PALEOGENE FOSSILS AND THE RADIATION OF MODERN BIRDS

Abstract

MODERN GENERA OF birds arose mainly in the Neogene Period (1.8-23.8 mya), and modern species mainly in the Plio-Pleistocene (0.08-5.3 mya). Neogene fossil birds generally resemble modern taxa, and those that cannot be attributed to a modern genus or species can usually be placed in a modern family with a fair degree of confidence (e.g. Becker 1987, Olson and Rasmussen 2001). Fossil birds from earlier in the Cenozoic can be more challenging to classify. The fossil birds of the Paleogene (23.8-65.5 mya) are clearly attributable to the Neornithes (modern birds), and the earliest well-established records of most traditional orders and families of modern birds occur then. But the fossils tend to be primitive and more difficult to seat phylogenetically within the Neornithes (Dyke and van Tuinen 2004). Not a few early Paleogene fossils have been said to exhibit a mosaic of characters associated with two or more traditional families or orders (e.g. Peters 1992, Feduccia 1999, Mayr 2003a). An excellent example is an Eocene bird referred to the Psittaciformes that lacks the specialized skull of parrots (Mayr 2005a). Paleontologists sometimes resort to describing primitive fossils as petrel-like or hoopoelike (for instance) without referring them to the corresponding modern families (e.g. Houde and Olson 1992; Feduccia and McPherson 1993; Mayr 2000a, 2003b). Nevertheless, the primitive fossils of the Paleogene provide the earliest firm records of such diverse modern radiations as ratites (Houde 1988), owls (Mourer-Chauvire' 1987, Peters 1992), waterfowl (Ericson 1997, Olson 1999, Dyke 2001), ibises (Peters 1983), penguins (see Clarke et al. 2003), galliforms (Mourer-Chauvire 1992, Mayr 2000b, Dyke and Gulas 2002), passerines (Mourer-Chauvire et al.