The mid-Araguaia River basin in central Brazil is considered a priority area for biodiversity conservation, and Parque Estadual do Cantão (PEC) is one of the most important protected areas in this ecotone between Cerrado and Amazonia. This area suffers an intensive human pressure with high rates of deforestation, and still remains poorly studied in terms of biodiversity. From June 2007 to November 2008 we sampled small mammals from both banks of the mid-Araguaia River, in the states of Tocantins and Pará. Data are given about morphological traits, geographic distribution and natural history of 22 species of small non-volant mammals (eight marsupials and 14 rodents) surveyed at PEC and its surroundings. We also present mitochondrial phylogenetic analyses that allow species identification within the genera: Oecomys, Oligoryzomys and Rhipidomys, and delineate an undescribed species of Thrichomys. Based on morphologic and molecular data, we describe a new species of Rhipidomys previously assigned to R. nitela, which is apparently endemic to the AraguaiaTocantins basin in the Cerrado. Additionally, our phylogenetic analyses provide support for the role played by the Araguaia River as an important geographic barrier for two sister species of Rhipidomys.

Background: Seasonally flooded natural forest fragments, so-called ipucas, in the Araguaia alluvial plain of the state of Tocantins, central Brazil, represent a peculiar landscape that is poorly surveyed. This study considers the diversity in the small mammal assemblage and the zoogeographical patterns of this assemblage when compared to 30 other study sites in Brazil.

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