The genus Oligosarcus consists of 16 previously described species (Menezes, 1969a; Menezes, 1987; Miquelarena & Protogino, 1996), distributed throughout most of the main hydrographic systems of cisAndean South America below 14º of latitude (Menezes, 1988). This wide distributional range includes the Bolivian and Argentinean Andean highlands, the Brazilian crystalline shield, and the Atlantic slope drainages of eastern and southern South America (Menezes, 1988). Species of Oligosarcus are typically small-to medium sized predators on arthropods and other fishes, inhabiting mainly smaller tributaries of the main river basins (Menezes, 1969b; Aranha et. al, 1998; Casatti, 2003; Hermes-Silva et al., 2004).
Menezes (1987) provided a comprehensive review of the previous known species and described three new ones. The latest addition to the genus was made by Miquelarena & Protogino (1996) in describing Oligosarcus menezesi . No intraspecific phylogenetic information on this genus has been already provided; however, the presence of tricuspid teeth along most of ectopterygoid length, a unique feature among a set of genera presently assigned as incertae sedis in Characidae (Lima et al, 2003), suggests that the genus consists of a monophyletic group. The phylogenetic relationships and biogeography of Oligosarcus are currently under study by one of the authors (ACR).
