Global evolution of Equidae and Gomphotheriidae from South America

The contemporary South American mammalian communities were determined by the emergence of the Isthmus of Panama and by the profound climatic oscillations during the Pleistocene.Horses and gomphotheres were 2 very conspicuous groups of immigrant mammals from North America that arrived in South America during the Pleistocene.The present study compiles updated data on the phylogeny,systematics and ecology of both groups in South America.The horses in South America are represented by 2 genera,Hippidion and Equus,as are the gomphotheres,represented by Cuvieronius and Stegomastodon.Both genera of horses include small(Hippidi­on devillei,H.saldiasi,E.andium and E.insulatus)and large forms(Equus neogeus and H.principale),which dispersed into South America using 2 different routes.The possible model for this dispersion indicates that the small forms used the Andes corridor,while larger horses dispersed through the eastern route and through some coastal areas.In the case of gomphotheres,Cuvieronius and Stegomastodon reached South America in 2 inde­pendent dispersal events,and Cuvieronius dispersed across the Andean corridor,while large Stegomastodon spread along the eastern route.Horses and gomphotheres present values ofδ^(13)C from woodlands to C4 grass­lands.Hippidion present lower values ofδ^(13)C than Equus in the late Pleistocene,whereas the gomphotheres di­verge from value ofδ^(18)O,reflecting that Cuvieronius inhabited the Andean corridor and Stegomastodon dis­persed through eastern plains.The gomphothere and horse species recorded in South America became extinct around the time that humans arrived.