than the Protocyon troglodytes, falling in the smaller size range of A. dirus and within the larger range of Theriodictis platensis. Its morphological features compared with bone references of large extinct canids show that the fossil belongs to a small-sized Aenocyon. The remains occur in surface silty clays deposited by an alluvial fan that was active in the Pampa del Tamarugal basin in the Late Pleistocene. A radiocarbon date from bone apatite yielded an age of 14,660 cal years BP, placing it within the first half of the Central Andean Pluvial Event when this basin was wetter, well vegetated, and inhabited by large, medium, and small herbivores. No other large predator records are known from this basin, and our find affords a more complete view of this ecosystem which thrived in the hyperarid core of the Atacama during the Late Pleistocene.

Ranids represent an important part of the extant anuran diversity of Europe. One of the best-known genera is Pelophylax (green-water frog). This genus is considered to have arrived in Europe during the Eocene/Oligocene transition, with numerous occurrences of the genus throughout European Oligocene sites. Unfortunately, most of the specimens are isolated bones, hampering our understanding of the diversity and evolution of the genus during this time. We here present the description of an incomplete but articulated anuran skeleton from the lowest Oligocene of Chartres-de-Bretagne (western France). This specimen, missing its head, preserves almost all postcranial bones articulated and skin impressions. The osteological description allows to assign this specimen to Pelophylax kl. esculentus, making it one of the oldest known occurrences of the genus. We also suggest that specimens assigned to the late Oligocene “Rana” aquensis should be referred to the genus Pelophylax. The presence of a Pelophylax in western Europe during the early Oligocene indicates that the genus had already spread throughout Europe, no later than 5 Ma after its emergence in the eastern part of the continent. It suggests that Pelophylax benefitted from the extinction of ranoids during the “Grande Coupure.”

Post Cretaceous–Paleogene (K–Pg) boundary continental ecosystems of Europe host a distinctive assemblage of derived neosuchians related to modern semi-aquatic lineages, including the alligatoroid Diplocynodon and the crocodyloid Asiatosuchus but also a less well-understood group known as the Planocraniidae. Yet, uniquely in its faunal composition, Europe also preserves some of the last representatives of Notosuchia, a group that previously underwent a successful radiation in terrestrial ecosystems of the Cretaceous, especially in Gondwana. Although Europe harbored a few members of Sebecosuchia during the Cretaceous, their affinities with post-K–Pg forms is not ascertained, in part due to their rare and fragmentary nature on both sides of the stratigraphic boundary. Paleogene European sebecosuchians have been reported from the Eocene of France, Germany, Portugal, and Spain. Resolving their phylogenetic position may shed light on their suspected Gondwanan affinities. Based on new cranial and postcranial remains, we provide a description of the most complete and largest European sebecosuchian to date from the middle Eocene (Bartonian) of Issel and Réalmont, southern France. Dentaneosuchus gen. nov. is proposed to designate the taxon originally described as Atacisaurus crassiproratus. A phylogenetic analysis recovers Dentaneosuchus crassiproratus as the basalmost branching member of Sebecidae, a clade otherwise known from abundant specimens from the Paleogene and Miocene of South America. Among post-K–Pg sebecids, Dentaneosuchus crassiproratus rivalled in size with Barinasuchus arveloi from the Miocene of Venezuela, demonstrating that sebecids achieved the status of apex predators in terrestrial ecosystems of both Europe and South America.

Osteostracans are stem-gnathostomes with bony tissues that represent an important link between living jawed and jawless vertebrates, the latter of which lack skeletal hard tissues. In this study, a number of skeletal microremains from a diverse group of osteostracans called thyestiids have been investigated using propagation phase-contrast X-ray synchrotron microtomography. This enabled detailed reconstructions of their three-dimensional vasculature. The dermal skeleton of thyestiids is divided into three layers that vary in proportion between taxa, similar to gnathostomes and other osteostracans. The basal layer is confirmed as an acellular bony tissue composed of fiber bundles that contains narrow, vertical canals and/or large cavities. Bundles bend around smaller canals but form jagged edges around larger cavities, which suggests delayed mineralization. The presumed vascular mesh canals of the deep middle layer are radially arranged in some taxa, but more irregular or even tree-like in others, suggesting a relation to how the elements developed and grew. A number of mesh canals ascend toward the superficial layer where they supply the subepidermal vascular plexus, or create pore fields that open to the surface in some taxa. These ascending mesh canals most likely expanded and formed a network of canals underneath more extensive pore fields. Aestiaspis viitaensis has a simple upper canal system above these fields, while Tremataspis mammillata and Tr. milleri scales have a polygonal network of upper mesh canals above extensive perforated septa. These systems are most likely homologous, but their relation to intra- and inter-areal canals described in other osteostracans remains ambiguous.

We report on the discovery of new skulls and dentitions documenting a broader geographic and stratigraphic range for the eutherian mammal Asioryctes nemegtensis. Originally discovered in the Upper Cretaceous Barun Goyot Formation of the Gobi Desert, Mongolia, A. nemegtensis has been hypothesized to be absent from the Djadokhta Formation, another Upper Cretaceous Gobi Desert formation. This distinction has previously contributed to an emphasis on faunal and age dissimilarity between the two sets of Cretaceous rocks. Here we report four new specimens of A. nemegtensis from the Djadokhta Formation and document its first co-occurrence with its sister taxon, Ukhaatherium nessovi. The new specimens reveal additional details about the cranial and dental anatomy of asioryctitheres and prompt an alpha taxonomic revision and emended diagnosis for A. nemegtensis. Among the new specimens are a nearly complete skull and several articulated jaws, which provide new information on tooth occlusion. These discoveries are an additional datapoint indicating that some Upper Cretaceous faunal assemblages in Mongolia are not as distinctly different in composition and age as has been previously hypothesized.