POST-EOCENE TERRESTRIAL MAMMAL DISPERSAL VIA THE NORTH ATLANTIC (Invited Presentation)

Biotic interchange (i.e., the movement of organisms among regions and continents) among Europe, Asia and North America over the last 66 Ma shaped global mammal biodiversity. However, for most clades, the number and timing of dispersals remain poorly understood. Herein, we aim to reconstruct the biogeographic history of rhinocerotids and ursids, both clades with considerable past diversity and geographic ranges that encompassed much of the globe. Using a fossilized birth-death approach, we estimated the largest, time-calibrated phylogeny of Cenozoic rhinocerotids, to date. For ursids, we created a time-calibrated supertree based on published phylogenetic hypotheses. We then used the maximum likelihood approach in BioGeoBEARS to fit an array of biogeographic models (e.g., Dispersal‐Extinction Cladogenesis (DEC), DEC+jump dispersal) and stochastic character mapping to infer the number of biotic interchange events among Asia, Europe, North America, South America (for ursids), and Africa. For both clades, we found that the highest rates of biotic interchange, unsurprisingly, occurred between Europe and Asia. However, the next highest number of exchanges occurred between Europe and North America. Furthermore, we show that dispersal between Europe and North America occurred during the Oligo-Miocene, suggesting the North Atlantic route may have been passable for mammals millions of years longer than previously proposed; typically, the North Atlantic route has been considered passable only from the Paleocene to early Eocene. Recent geological and palaeoclimatological evidence, however, suggests that waterways that now prevent terrestrial dispersal via the North Atlantic (e.g., the Fram Strait, Barents Sea) were shallow until the Miocene and, potentially, bridged by seasonal sea ice as early as the late Eocene. We therefore hypothesize that rhinocerotid and ursid dispersal between Europe and North America post-Eocene may have occurred via the North Atlantic. Our study reveals the complex history of two charismatic mammalian clades and provides insight into the importance of the Arctic as a persistent connector of otherwise geographically disparate faunas.