MESOZOIC BIRDS FROM SOUTHERN PATAGONIA SHED LIGHT ON THE EARLY ANTARCTIC AVIFAUNA

Abstract

The Mesozoic record of birds in Antarctica is still very patchy, restricted to several specimens of derived ornithurine birds (belonging to Neornithes or stem-Neornithes) that come from Upper Cretaceous outcrops on Vega Island. Because this site was geographically isolated from those containing previously known coeval bird assemblages, comparisons were severely restricted. However, in recent years, paleontological research in the Chorrillo Formation (Maastrichtian) outcropping in southern Santa Cruz province has partially filled this geographical gap. The new prospections have yielded a relatively rich bird assemblage, including fossils attributable to Enantiornithes, Hesperornithiformes, and derived Ornithurae. The present contribution aims to compare the Maastrichtian bird assemblages from Santa Cruz (Patagonia) and Antarctica. One of the main differences between the assemblages is that only Neornithes and kin are present in Antarctica, and there are no records of Hesperornithiformes, Enantiornithes, or more basal taxa. This may be explained by Neornithes and kin showing accelerated growth and notably high metabolism, which distinguishes them from the slow and cyclic growth of more basal birds and may have allowed them to survive in the relatively cold Antarctic climate.