Diversity of the Pleistocene Gomphotheres (Gomphotheriidae, Proboscidea) from South America

The gomphotheres were recorded in South America from the early Middle Pleistocene (Ensenadan Land-mammal Age) to the latest Pleistocene (Lujanian Land-mammal Age). They were descendants of the gomphothere stock that originated in North America and arrived to South America during the ‘Great American Biotic Interchange’. Only two genera are recognised: Cuvieronius with only one species (Cuvieronius hyodon), and Stegomastodon with two species (Stegomastodon waringi and Stegomastodon platensis). Two corridors would have developed during the Pleistocene in South America. These two corridors have conditioned the paleobiogeographic history of most North American mammals in South America. In fact, different models can be postulated for different groups depending on their capacity to produce distinct adaptive types throughout the duration of their dispersion process. In the case of South American gomphotheres, the small Cuvieronius utilised the Andean corridor, whereas the larger Stegomastodon dispersed through the eastern route. Cuvieronius hyodon is geographically restricted to the Andean Region in Ecuador, Peru, Bolivia, Chile and Northwestern Argentina, it inhabited an arid landscape. Cuvieronius from Tarija indicated that they were almost exclusively mixed-feeders. This species seems to have been adapted to a temperate-cold climate, since in the inter-tropical zones it has been only found at the highest levels, while in Chile it expanded to the littoral zone, that surely offered similar living conditions, in terms of temperature as the Andes corridor. Stegomastodon waringi was recorded in the Santa Elena peninsula in Ecuador, and in Brazil. S. waringi from the Peninsula of Santa Elena, shows an adaptive trend of mixed-feeder to grazer. Stegomastodon platensis was recorded in the Middle to latest Pleistocene of Argentina, especially the Pampean Region, and also during Late Pleistocene in Uruguay and Paraguay. S. platensis from the Middle Pleistocene of Argentina shows mixed-feeder to browser feeder adaptations. Stegomastodon seems to have predominated in lower latitudes, where it would occupy savannahs or xerophytic pasture areas, and consequently it would be better adapted to warm or temperate climatic conditions. Their most austral distribution does not surpass the 37th parallel in the Buenos Aires province. The frequency of Stegomastodon platensis diminishes in the Pampean Region by the latest Pleistocene, when environmental conditions became colder and drier.