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Article Reference A juvenile skull from the early Palaeocene of China extends the appearance of crocodyloids in Asia back by 15–20 million years
The earliest Crocodylia from Asia have been represented so far only by alligatoroids and planocraniids. Although definitive crocodyloids are not known until the late Eocene, it has been hypothesized that Asiatosuchus-like basal crocodyloids originated in Asia before the late Palaeocene. In this paper, we describe a new fossil crocodyloid from the lower Palaeocene of Qianshan Basin, Anhui Province, China. The skull and lower jaw fragment exhibit several characteristics typical of juvenile crocodylians. They also display a combination of features not seen in any other taxon, warranting the erection of a new species and genus, Qianshanosuchus youngi gen. & sp. nov. Its affinities are tested in phylogenetic analyses based on two recent character matrices of Eusuchia. To assess the effect of juvenile characteristics on the outcome of the phylogenetic analyses, juvenile specimens of extant crocodylian taxa are analysed in the same way, showing that the effect of their ontogenetic stage on their placement in the tree is minimal. Our analyses point to a basal crocodyloid position for Q. youngi. With these findings, the presence of Crocodyloidea in Asia is extended to the early Palaeocene, 15–20 Myr earlier than formerly thought. Furthermore, our results corroborate previous hypotheses of a Palaeocene dispersal route of Asiatosuchus-like crocodyloids from Asia into Europe.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference New evidence of the emergence of the East Asian monsoon in the early Palaeogene
Previous palaeoenvironmental reconstructions have implied that East Asia was dominated by a zonal climate pattern during the Eocene, with an almost latitudinal arid/semiarid band at ~ 30° N. However, this long-standing model has recently been challenged by growing body of multidisciplinary evidence. Some studies indicated that central China was characterized by climatic fluctuations between humid and drier conditions during the Early Eocene, akin to the present East Asian monsoon (EAM) regime. Using palynological assemblages in the Tantou Basin, central China, we quantitatively reconstructed climate changes from the Late Palaeocene to Early Eocene to better understand climate change in central China. Palynological assemblages revealed that the coniferous and broad-leaved mixed forest in this area received no less than 800 mm of annual precipitation and experienced a climate change from warm and wet to relatively cool and dry. According to palaeoclimate curves, a sudden climate change occurred in the Early Eocene, with the mean annual temperature and precipitation decreasing by 5.1 °C and 214.8 mm, respectively, and the climate became very similar to the present climate, which is controlled by the monsoon. Therefore, this significant climate change during the Early Eocene may signal the emergence of the EAM in East Asia.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference Revision of the oldest varanid, Saniwa orsmaelensis Dollo, 1923, from the earliest Eocene of northwest Europe
Saniwa is an extinct genus of varanid squamate from the Eocene of North America and Europe. Up to now, only one poorly known species, Saniwa orsmaelensis Dollo, 1923, has been reported from Europe. Diagnostic material was limited to vertebrae with only preliminary description and no figure provided, except of one dorsal vertebra that was designated as the lectotype. New specimens from the earliest Eocene of Dormaal, Belgium and Le Quesnoy, France, including recently recovered skull ma-terial, are described and illustrated here. These fossils representing the oldest varanid squamate allow further comparisons with the type species, Saniwa ensidens Leidy, 1870, from the early and middle Eocene of North America and to propose a new diagnosis for S. orsmaelensis. Its arrival in Europe is probably linked to rapid environmental changes around the Paleocene Eocene Thermal Maximum (PETM). The occurrence of S. orsmaelensis is restricted to the early Eocene of northwest Europe and paleogeographic considerations regarding the distribution of the genus Saniwa Leidy, 1870 suggest an Asian origin, but an African origin cannot be completely excluded.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference A new gecko from the earliest Eocene of Dormaal, Belgium: a thermophilic element of the ‘greenhouse world’
We here describe a new gekkotan lizard 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 (Myr). This new taxon, with an age of 56 Myr, together with indeterminate gekkotan material reported from Silveirinha (Portugal, MP 7) represent the oldest Cenozoic gekkotans known from Europe. Today gekkotan lizards are distributed worldwide in mainly warm temperate to tropical areas and the new gecko from Dormaal represents a thermophilic faunal element. Given the Palaeocene–Eocene thermal maximum at that time, the distribution of this group in such northern latitudes (above 50° North – the latitude of southern England) is not surprising. Although this new gekkotan is represented only by a frontal (further, dentaries and a mandibular fragment are described here as Gekkota indet. 1 and 2—at least two gekkotan species occurred in Dormaal), it provides a new record for squamate diversity from the earliest Eocene ‘greenhouse world’. Together with the Baltic amber gekkotan Yantarogekko balticus, they document the northern distribution of gekkotans in Europe during the Eocene. The increase in temperature during the early Eocene led to a rise in sea level, and many areas of Eurasia were submerged. Thus, the importance of this period is magnified by understanding future global climate change.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference New data on Barbatodon oardaensis Codrea, Solomon, Venczel & Smith, 2014, the smallest Late Cretaceous multituberculate mammal from Europe
