Revisiting the evolutionary history and paleobiogeography of fossil horses from South America

Horses are a conspicuous group of immigrant mammals from North America that arrived in South America during the late Pliocene and no survived the megafaunal extinction, approximately ten thousand years ago. Two main equids lineages are found in South America. The first lineage is the species assigned to Equus, which appears during the middle Pleistocene and shows horse-like anatomical features. The second lineage is the genus Hippidion, which were horses with very distinctive anatomical features are recorded for the first time during the late Pliocene. The predominance of the dispersal events over vicariant ones is consistent with the migratory habits of horses. The global biogeographic distributions of horses explain the mode of dispersal and their migration from North America to another continent. The dispersal and the diversification process in small to middle size species (Equus andium, Equus insulatus, Hippidion devillei, and Hippidion saldiasi) occurred through the Andes corridor whereas the large species (Equus neogeus and Hippidion principale) mainly traveled using the eastern plain route. The pathway of dispersion in each species reflects its adaptive change and habitat preference. The present study aims to provide a synthesis of already published data on the phylogeny, systematics, palaeobiogeography and palaeoecology of both the lineages recorded in South America, updating some taxonomic data.This work has been made possible thanks to Research Project ANPCYT PICT 2015-1512 to JLP; DGICYT CGL2016-79334-P from Spain to MTA; and Grant of the National University of Central Argentina (UNICEN) to JLP