Thierry Smith

‘Thoracosaurs’ are Late Cretaceous to early Palaeogene longirostrine eusuchian crocodyliforms from coastal marine deposits in Europe and North America. Their phylogenetic placement is debated; whereas most morphological studies place them within Gavialidae, implying extensive ghost lineages inconsistent with molecular‐based divergence estimates, analyses applying tip‐dated Bayesian inference in a total evidence framework retrieve thoracosaurs outside of Crocodylia. Recent advances in computed tomography (CT) scanning of eusuchian skulls have allowed exploration of endocranial anatomy, an additional morphological resource that could contribute to resolving conflicting phylogenetic hypotheses, and shed light on their ecology. Here, we use CT scanning to reconstruct the endocranial cavities of three thoracosaur skulls: Thoracosaurus isorhynchus from the Maastrichtian of France and Danian of Sweden, and Eothoracosaurus mississippiensis from the Maastrichtian of the USA. Dorsal expansions of the olfactory region within the lacrimals and prefrontals, enlarged semicircular canals of the inner ear, and the absence of a bony wall between the vestibule and the encephalic endocast support a marine ecology for thoracosaurs, consistent with their depositional record and biogeographic distribution. Expansive nasopharyngeal ducts indicate that thoracosaurs were probably incapable of deep diving; instead, they may have used them for acoustic signalling. Comparison of endocranial features of thoracosaurs to extinct and extant crocodyliforms suggests that many of these characteristics are affected by longirostry and/or ecological adaptation. Our results do not clearly support either phylogenetic hypothesis for the position of ‘thoracosaurs’. Rather, our study highlights the need for increased taxon sampling to clarify the phylogenetic distribution of endocranial features across Crocodyliformes.

Carnivoran mammals (cats, dogs, bears, seals, etc.) and their kin radiated during the Palaeogene, among other carnivorous clades (hyaenodonts, mesonychians, and oxyaenodonts). This radiation has often been framed as a competition ultimately won by carnivorans, but the data supporting this hypothesis largely originate from North America. We derive body mass (BM) from dental measurements in European hyaenodonts, mesonychians, oxyaenodonts, and carnivoramorphans ranging from the latest Palaeocene to the end of the Oligocene (MP 6–30; 57.2–23.3 Ma) and compare those with North American data. We show that European assemblages tell a different story, with a marked increase of the disparity of carnivoramorphan BMs at and after the Middle Eocene Climatic Optimum (MECO; 40 Ma), with no clear effect on hyaenodonts. The ‘Grande Coupure’ (Eocene–Oligocene transition, approx. 34–33.5 Ma) marks the onset of a progressive decrease in the mean BM of hyaenodonts, while carnivoramorphans continue their rise initiated around the MECO. The observed BM patterns therefore do not follow the expected double-wedge pattern of competitive replacement and are possibly best explained by climate change-induced biodiversity dynamics.

Perissodactyls were a diverse order of mammals in the Northern Hemisphere during the Paleogene, but very few species remain today. They first appear during the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma) on the three continents of the Northern Hemisphere. Because they lack modern diversity, the study of their evolutionary history remains difficult, relying almost exclusively on fossils. In addition, their origin and early diversification remain elusive since all main groups appear at the same time with several genera and are already diverse, contrary to other modern mammal orders. Here, we investigate the early evolution of perissodactyls by analyzing a new dataset focusing on early species to obtain a new expansive phylogeny. This new topology, in combination with new observations and comparisons demonstrates that several genera are synonymous, simplifying the evolutionary picture of early perissodactyls. We show that the number of genera was overestimated and should be significantly reevaluated. These results also highlight fast dispersals of two genera, Pliolophus and Cardiolophus , on the three Northern continents, reflecting that of other modern mammals. The phylogeny also supports a potential Indo-Pakistani origin of perissodactyls. In addition, this large-scale phylogeny shows that many species that were named as “ Hyracotherium ” in the past (or sometimes “ Eohippus ”, the “dawn-horse”) and considered as “horses”, are not actually closely related to horses (Hippomorpha), including Hyracotherium itself, but can be considered as basal perissodactyls.

