An exceptionally well-preserved fossil rodent of the South American subterranean clade Ctenomys (Rodentia, Ctenomyidae). Phylogeny and adaptive profile

Ctenomys, the only living Ctenomyidae, is the most diverse genus of hystricomorph rodents. Here, a new extinct species from the Middle Pleistocene of central Argentina is described. It is represented by the most complete skeleton for an extinct Ctenomys species. We analyze its remains and phylogenetic position in the context of other extinct and living Ctenomys species. Additionally, we present an updated and exhaustive timetree of the genus, and include the new species into a matrix of variables with morphofunctional significance. In the parsimony phylogenetic analysis, dagger C. uquiensis, dagger C. chapalmalensis, dagger C. rusconii, and dagger C. thomasi were placed at the base of the Ctenomys total clade, while dagger Ctenomys sp. nov. was the sister species of the crown group. Within the crown Ctenomys, a polytomy was obtained in the basal node formed by dagger C. dasseni, dagger C. kraglievichi, the clade dagger C. viarapaensis-C. osvaldoreigi, the frater species group, and the major clade consisting of the remaining eight species groups. The Bayesian tipdating analysis provided divergence estimates of 4.3 and 1.8 Ma for the origin of the genus and the crown clade, respectively. In the adaptive morphospace, the new species was located in the quadrant of lower scratch- and tooth-digger specialization, close to C. pulcer, a species currently distributed in semi-fixed dunes, pointing to the requirement of similar soil conditions. Finally, the new species co-occurs with dagger C. kraglievichi, a crown-group member with pronounced tooth-digging specialization, suggesting that Ctenomys experienced both significant cladogenesis and substantial eco-morphological diversification during the Middle Pleistocene.