New insights on Telicomys giganteus , the last giant dinomyid rodent from the Pliocene of central Argentina

The caviomorph rodent family Dinomyidae, represented today by Dinomys branickii, has a fossil record dating back to the Early Miocene, and an outstanding diversity during the Late Miocene-Pliocene. Telicomys was a giant dinomyid that lived during the Pliocene in southern South America(Buenos Aires Province, Argentina). The study of a new specimen, the only of this genus withprecise stratigraphic provenance, with a partially preserved cranium, mandible and vertebrae,allowed the unprecedented assessment of associated upper and lower dentition of Telicomys,supporting the synonymy of ‘Telicomys gigantissimus’ with Telicomys giganteus. Elements of theholotype of ‘Tl. gigantissimus’ are here described for the first time. We analysed ‘Telicomys’amazonensis from the Late Miocene of Brazil and concluded that it does not belong to Telicomys. For Tl. giganteus, body mass was estimated between 89 and 143 kg. Its large incisors could be related to feeding strategies and/or intraspecific agonistic behaviour, and its scapular morphology suggests comparable locomotor habits and substrate use with that of Dinomys. Our phylogenetic analysis places Telicomys as closely related to the species of Tetrastylus (Tt. laevigatus, Tt. intermedius), indicating that the linage including Dinomys, Tetrastylus and Telicomys originatesat least as early as the Late Miocene.