Marine sedimentary rocks of the late Eocene Pagat Member of the Tanjung Formation in the Asem Asem Basin near Satui, Kalimantan, provide an important geological archive for understanding the paleontological evolution of southern Kalimantan (Indonesian Borneo) in the interval leading up the development of the Central Indo-Pacific marine biodiversity hotspot. In this paper, we describe a moderately diverse assemblage of marine invertebrates within a sedimentological and stratigraphical context. In the studied section, the Pagat Member of the Tanjung Formation records an interval of overall marine transgression and chronicles a transition from the marginal marine and continental siliciclastic succession in the underlying Tambak Member to the carbonate platform succession in the overlying Berai Formation.The lower part of the Pagat Member contains heterolithic interbedded siliciclastic sandstone and glauconitic shale, with thin bioclastic floatstone and bioclastic rudstone beds. This segues into a calcareous shale succession with common foraminiferal packstone/rudstone lenses interpreted as low-relief biostromes. A diverse trace fossil assemblage occurs primarily in a muddy/glauconitic sandstone, sandy mudstone, and bioclastic packstone/rudstone succession, constraining the depositional setting to a mid-ramp/mid to distal continental shelf setting below fair-weather wave base but above storm wave base.Each biostrome rests upon a storm-generated ravinement surface characterized by a low-diversity Glossifungites or Trypanites trace fossil assemblage. The erosional surfaces were colonized by organisms that preferred stable substrates, including larger benthic foraminifera, solitary corals, oysters, and serpulid annelid worms.The biostromes comprised islands of high marine biodiversity on the mud-dominated Pagat coastline. Together, the biostromes analyzed in this study contained 13 genera of symbiont-bearing larger benthic foraminifera, ~40 mollusk taxa, at least 5 brachyuran decapod genera, and 6 coral genera (Anthemiphyllia, Balanophyllia, Caryophyllia, Cycloseris, Trachyphyllia, and Trochocyathus), as well as a variety of bryozoans, serpulids, echinoids, and asterozoans. High foraminiferal and molluscan diversity, coupled with modest coral diversity, supports the hypothesis that the origin of the diverse tropical invertebrate faunas that characterize the modern Indo-Australian region may have occurred in the latest Eocene/earliest Oligocene.

The present 3D dataset contains 3D models of new material from the middle Eocene of the Upper Subathu Formation in the Kalakot area (India), documenting the anterior dentition of the raoellid Indohyus indirae. Raoellidae are closely related to stem cetaceans and bring crucial information to understand the earliest phase of land to water transition in Cetacea.

The Messel Pit is a Konservat-Lagerstätte in Germany, representing the deposits of a latest early to earliest middle Eocene maar lake, and one of the first palaeontological sites to be included on the list of UNESCO World Heritage Sites. One aspect of Messel that makes it so extraordinary is that its sediments are rich in different fossilised organisms – microfossils, plants, fungi, invertebrate animals and vertebrates – that are rarely preserved together. We present an updated list of all taxa, named or not, that have been documented at Messel, comprising 1409 taxa, which represent a smaller but inexactly known number of biological species. The taxonomic list of Labandeira and Dunne (2014) contains serious deficiencies and should not be used uncritically. Furthermore, we compiled specimen lists of all Messel amphibians, reptiles and mammals known to us. In all, our analyses incorporate data from 32 public collections and some 20 private collections. We apply modern biodiversity-theoretic techniques to ascertain how species richness tracks sampling, to estimate what is the minimum asymptotic species richness, and to project how long it will take to sample a given proportion of that minimum richness. Plant and insect diversity is currently less well investigated than vertebrate diversity. Completeness of sampling in aquatic and semiaquatic, followed by volant, vertebrates is higher than in terrestrial vertebrates. Current excavation rates are one-half to two-thirds lower than in the recent past, leading to much higher estimates of the future excavation effort required to sample species richness more completely, should these rates be maintained. Species richness at Messel, which represents a lake within a paratropical forest near the end of the Early Eocene Climate Optimum, was generally higher than in comparable parts of Central Europe today but lower than in present-day Neotropical biotopes. There is no evidence that the Eocene Messel ecosystem was a “tropical rainforest.”

Eosuchus lerichei is a gavialoid crocodylian from late Paleocene marine deposits of northwestern Europe, known from a skull and lower jaws, as well as postcrania. Its sister taxon relationship with the approximately contemporaneous species Eosuchus minor from the east coast of the USA has been explained through transoceanic dispersal, indicating a capability for salt excretion that is absent in extant gavialoids. However, there is currently no anatomical evidence to support marine adaptation in extinct gavialoids. Furthermore, the placement of Eosuchus within Gavialoidea is labile, with some analyses supporting affinities with the Late Cretaceous to early Paleogene “thoracosaurs.” Here we present novel data on the internal and external anatomy of the skull of E. lerichei that enables a revised diagnosis, with 6 autapormorphies identified for the genus and 10 features that enable differentiation of the species from Eosuchus minor. Our phylogenetic analyses recover Eosuchus as an early diverging gavialid gavialoid that is not part of the “thoracosaur” group. In addition to thickened semi‐circular canal walls of the endosseous labyrinth and paratympanic sinus reduction, we identify potential osteological correlates for salt glands in the internal surface of the prefrontal and lacrimal bones of E. lerichei. These salt glands potentially provide anatomical evidence for the capability of transoceanic dispersal within Eosuchus, and we also identify them in the Late Cretaceous “thoracosaur” Portugalosuchus. Given that the earliest diverging and stratigraphically oldest gavialoids either have evidence for a nasal salt gland and/or have been recovered from marine deposits, this suggests the capacity for salt excretion might be ancestral for Gavialoidea. Mapping osteological and geological evidence for marine adaptation onto a phylogeny indicates that there was probably more than one independent loss/reduction in the capacity for salt excretion in gavialoids.