The rediscovery of Rhagomys rufescens (Thomas, 1886), with a morphological redescription and comments on its systematic relationships based on morphological and molecular (cytochrome b) characters

Abstract

Rhagomys rufescens is one of the rarest species of the South American mammalian fauna. This scarcity has determined a lack of studies on the natural history and systematic relationships of this presumptive Atlantic forest endemic. Here we report on two recently collected specimens of Rhagomys rufescens, redescribing its morphology and discussing its phylogenetic relationships on the basis of Cytochrome b sequence data. Morphological comparisons with selected Atlantic forest species reveal that R. rufescens displays a remarkably divergent set of character states, such as a unique molar design with diagonally projected cusps and an extremely reduced first digit of hindfoot with a nail instead of a claw, resembling an additional plantar pad. These and other morphological features are suggestive of an arboreal habitus and, at least with respect to its molar morphology, a rather insectivorous diet. Molecular analysis did not allow unequivocal allocation of Rhagomys either to the oryzomyine or to the thomasomyine suprageneric assemblages, as a result of its high level of evolutionary divergence. Rhagomys seems to represent a rather divergent lineage with no clear relation to any extant sigmodontine tribe.