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

The caviomorph rodent family Dinomyidae, represented today by <i>Dinomys branickii</i>, has a fossil record dating back to the Early Miocene, and an outstanding diversity during the Late Miocene-Pliocene. <i>Telicomys</i> 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 with precise stratigraphic provenance, with a partially preserved cranium, mandible and vertebrae, allowed the unprecedented assessment of associated upper and lower dentition of <i>Telicomys</i>, supporting the synonymy of <i>‘Telicomys gigantissimus’</i> with <i>Telicomys giganteus</i>. Elements of the holotype of <i>‘Tl. gigantissimus’</i> are here described for the first time. We analysed <i>‘Telicomys’ amazonensis</i> from the Late Miocene of Brazil and concluded that it does not belong to <i>Telicomys</i>. For <i>Tl. giganteus</i>, 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 <i>Dinomys</i>. Our phylogenetic analysis places <i>Telicomys</i> as closely related to the species of <i>Tetrastylus</i> (<i>Tt. laevigatus</i>, <i>Tt. intermedius</i>), indicating that the linage including <i>Dinomys</i>, <i>Tetrastylus</i> and <i>Telicomys</i> originates at least as early as the Late Miocene.