Surprisingly, after the Early Cretaceous taxonomic diversity recorded in Europe, which probably is largely an artifact of inadequate taxonomy and inflation of taxa, multituberculate mammals became extremely scarce in the Late Cretaceous in this continent, being reported exclusively from the uppermost Cretaceous continental deposits of the so-called “Haţeg Island” in Transylvania, Romania. Such mammals have been documented from the Haţeg and Rusca Montană sedimentary basins, as well as from the southwestern area of the Transylvanian Basin. All these records belong to the endemic family Kogaionidae. The present paper reports additional data related to the smallest Cretaceous kogaionid, Barbatodon oardaensis Codrea, Solomon, Venczel & Smith, 2014 based on a series of new isolated teeth recovered mainly from the type locality, Oarda de Jos (Oarda A). Furthermore, the fossil locali-ties Oarda B and Vălioara are other new occurrences for the species. Based on this new material, the intraspecific variability of B. oardaensis is confirmed and its presence is attested in the three basins. Details related to the diversity of the “Haţeg Island” kogaionids are also provided.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference Brawn before brains in placental mammals after the end-Cretaceous extinction
Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate. Later in the Eocene, multiple crown lineages independently acquired highly encephalized brains through marked growth in sensory regions. We argue that the placental radiation initially emphasized increases in body size as extinction survivors filled vacant niches. Brains eventually became larger as ecosystems saturated and competition intensified.
Located in Library / RBINS Staff Publications 2022 OA
Article Reference Evolution of European carnivorous mammal assemblages through the Palaeogene
The rise of Carnivora (Mammalia: Laurasiatheria) is an important evolutionary event that changed the structure of terrestrial ecosystems, starting at the dawn of the Eocene, 56 Mya. This radiation has been mainly analysed in North America, leaving the evolution of carnivoran diversity in other regions of the globe poorly known. To tackle this issue, we review the evolution of terrestrial carnivorous mammal diversity (Mesonychidae, Oxyaenidae, Hyaenodonta and Carnivoramorpha) in Europe. We reveal four episodes of intense faunal turnovers that helped establish the dominance of carnivoramorphans over their main competitors. We also identify two periods of general endemism. The remaining time intervals are characterized by dispersals of new taxa from North America, Asia and Africa. The European Palaeogene carnivorous mammal fauna appears to have been almost constantly in a transient state, strongly influenced by dispersals. Many of the bioevents we highlight for European carnivorous mammals are probably best seen as ecosystem-wide responses to environmental changes. In contrast to the North American record, European hyaenodonts remain more diverse than the carnivoramorphans for the entire Eocene. The replacement of hyaenodonts by carnivoramorphans as the most diverse and dominant predators only occurred after the ‘Grande Coupure’ at 33 Mya, about 16 Myr later than in North America.
Located in Library / RBINS Staff Publications 2022 OA
Inproceedings Reference Un crâne de crocodilien du Paléocène inférieur de Chine recule l'apparition des crocodyloïdes en Asie
Les plus anciens crocodiliens (Crocodylia) d’Asie ne sont représentés jusqu’à présent que par des alligatoroïdes et des planocraniidés. Bien que les crocodyloïdes ne soient pas connus avec certitude avant l’Éocène supérieur, l’hypothèse a été émise que des crocodyloïdes basaux de type Asiatosuchus étaient originaires d’Asie avant la fin du Paléocène. Nous décrivons ici un nouveau crocodyloïde fossile provenant du Paléocène inférieur du Bassin de Qianshan, province d’Anhui, Chine. Le crâne et le fragment de mâchoire inférieure associé présentent plusieurs caractéristiques typiques de crocodiliens juvéniles. Ils présentent également une combinaison de caractères non observés dans aucun autre taxon, ce qui justifie l’érection d’une nouvelle espèce et d’un nouveau genre. Les affinités phylogénétiques sont testées dans des analyses basées sur deux matrices de caractères récentes d’Eusuchia. Pour évaluer l’effet des caractéristiques juvéniles sur le résultat des analyses phylogénétiques, des spécimens juvéniles des crocodiliens actuels Alligator mississippiensis et Crocodylus niloticus ont été analysés de la même manière, montrant que l’effet de leur stade ontogénétique sur leur position dans l’arbre est minime. Nos analyses indiquent que le nouveau taxon de Qianshan occupe une position basale au sein des Crocodyloidea. La présence de ces derniers en Asie est donc reculée au Paléocène inférieur, soit 15 à 20 millions d’années plus tôt que ce que l’on pensait auparavant. De plus, nos résultats corroborent les hypothèses précédentes d’une route de dispersion paléocène des crocodyloïdes de type Asiatosuchus de l’Asie vers l’Europe.
