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

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.