Surameryx

Surameryx is known from the left half of the nearly complete lower jaw, reminiscent of the North American palaeomerycids, which are known from numerous fossils.[2]

The jaw of Surameryx is similar to that of Barbouromeryx in having a premolar row without reduction compared to the molar row; additionally it showed the characteristic "Palaeomeryx fold", a typical molar crest present in various types of primitive ruminants, and a vertical groove on the back or inner surface of the fourth premolar. Surameryx still differs from its relatives in the much wider shape of the molars and premolars, and in its shorter, upward recurved coronoid process; the stylids were also higher than in other related genera.[2]

Surameryx acrensis was first named and described in 2014, based on the fossil jaw discovered in the Madre de Dios Formation extending along the Acre River in the area between Cobija, Bolivia and Assis Brasil. Surameryx is a representative of the palaeomerycids, an extinct family of Miocene artiodactyls related to cervids and giraffids. More specifically, Surameryx was a member of the dromomerycines, a group of palaeomerycids endemic to North America; within these, it seems to have a close relationship with Barbouromeryx trigonocorneus, a primitive dromomerycine of the middle Miocene (20–16 million years ago).[2] The name Surameryx is derived from the Spanish word sur, "south" and the Greek meryx, "ruminant"; the species name acrensis refers to the Acre River.[2]

The discovery of a dromomerycine in South America is exceptional; until 2014 there were only sporadic findings of placental mammals other than xenarthrans or meridiungulates in South America in layers earlier than the Pliocene epoch. While the Great American Biotic Interchange is traditionally regarded as an event of the late Pliocene (about 3 million years ago), it actually started much earlier, going back at least to the late Miocene, about 10 million years ago.[2] The presence of Surameryx in the Amazon basin is evidence of this exchange in the Miocene, which had already been suggested by the presence of contemporary specimens of gomphotheriids (Amahuacatherium),[3][4] peccaries (Sylvochoerus and Waldochoerus) and tapirs[5] and presence around the same time of ground sloths in North America (Thinobadistes and Pliometanastes).[6] It seems that the paleomerycids were unable to successfully colonize South America, while other groups fared better there. Proboscideans survived until the arrival of humans[7]) and peccaries and tapirs currently live in South America.[2] However, the dating of the putative Miocene fossil beds in western Amazonia and the identification of the gomphothere remains as Amahuacatherium have been challenged.[8][9][10][11]