On the morphological, taxonomic, and phylogenetic status of South American Quaternary dinomyid rodents (Rodentia: Dinomyidae)

Abstract

Since the end of the Miocene, South American Dinomyidae rodents have declined in diversity, and are now represented by a single species—Dinomys branickii. The Quaternary fossils of Dinomyidae rodents are very rare, limited to some records from the tropical region of Brazil. One of them is a peculiar taxon described during the 1950s: Tetrastylus walteri. Here, we review the holotype (a dentary with cheek teeth) of this dinomyid and report new specimens, which include a palatal region with upper cheek teeth (previously unknown), contributing to the anatomical knowledge of this extinct rodent. Comparisons demonstrate that this taxon is a valid species, although its generic affinity is still dependent on additional analyses. The other analyzed taxon is Niedemys piauiensis, an enigmatic rodent described based on limited evidence and here interpreted as a possible dinomyid. Further data are necessary to better understand the extinct dinomyids that represent the decline of this particular group of rodents during the Quaternary of South America.