About the alleged record of the Rheidae Diogenornis in the Cenozoic of Argentina: new interpretations

Abstract

A tibiotarsus (MACN-A 12195) collected by Ameghino in the Sarmiento Formation (Eocene–lower Miocene) outcropping in the ‘Río Chico locality’ (Chubut Province, Argentina) assigned to Diogenornis (Rheiformes, Palaeognathae), and a second limb bone (MPEF-PV 1411) from early Miocene levels of the Sarmiento Formation in Bryn Gwyn (Chubut Province, Argentina) assigned to a bird that resembles Diogenornis, were re-examined here. After a thorough comparison, we established that MACN-A 12195 corresponds to an indeterminate Palaeognathae morphologically close to Rheidae, Struthionidae, and Casuariidae, whereas MPEF-PV 1411 belongs to a Sphenisciformes, probably Palaeospheniscus. The presence of Diogenornis outside of Brazil cannot be confirmed, and therefore, its biochron and distribution area should be still restricted to the early Eocene of Itaboraí (Brazil).