Late Miocene crocodylians from northeast Argentina: new approaches about the austral components of the Neogene South American crocodylian fauna

The richest and more explored regions concerning Miocene crocodylians in South America are the basins surrounding the areas of Urumaco (Venezuela), La Venta (Colombia), Acre (Northwest Brazil) and Paraná (Northeast Argentina). Fossils from the late Miocene in the Paraná area were recovered from the “Conglomerado Osífero” (Ituzaingó Formation) and assigned to several taxa of Caimaninae (Alligatoroidea) and to a taxon of Gavialoidea. The late Miocene “fauna” of crocodylians recorded in northeast Argentina differs from coeval ones of northern South America by the absence of crocodyloids, some alligatorid genera (such as Purussaurus, Melanosuchus, and Paleosuchus) and by the scarce gavialoid species. Giant forms, conspicuous in the northern South American deposits, are also absent in southern latitudes. Despite this, the austral South American crocodylian fauna exhibits strong affinities with the northern, contemporary forms, sharing taxa at generic (i.e. Caiman and Gryposuchus) and even specific levels (i.e. Mourasuchus nativus). The sharing of such freshwater taxa in the Miocene indicates partial connections of drainage basins through swamp areas on their boundaries, and is evidence against the assumption of an intracontinental coeval seaway link in this continent proposed by several authors.