Perimys

Perimys is an extinct genus of neoepiblemid rodent that lived from the Early to Late Miocene in what is now South America. Fossils have been found in the Cerro Bandera, Cerro Boleadoras, Ituzaingó, Santa Cruz, and Sarmiento Formations of Argentina, and the Galera, Santa Cruz, and Río Frías Formations of Chile.

Description

Perimys was a medium to large-sized rodent. Perimys can be distinguished from other caviomorphs in having euhypsodont and bilophodont cheek teeth, with the hypoflexus/id being conspicuously broader and filled with more cementum than in Prolagostomus and Pliolagostomus. As a result, the teeth of Perimys have a U-shape occlusal outline.

The malleoincudal complex of Perimys indicates its head was elongated, but not to the same extent as in chinchillines. As in chinchillids, however, the incudal long process of Perimys is more prolonged by a slight amount than the short process.

Taxonomy

Perimys was first described by Florentino Ameghino in 1887 based on remains found in the Santa Cruz Formation of Argentina, with the proposed type species being Perimys erutus. Several other species have been described as pertaining to this genus. Ameghino originally assigned it to the obsolete family Eryomyidae, however, many later authors have assigned it to the Neoepiblemidae family.

The following cladogram of the Caviomorpha is based on Busker et al. 2020, showing the position of Perimys.

Palaeobiology

Functional analysis of its scapula, humerus, ulna, and radius suggests that Perimys would have been well adapted for fossoriality.