A new genus and species of octodontid rodent from the hilly Chaco of central Argentina (Rodentia: Octodontidae)

Octodontidae is a moderately speciose family (seven genera and 16 species) of South American caviomorph rodents; however, from an ecological point of view, it is a diverse clade that includes terrestrial, cursorial, scansorial, and fossorial to strictly subterranean forms. Its distribution is mostly restricted to the western portion of southern South America, on both sides of the Andes. Here we describe a new living genus and species of Octodontidae, whose distribution is restricted to the Sierra de Guasapampa (central Argentina).

Phylogenetic analysis of mitochondrial molecular markers (cytochrome b) recovers this taxon as sister to Octomys; the genetic distance observed between them is similar to the range of distances found between other genera of Octodontidae (> 9 %). This, together with its morphological divergence from Octomys in the context of Octodontidae, supports its treatment as a separate genus. This rodent is characterized by a unique combination of morphological features, including a long and very hairy tail; grayish brown dorsal coloration, which contrasts against the whitish belly; robust skull, with a proportionally short rostrum; wide interorbital region, with slightly divergent supraorbital edges; proportionally wide incisive foramina; orbitosphenoid with its origin displaced to the basisphenoid; inflated but small auditory bullae; median lacerate foramen not covered by the bulla; and upper molariform lobes with acuminate labial tips.

Specimens of the new genus and species were captured on rocky slopes with abundant bromeliad vegetation in the understory. This finding highlights the importance of continuing field research, especially in areas that have not previously been surveyed.