Note On Rheiformes (Aves: Palaeognathae) From A Quaternary Cave In The Lagoa Santa Karst, Eastern Brazil

Rheiformes are a South American lineage of large, flightless palaeognathous birds, currently represented by the genus Rhea and the two extant species R. americana and R. pennata. The fossil record of the group extends back to the Eocene, with its greatest diversification occurring during the Neogene. During the Quaternary, Rheiformes were widely distributed across southern and central South America. The Lagoa Santa region is particularly notable for its rich paleontological and archaeological record. Quaternary records of Rheiformes from caves in this region provide important evidence for understanding the distribution of the group in Brazil, although their chronological context remains uncertain owing to the absence of direct dating. Here, we describe and illustrate two rheiform bones recovered from a cave in the Lagoa Santa karst region. The material comprises a partially complete tibiotarsus and a fragmented tarsometatarsus, interpreted as belonging to a single individual. Comparative anatomical and morphometric analyses support their attribution to Rhea americana, based on morphological features and dimensions consistent with adult specimens of the species. This occurrence extends the Quaternary record of Rheiformes in the Lagoa Santa region and contributes to the fossil and subfossil record of Rhea in Brazil. The absence of stratigraphic and geochronological control precludes a precise age determination. Although the association with an extinct dasypodid indicates the presence of Late Pleistocene or Early Holocene faunal elements at the locality, a Holocene or even recent age for the rheiform remains cannot be excluded.