The Eocene armadillo Utaetus buccatus (Euphractinae) in the Guabirotuba Formation (Curitiba Basin) and carapace morphological implications

Abstract

The Guabirotuba Formation belongs to a small sedimentary basin located in the southernmost portion of the Cenozoic continental rift system of southeastern Brazil. In this unit was recognized the Guabirotuba Fauna from Eocene, that includes several cingulates such as Machlydotherium, Proeocoleophorus, Parutaetus, Meteutatus, Utaetus and an indeterminated Astegotheriini. The genus Utaetus in the Guabirotuba Fauna is confirmed by presence of Utaetus buccatus based on the specimen MCN.P.1231 and reinforce the Barrancan Age for the Guabirotuba Formation. In this study we analyzed numerous osteoderms associated to an individual, representing most of the external morphological diversity among fixed, semi-movable and movable osteoderms. Morphological features are described for fixed and movable osteoderms as well as, for the first time, for the semi-movable osteoderms. Features of some semi-movable osteoderms indicate the presence of some kind of pectoral buckler on Utaetus buccatus. The known geographic distribution of the genus Utaetus includes Argentinian Patagonia, Northwest of Argentina, and South of Brazil. The geographic distribution of the species Utaetus buccatus, previously restricted to Argentinian Patagonia, is here expanded to lower latitudes during the middle Eocene, which allow to infer that the species distribution was wider than previously thought.