Geographic distribution is basic information on the biology for any species. However, the precise data on spatial limits of species are unavailable for most taxa, but knowledge of such data is essential for their conservation and monitoring. We report the northernmost records of Inia araguaiaensis, a newly described river dolphin that occurs in the Araguaia and Tocantins Rivers, in central-eastern Brazil. Three stranded specimens were collected in Marajo´ Bay area and were identified as I. araguaiaensis based on mitochondrial DNA analysis. We assume that these records represent not only a range expansion of nearly 500 km north from the previous known limit of I. araguaiaensis, but also a potential evidence on species-level responses to changes in habitat, as a result of adaptability to variable environmental conditions. These new records based on stranded animals reveal the importance of sampling effort in remote areas, such as coastal waters of the Amazon estuary ecosystem, and help to establish the actual distribution limits of this aquatic mammal for conservation purposes.
