Chronology and ancient feeding ecology of two upper Pleistocene megamammals from the Brazilian Intertropical Region

摘要

In Brazilian Intertropical Region (BIR) fossil remains of the giant ground sloth Eremotherium laurillardi(Lund, 1842) and of the proboscidean Notiomastodon platensis (Ameghino, 1888) are the most abundant among megaherbivores. However, the paleoecology of both species needs to be better understood to enlighten why these species disappear in the end of the Pleistocene, an issue that is still debated. During the last decades, the carbon and oxygen stable isotopes have been increasingly being used to obtain paleoecological information about extinct animals, although this information is in most cases dissociated from chronological data. Thus, the main objective of this study is to contribute to the knowledge about feeding ecology and chronology of E. laurillardi and N. platensis within BIR. For each fossil sample we performed stable isotopes analyses (δ~(13)C/δ~(18)O) and radiocarbon dating (~(14)C with AMS). The results showed that N. platensis occurred between 12,125 and 19,594 cal yr BP and exhibited a grazer diet (δ~(13)C =-1.1&-1.3&), while E. laurillardi lived between 11,084 and 27,690 cal yr BP, with a mixed feeder diet (C_3/C_4 plants; values ratio δ~(13)C = -7.7& to -3.3&). The δ~(18)O values of N. platensis ranged between 2.20& and 3.60&, while the values of E. laurillardi ranged between -3.10& and-1.10&. Neither species did exhibit differences in its diet through time, which suggests that the vegetational composition of this locality did not vary in the late Pleistocene. Both species were living in an open environment, rich in herbaceous plants (C_4 plants) and with tree and shrub with disjoint distribution, maybe similar to some parts of recent Caatinga, where they have partitioned the spatial and feeding niches.