Taxonomic and ontogenetic diversity of Dinomyidae (Rodentia) from the late Miocene-early Pliocene of La Pampa province (Argentina) based on cranio-dental remains

Abstract

Dinomyidae is a clade of caviomorph rodents that include medium to gigantic forms. They are represented by a single living species, Dinomys branickii, distributed from Venezuela to Bolivia in forested regions. However, in the past, they were very diverse. The oldest confident fossil records come from the early and middle Miocene, and during the late Miocene they reached their greatest diversity, reducing since then. In this contribution, the diversity of late Miocene-early Pliocene dinomyids from the Cerro Azul Formation in La Pampa Province (Argentina) is studied. New craniodental remains of at least three species are reported: Tetrastylus laevigatus, T. intermedius, and Diaphoromys gamayensis. Tetrastylus laevigatus is reported for this region based on abundant material, including a portion of the skull associated with the mandible. The presence of juvenile and adult individuals permitted us to analyze the ontogenetic variability of some traits. The specimens assigned to T. intermedius and D. gamayensis consist of mandibular and lower cheek teeth remains. Based on these new remains, we propose that D. gamayensis and D. fiegi are synonymous, with the priority being D. gamayensis. Considering the findings in each faunal association from the Cerro Azul Formation, representatives of T. laevigatus were registered in Salinas Grandes de Hidalgo, Algarrobo del Águila, Victorica, Bajo Giuliani, Laguna Chillhué, and Telén; T. intermedius was recorded in Caleufú. One new specimen of D. gamayensis from Guatraché (species originally described from Gamay) add information about its distribution. Finally these records are added to that of T. araucanus, previously described for Toay. This association suggests the existence of biogeographic connections with regions from northwestern Argentina during the late Miocene.