A new rodent (Caviomorpha: Dinomyidae) from the upper Miocene of southwestern Brazilian Amazonia

Abstract

Recently, the fossil record of rodents from southwestern Brazilian Amazonia has been reviewed with regards to its diversity as well as its ecological relationships. In the reviews, the necessity to report new specimens collected with stratigraphic control was stated. Here, a new dinomyid specimen collected during a 2015 expedition to the Niterói locality, Acre River, is reported. The material is a fragment of skull with the right P4–M1 and the left P4–M2 preserved. The cheek teeth are protohypsodont, a characteristic employed to differentiate Potamarchinae dinomyids from the euhypsodont dinomyids Eumegamyinae and Tetrastylinae. The occlusal surface of the cheek teeth is composed of lophs with interruptions, showing little wear, which suggests that the specimen is not fully ontogenetically developed. The specimen has a unique combination of characters (protohypsodont and pentalophodont cheek teeth, with the leading edges of similar thickness to the trailing edges, and presence of a groove on the bottom of the infraorbital foramen) not present in other known dinomyids, which led us to erect a new taxon. The abundant and diverse fossil record of protohypsodont dinomyids suggests that an important radiative event may have occurred during the middle–late Miocene of northern South America.

http://zoobank.org/urn:lsid:zoobank.org:pub:E082C3C6-47B6-4D83-9009-A64879AAFC7A

http://www.zoobank.org/NomenclaturalActs/16235A7B-A261-445E-8DD4-940AB21DCB06

Keywords:

• Ontogeny
• Niterói locality
• Chinchilloidea
• Potamarchinae
• protohypsodont
• Neogene

Acknowledgments

We would like to express our gratitude to: Fundação de Amparo a Pesquisa do Estado de São Paulo - FAPESP (Process FAPESP 2011/14080-0, Annie S. Hsiou), for financial support during the fieldwork; Max Cardoso Langer, who read and commented the first draft of this work; Pierre-Olivier Antoine and the anonymous reviewer that improved significantly the first draft of this paper; Renata Cunha for the artwork of the rodent here described; Katarzyna Piper, for the English grammar review; TNT v.1.5 was used for phylogenetic analysis; this is a program made freely available thanks to a subsidy by the Willi Hennig Society.