Environmental change and marsupial assemblages in Holocene successions of Southern Brazil

In the last few years, studies about climate successions in Rio Grande do Sul State (southern Brazil) during the Quaternary increased significantly, mostly due to palynological studies. The knowledge about Quaternary small mammals from Rio Grande do Sul is very poor. However, among the results obtained by archeological research there is an interesting collection of small mammals exhumated from rock shelter deposits. Here we describe the marsupial fauna found in two sites: Garivaldino and Sangao. Both sites are located at the boundary between two large Neotropical subregions, Chaco and Parana. Sediments from these two sites are from the early, middle, and part of the late Holocene. Additionally, we discuss paleobiogeographic, paleoenvironmental, and paleoclimatic aspects, on the basis of the seven taxa recorded: Gracilinanus microtarsus, G. agilis, Monodelphis americana, Thylamys velutinus, Thylamys cf. T. velutinus, Philander opossum, and Didelphis sp. Paleoenvironmental aspects inferred for both sites are consistent: the emergence of typical elements of the current Parana biogeographic subregion was probably established by the end of the early Holocene or the beginning of the middle Holocene. Conclusions are also coherent with the results previously obtained from palynological sequences in these same localities. The micro-marsupials sequence suggests that the environmental changes were not abrupt but gradual during the Holocene in Rio Grande do Sul State.