Located in Library / RBINS Staff Publications 2022 OA
Inproceedings Reference Vestibular sensitivity and locomotor behavior in early paleocene mammals
The end-Cretaceous extinction triggered the collapse of ecosystems and a drastic turnover of mammalian communities. During the Mesozoic, mammals were ecologically diverse, but less than extant species. Modern ecological richness was established by the Eocene, but questions remain about the ecology of the first wave of mammals radiating after the extinction. Postcranial fossils are often used to determine locomotor behavior; however, the semicircular canals of the inner ear also represent a reliable proxy. These canals detect the angular acceleration of the head during locomotion and transmit neuronal signals to the brain to allow stabilization of the eyes and head. Accordingly, vestibular sensitivity to rapid rotational head movements is higher in species with a larger canal radius of curvature and more orthogonal canals. We used high-resolution computed tomography scanning to obtain inner ear virtual endocasts for 30 specimens. We supplemented these with data from the literature to construct a database of 79 fossils from the Jurassic to the Eocene and 262 extant mammals. We compared data on canal morphology and another lifestyle proxy, the size of the petrosal lobules, which have a role in maintaining eyes’ movements and position. We find that Paleocene mammals exhibited a lower average and more constricted range of Agility Indices (AI), a new measure of canal radius size relative to body size, compared to Mesozoic, Eocene and extant taxa. In the early Paleocene, body mass and canal radius increased, but the former outpaced the latter leading to an AI decline. Similarly, their petrosal lobules were relatively smaller on average compared to other temporal groups, which suggests less ability for fast movements. Additionally, Paleocene mammals had similar AIs to extant scansorial and terrestrial quadrupeds. In contrast, the lack of canal orthogonality change from the Mesozoic to the Paleocene indicates no trend toward lower vestibular sensitivity regardless of changes in body size. This result may reflect functional differences between canal orthogonality and radius size. Our results support previous work on tarsal morphology and locomotor behavior ancestral state reconstruction suggesting that ground dwelling mammals were more common than arboreal taxa during the Paleocene. Ultimately, this pattern may indicate that the collapse of forested environments immediately after extinction led to the preferential survivorship of more terrestrially adapted mammals. Funding Sources Marie Sklodowska-Curie Actions: IF, European Research Council StG, National Science Foundation, Belgian Science Policy Office, DMNS No Walls Community Initiative.
Located in Library / RBINS Staff Publications 2022 OA
Inproceedings Reference Présence d'un gecko dans l'Eocène basal de Dormaal (Belgique): un élément thermophile du PETM ?
Si le registre fossile des lézards est assez bon pour l’Eocène moyen et supérieur en Europe, il n’en va pas de même pour l’Eocène inférieur. Seule la localité de Dormaal, datant de l’Eocène basal (niveau-repère MP7,Belgique) semble faire exception. Parmi les nombreux fossiles de lézards de cette localité, nous présentons ici pour la première fois quelques rares éléments appartenant à un gecko. Ce dernier vivait donc dans nos régions durant le Maximum Thermique Paléocène-Eocène (PETM), climat le plus chaud des 66 derniers millions d’années. Ce nouveau taxon, daté de 56 Ma, est le plus ancien gecko cénozoïque connu en Europe. Avec Laonogekko lefevrei de Prémontré (MP 10, Bassin de Paris), plus jeune d’environ 5 millions d’années, ces taxons forment la radiation du Paléogène inférieur de ce clade. Aujourd’hui, les geckos sont répartis dans le monde entier, principalement dans les zones tempérées chaudes à tropicales, bien que certaines espèces puissent atteindre des régions plus froides dans les hémisphères Nord et Sud. Le nouveau gecko de Dormaal représente un élément thermophile, confirmant les préférences thermiques actuelles des geckos. Par ailleurs, la distribution de ce groupe dans des latitudes aussi septentrionales (au-dessus de 50° Nord) n’est pas surprenante durant cette période particulièrement chaude. Bien que le nouveau taxon décrit ici ne soit représenté que par un frontal et des dentaires (deux des éléments les plus fréquemment préservés chez les geckos fossiles), il fournit un nouveau record de diversité des squamates à la base de l’Eocène. Avec Yantarogekko de l’ambre éocène de la Baltique (district de Kaliningrad, nord-ouest de la Russie), ces geckos documentent la distribution septentrionale des geckos en Europe pendant l’Éocène.
Located in Library / RBINS Staff Publications 2022 OA