Late middle to late Pleistocene paleoecology and paleoenvironments in the coastal plain of Rio Grande do Sul State, Southern Brazil, from stable isotopes in fossils of Toxodon and Stegomastodon

Stable isotopes (δ13C, δ18O) in teeth of extinct mammals have been used as indicators of diets and climate conditions, which in turn are used for paleoenvironmental reconstructions. The first analysis of stable isotopes in Pleistocene mammals from Southern Brazil is reported here. The analyzed taxa were the notoungulate Toxodon and the proboscidean Stegomastodon from Late Middle to Late Pleistocene fossiliferous beds exposed along Chuí Creek, in the coastal plain of Rio Grande do Sul State. The δ13C isotopes indicate that Toxodon was a mixed-feeder that fed mostly on C4 plants, while Stegomastodon was a browser to mixed-feeder with preference for C3 plants, with less C4 plants in the diet compared to modern African elephants. Comparison with carbon isotopic values in fossils of these taxa from other Late Quaternary localities in South America shows an increased proportion of C3 plants in the diets of both Toxodon and Stegomastodon in higher latitudes. The values of δ18O in both taxa seem to reflect the isotopic composition of the ingested water rather than the isotopic content in the plants of which they fed on, and the observed variations are likely to mirror variations of the patterns of precipitation. Paleoclimatic inferences and possible causes for the (pseudo)extinction of these taxa in southern Brazil are also discussed.