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

A tibiotarsus (MACN-A 12195) collected by Ameghino in the Sarmiento Formation (Eocene-lower Miocene) outcropping in the 'Rio 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 Itaborai (Brazil).

Automated summary

This article re-examines two fossils, one belonging to the Palaeognathae group and the other possibly to the Sphenisciformes group. The study suggests that the presence of Diogenornis is currently limited to the early Eocene of Brazil.