Evolution of plesiadapid mammals (Eutheria, Euarchonta, Plesiadapiformes) in Europe across the Paleocene/Eocene boundary: implications for phylogeny, biochronology and scenarios of dispersal

Abstract

Plesiadapid mammals (Eutheria, Euarchonta, Plesiadapiformes) are well represented in the late Paleocene to early Eocene of Europe (reference levels MP6, MP7 and MP8+9), but relationships among the described species and their links to North American plesiadapids remain disputed. To better understand the evolution of the group in Europe, to explore its potential for biochronological dating and to test hypotheses on plesiadapid phylogenies and dispersal patterns between Europe and North America, a morphometric analysis was performed for a succession of plesiadapid assemblages bracketing the Paleocene/Eocene boundary (PEB) in the Paris Basin, including recently made collections from Montchenot (MP6) and Le Quesnoy (MP7). Both dental size and shape were analysed for nearly all positions of the permanent plesiadapid dentition. Size variation at Cernay (MP6) is consistent with the presence of at least two species of Plesiadapis. A morphological succession is found in European large-sized Plesiadapis, continuing beyond the PEB but showing no clear continuity with Eocene Platychoerops. Large-sized Plesiadapis from Berru (MP6) is distinctly different from P. tricuspidens, justifying the definition of a new species, P. berruensis. Species of Plesiadapis confirm the temporal succession of the localities Cernay, Berru, Le Quesnoy and Meudon, allowing definition of a refined biochronology in the Paris Basin, with Montchenot correlated approximately to Cernay. Comparisons between plesiadapids from Europe and North America indicate a separation from at least the terminal Tiffanian, suggesting correlation of the European reference level MP6 with the North American biozones Ti-5b and Ti-6. Convergent evolution in those lineages and in Platychoerops seems to be linked mainly to trends towards folivory.