Paleobiology and paleoecology of ungulates from the Miocene of South America based on an ichnological analysis

Abstract

We analyze fossil footprints and trackways from the middle to late Miocene Vinchina Formation of La Rioja Province, northwestern Argentina. Ichnofossils are preserved in floodplain deposits of anastomosing and meandering fluvial systems and in ephemeral lake facies deposited under arid and semi-arid conditions. The tridactyl ungulate tracks are assigned to the novel ichnotaxa, Macrauchenichnus troyana and Llastaya yesera. Based on comparisons with phylogenetic character states observable on the postcrania of functionally tridactyl ungulates, the trackmaker of M. troyana was a litoptern macraucheniid whereas early toxodontids produced L. yesera. Based on the isometric relationship of footprint area and body mass in modern unguligrade mammals, we propose body mass estimate for these extinct ungulates. Facies analysis of this fossil footprint assemblage reveals that this previously undocumented fauna inhabited mixed grassland-woodland ecosystems developed under warm and seasonal climates in mid-palaeolatitudes. Findings support the idea of a faunal link between high and low latitude ecosystems of South America during the middle to late Miocene.