First record of a Notoungulata (Mammalia) from the Late Miocene of Quebrada La Troya, Toro Negro Formation, Vinchina, La Rioja: Taxonomy and aleoecological notes

Abstract

The extinct herbivorous mammals of the order Notoungulata hold significant importance in the South American fossil record, showcasing a wide range of sizes and forms. In La Rioja Province, northwestern Argentina, at the Quebrada La Troya locality, Vinchina Department, the Toro Negro Formation has revealed the first notoungulate remains of a single individual, PULR-V 222. It is identified as Hemihegetotherium achathaleptum (Hegetotheriidae) with an estimated body mass of 18.6–28.9 kg. The Toro Negro Formation has a low proportion of notoungulate fossils compared to other taxa, such as rodents, cingulates, and especially sloths, which differs from other coeval formations. This disparity suggests different environmental conditions during the Late Miocene. The underrepresentation of notoungulates in the Toro Negro Formation may be due to various factors, including ecological conditions and sampling biases, though the latter is not firmly supported. Additionally, PULR-V 222 exhibits hypothesized predation marks, likely made by large vertebrate predators such as the armadillo Macroeuphractus, sparassodonts, or contemporaneous carnivorans. This study emphasizes the need for further exploration in the Toro Negro Formation to better understand the taphonomy and ecological dynamics affecting the notoungulate representation.