New records of Equus and Hippidion (Mammalia, Perissodactyla) from the Late Pleistocene of the Salado River (Buenos Aires province, Argentina)

The sedimentary sequences exposed along the banks of the Salado River (Buenos Aires province) preserve an important Late Pleistocene Megafauna. This paper describes new specimens of Hippidion and Equus from a Late Pleistocene locality near Junin City at the middle course of the Salado River. The comparative study with other horses from different South American localities, mostly from Argentina and Brazil, allowed identifying the specimens as Equus neogeus, Hippidion principale and Hippidion devillei. The coexistence of three species of the Equidae family at the same locality is found in several locations of South America. This deposit can be referred to as the biozone of Equus neogeus, which constitutes the biostratigraphic basis for the Lujanian stage/age. In the Pampean region, the Lujanian is considered to begin with interglacial conditions (EI 5e, 130 ka BP). At the same time, its final part coincides with the Last Glacial Maximum (ca. 18 ka BP), including the last glacial advance (13-11 ka BP). During these time intervals, fauna adapted to arid and cold conditions predominates that were compatible with the coexistence of three species of horses. Taxonomic implications of this finding and some regional paleoenvironmental history are discussed.