Ruminants reveal Eocene Asiatic palaeobiogeographical provinces as the origin of diachronous mammalian Oligocene dispersals into Europe

Faunal provincialism between the North and South parts of Eastern Asia is shown to have been in place since the late Eocene. This provincialism structured the mammalian dispersals across Eurasia for millions of years and provides insights into both palaeonvironments and palaeoclimate zonation. In addition, this study reveals the oldest record of a crown ruminant (Iberomeryx from Shinao, China). Ecologically, as well as economically, ruminant artiodactyls are one of the most important large mammal groups today. The revision of the ruminants from the Shinao Formation, from the Caijiachong marls and Xiaerhete, resulted in two new taxa and shows that the different provinces were populated by distinct taxa living in different environments, dominated by the monsoon in the South and drier conditions in the North. Evaluating this result in a Eurasian context demonstrates that the dispersals from Asia to Europe was complex. These results confirm that there were at least two dispersal events, distinct in space and time: the Grande-Coupure from Northern and Central Asia along the North ca. 34 Mya and the Bachitherium dispersal event from the Southern province along a southerly route ca. 31 Mya.

New species, revision, and phylogeny of Ronzotherium Aymard, 1854 (Perissodactyla, Rhinocerotidae)

Ronzotherium is one of the earliest Rhinocerotidae in Europe, which first appeared just after the Eocene/Oligocene transition (Grande Coupure), and became extinct at the end of the Oligocene. It is a large-sized rhinocerotid, with a special position in the phylogeny of this group, as being one of the earliest-branching true Rhinocerotidae. However, its intra-generic systematics has never been tested through computational phylogenetic methods and it is basically unknown. Its taxonomical history has gone through numerous complications, and thus we aim to provide here a complete revision of this genus, through phylogenetic methods. After a re-examination of all type specimens (five supposed species) as well as of most well-preserved specimens from all over Europe and ranging through the complete Oligocene epoch, we performed a parsimony analysis to test the position of some problematic specimens. According to our results, five species can be distinguished, Ronzotherium velaunum (type species), R. filholi, R. elongatum and R. romani as well as a new species: R. heissigi sp. nov. We also drastically re-interpret its anatomy and show that the ‘short-limbed’ “Diaceratherium” massiliae, described from Southern France, can be considered as a junior synonym of R. romani. Finally, we exclude the Asian species “Ronzotherium” orientale and “Ronzotherium” brevirostre from Ronzotherium and we consider R. kochi as a junior synonym of R. filholi.

From Toad to Frog: Description and Reattribution of the Mummified Holotype of Bufo servatus, an Eocene Anuran from France, Based on Micro-CT Examination

In the XIXth century, natural mummies of amphibians were discovered in the Quercy Phosphorites. The specific collection site has never been formally reported, which hampered precisely dating these specimens. The name Bufo servatus was erected for one these mummies, based on the external morphology of the specimen.The tomography of similarly preserved specimens, originating from this same unknown site, revealed almost complete preserved skeletons, preserved soft-tissues and gut contents. We analyze here the holotype of Bufo servatus using CT-scanning in order to investigate its potentially preserved internal features. As for the previous specimen, a subcomplete articulated skeleton was identified. Surprisingly, this skeleton is almost identical to that of Thaumastosaurus gezei, an Eocene anuran from Western Europe, to which other specimens from this mummy series were previously assigned. Few differences between the specimen skeletons highlight ontogenetic and intraspecific variations, making T. gezei a junior synonym of B. servatus, creating the new combination Thaumastosaurus servatus. Given its association with previously described Quercy specimens, this redescribed anuran is probably from the same time interval as T. gezei. Previous phylogenetic analyses have assigned T. servatus to Ranoides, with natatanuran affinities. Using data from this newly described specimen, we test here further its taxonomic affinities. Our analyses confirm this position, and formally identify T. servatus as a Natatanuran member of Pyxicephalidae (currently endemic of Equatorial Africa) and more precisely, a stem-Pyxicephalinae. This result confirms the origin of Thaumastosaurus, a member of the African herpetofauna occupying Western Europe before the Grande Coupure at the Eocene/Oligocene transition.

