A new Echimyidae (Rodentia, Hystricomorpha) from the late Miocene of southern South America

Abstract

A new genus of echimyid rodent, yUllumys, from the uppermost Miocene of northwestern Argentina is described. It includes two species, yU. pattoni, sp. nov., and yUllumys intermedius, nov. comb. yUllumys pattoni is known from a skull fragment and the corresponding right hemimandible coming from levels of Loma de Las Tapias Formation, underlying a tuff dated at 7.0 § 0.9 Ma (Huayquerian age, San Juan Province). yUllumys intermedius is represented by a left hemimandible from the ‘Araucanense’ of Valle de Santa Mar ıa (Huayquerian age, Catamarca Province). A phylogenetic analysis in the context of octodontoids linked yUllumys to the clade subtended by the extinct echimyids yPampamys and yEumysops and the living Thrichomys. yUllumys has a peculiar craniomandibular morphology, shared only with yEumysops among the Octodontoidea, involving specializations to open environments such as large and posteriorly extended orbits and related low mandibular condyles. Phylogenetic relationships of yUllumys support the hypothesis that echimyids recorded since the latest Miocene in southern South America, and linked to those currently inhabiting Brazilian open biomes, represent a marginal sample of the great diversity evolving primarily in northern tropical areas