EVIDENCE FOR DIRECT MAMMALIAN FAUNAL INTERCHANGE BETWEEN EUROPE AND ASIA NEAR THE PALEOCENE-EOCENE BOUNDARY

Abstract

Dispersal of mammals into Europe at the beginning of the Eocene is conventionally interpreted as being solely from North America via the Greenland land bridge, as other routes were apparently unavailable because of the intervention of major seaways. The Tethys separated Europe from Africa to the south, and the West Siberian Sea and Turgai Straits separated Europe from Asia to the east. Using cladistic analysis and paleogeographic reconstructions, three cases of multiple land mammal dispersal across the Turgai Straits from Asia to Europe in the late Paleocene and early Eocene are recognized. Two of these involve the hyopsodontid condylarths Lessnessina (with its synonym Midiagnus, and including the species L. khushuensis sp. nov.) and a Hyopsodus clade (H. orientalis + H. itinerans), which most likely entered Europe early in the Eocene at ∼54.5 Ma. The third case is of the order Perissodactyla, whose analysis provides an early history of global dispersal for the group. It indicates that their entry into Europe was earlier than for the hyopsodontids, in the latest Paleocene, perhaps at ∼56.5 Ma. As the Turgai Straits are at mid latitudes, not high latitudes like the Bering and Greenland land bridges, it is unlikely that ameliorating climate was the driving force behind these three dispersals. The cause was most likely low sea levels, providing either a narrow land bridge or a greatly narrowed strait, allowing rafting.