The effect of paleoecology and paleobiogeography on stable isotopes ofQuaternary mammals from South America

The modern South American mammalian assemblage was determined by the closure of the Panamaisthmus (~2.7 -3.1 Ma) and later on, by profound climatic and environmentalfluctuations occurredduring the Quaternary as well as by the appearance of humans in the continent. In the present study,stable isotope analyses (δ13C, δ18OCO3 and δ18OPO4) have been carried out on Pleistocenee Holocene northern inmigrant and endemic taxa from a broad latitudinal and altitudinal distribution in SouthAmerica with the purpose of characterizing their paleoecology and the effects of the paleobiogeographicdistribution on stable isotope results. Equids and gomphotheres show a wide range of δ13C values goingfrom woodlands to pure C4 grasslands. In the case of equids, Hippidion shows lower δ13C values than Equusin the Late Pleistocene, whereas, in the case of gomphotheres, Cuvieronius and Stegomastodon differ in their δ18O values on account on differences in their paleobiogeography with the former found in the Andean corridor and the latter dispersing through an eastern route. Isotope data of the rest of taxa (immigrant and endemic) are in general in good agreement with other previous isotopic and non-isotopic studies. The latitude threshold between mixed C3-C4 and pure C3 conditions have been pin-pointed at ~33ºS in the Middle and the Late Pleistocene. Mammalian δ18O values are intimately related to latitudinal and altitudinal distribution, with the latter exerting an overriding influence independently of latitude. Calculated altitudinal gradients (between ~0.23 ‰ /100 m and - 0.40 ‰/100 m) are within therange of modern gradients