The caviomorph rodents are scarcely known from the Quaternary record of Rio Grande do Sul State, Brazil. This work deals with caviomorphs from two sites, with datings including the Early to Late Holocene. The taxa recorded were: Cavia sp., C. aperea, C. magna, Ctenomys sp., Phyllomys sp., Myocastor coypus, Euryzygomatomys mordax, Dicolpomys fossor, the last two of which are extinct. A new fossil species, Clyomys riograndensis sp.nov. is also described. The stratigraphic distribution of these taxa allows us to suggest a slow and gradual climatic change during the Holocene and a mosaic environment with grasslands and gallery forests, which is indicated by the presence of fossorial animals that typify open areas, coexisting with taxa of forested areas.

SMALL MAMMALS DIVERSITY (DIDELPHIMORPHIA AND RODENTIA) FROM THE HOLOCENE OF NORTHEASTERN RIO GRANDE DO SUL STATE, SOUTHERN BRAZIL: TAXONOMIC AND PALEOENVIRONMENTAL IMPLICATIONS. Despite the increase in knowledge about small mammals from the Holocene of Rio Grande do Sul State and their importance as paleoenvironmental indicators, most assemblages from archaeological sites remains without a detailed analysis. This paper studies the rich small mammals content recovered from the archaeological site RS-C-61: Adelar Pilger, Harmonia, which shows evidence of continuous human occupation throughout the Holocene, from about 8,000 years BP to 3,000 years BP. The assemblage of this site is composed of 25 taxa, including fi ve didelphid marsupials, 15 cricetid and fi ve caviomorph rodents. Most marsupials are also registered in two other sites, Afonso Garivaldino Rodrigues and Sangão. Among Cricetidae, Gyldenstolpia, Kunsia and Oxymycterus are fi rst recorded for Quaternary of Rio Grande do Sul State. On the other hand, the caviomorph assemblage of Pilger site is less diverse than those of the Afonso Garivaldino Rodrigues and Sangão sites. Pilger site includes both small mammals of open (e.g. Thylamys, Calomys, Cavia) and forest (Delomys, Sooretamys and Phyllomys) environments, also supported by palynological data. Three caviomorph (Euryzygomatomys mordax, Dicolpomys fossor and Clyomys riograndensis) are extinct and, compared to the recent fauna of seasonal forest of Rio Grande do Sul, three other taxa (Gyldenstolpia sp., Kunsia tomentosus and Pseudoryzomys simplex) suff ered regional extinctions.

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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 Sanga˜o. 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.