The upper Eocene-Oligocene carnivorous mammals from the Quercy Phosphorites (France) housed in Belgian collections

The Quercy Phosphorites Formation in France is world famous for its Eocene to Miocene faunas, especially those from the upper Eocene to lower Oligocene, the richest of all. The latter particularly helped to understand the ‘Grande Coupure’, a dramatic faunal turnover event that occurred in Europe during the Eocene-Oligocene transition. Fossils from the Quercy Phosphorites were excavated from the middle 19th century until the early 20th century in a series of sites and became subsequently dispersed over several research institutions, while often losing the temporal and geographical information in the process. In this contribution, we provide an overview and reassess the taxonomy of these barely known collections housed in three Belgian institutions: the Université de Liège, KU Leuven, and the Royal Belgian Institute of Natural Sciences. We focus our efforts on the carnivorous mammals (Hyaenodonta and Carnivoramorpha) and assess the stratigraphic intervals covered by each collection. These fossils are derived from upper Eocene (Priabonian), lower Oligocene (Rupelian), and upper Oligocene (Chattian) deposits in the Quercy area. The richness of the three collections (e.g., the presence of numerous postcranial elements in the Liège collection), the presence of types and figured specimens in the Leuven collection, and some identified localities in the RBINS collection make these collections of great interest for further studies on systematics and the evolution of mammals around the ‘Grande Coupure’.

Eocene Western European endemic genus Thaumastosaurus: new insights into the question “Are the Ranidae known prior to the Oligocene?”

Background Amphibians, due to their ecophysiological peculiarities, have a physiology dependent on environmental conditions and sensitively respond to their changes. Here, the oldest record of the genus Thaumastosaurus is described, whose fossil record known exclusively from Western Europe is discussed in the scope of the climatic changes of 33.5–40.5 Ma. Results In the present paper, the fossil remains of the genus from three localities in Switzerland (11 samples overall) have been studied and referred to the species Thaumastosaurus bottii. Its stratigraphic distribution has been revised and summarised. The studied localities present the stratigraphically oldest and the most eastern occurrences of the genus Thaumastosaurus. Eocene probable ranids (Ranidae indet./Rana sp./? Rana sp.) from Europe could be referred to Thaumastosaurus. Discussion Their first occurrence of ranids most likely coincides with a warm phase of the global climate at 40 Ma, as tropical conditions were prevailing in Europe. As a result of the gradual cooling of the global climate, the tropical conditions in Europe were replaced by drier open habitats towards the latest Eocene at 34 Ma, when the latest occurrence of the European endemic genus Thaumastosaurus is known. Taking the fossil record and the climate evolution of that time into account, it can be concluded that Thaumastosaurus represents one of the groups among the vertebrates that disappeared during the large extinction event at the Eo–Oligocene transition, known as the Grande Coupure. The fossil finds of the genus from the studied localities allow to refer the previously suggested Eocene true frogs to the genus Thaumastosaurus, hereby stating the arrival of the true frog family Ranidae by the genus Pelophylax in Europe from the east at the earliest Oligocene.

Lepidosaurian diversity in the Mesozoic–Palaeogene: the potential roles of sampling biases and environmental drivers

Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the Triassic–Palaeogene (252–23 Ma), and compare observed and sampling-corrected richness curves generated using Shareholder Quorum Subsampling and classical rarefaction. Generalized least-squares regression (GLS) is used to investigate the relationships between richness, sampling and environmental proxies. We found low levels of richness from the Triassic until the Late Cretaceous (except in the Kimmeridgian–Tithonian of Europe). High richness is recovered for the Late Cretaceous of North America, which declined across the K–Pg boundary but remained relatively high throughout the Palaeogene. Richness decreased following the Eocene–Oligocene Grande Coupure in North America and Europe, but remained high in North America and very high in Europe compared to the Late Cretaceous; elsewhere data are lacking. GLS analyses indicate that sampling biases (particularly, the number of fossil collections per interval) are the best explanation for long-term face-value genus richness trends. The lepidosaur fossil record presents many problems when attempting to reconstruct past diversity, with geographical sampling biases being of particular concern, especially in the Southern Hemisphere.

Mountain uplift explains differences in Palaeogene patterns of mammalian evolution and extinction between North America and Europe

Patterns of late Palaeogene mammalian evolution appear to be very different between Eurasia and North America. Around the Eocene–Oligocene (EO) transition global temperatures in the Northern Hemisphere plummet: following this, European mammal faunas undergo a profound extinction event (the Grande Coupure), while in North America they appear to pass through this temperature event unscathed. Here, we investigate the role of surface uplift to environmental change and mammalian evolution through the Palaeogene (66–23 Ma). Palaeogene regional surface uplift in North America caused large-scale reorganization of precipitation patterns, particularly in the continental interior, in accord with our combined stable isotope and ecometric data. Changes in mammalian faunas reflect that these were dry and high-elevation palaeoenvironments. The scenario of Middle to Late Eocene (50–37 Ma) surface uplift, together with decreasing precipitation in higher-altitude regions of western North America, explains the enigma of the apparent lack of the large-scale mammal faunal change around the EO transition that characterized western Europe. We suggest that North American mammalian faunas were already pre-adapted to cooler and drier conditions preceding the EO boundary, resulting from the effects of a protracted history of surface uplift.