Mesozoic aviary takes form

Abstract

When I attempted a modern synthesis of avian evolution in 1980 (1), I told the then science editor at Harvard University Press that I thought the information on avian evolution was coming in so sluggishly that there would be little need for a quick revision. Was I ever wrong! By the early 1980s, the revelation of the presence of volant paleognaths in the Northern hemisphere Paleogene (2) provided compelling evidence that ratites were not ancient passengers on drifting continents, but the product of a post-Cretaceous–Tertiary radiation from ancestors that for the most part flew to their respective continents. In the same year, an initially muted epiphany appeared with the dramatic discovery by Cyril Walker (3) of the existence of a completely unknown subclass of Mesozoic birds, which he called the enantiornithines, or opposite birds, so-called because the fusion of their tarsal elements was the opposite of that of ornithurine (modern-type) birds; they also possess a distinctive arrangement of the bones of the shoulder girdle and a unique sternum. The story of Mesozoic birds became complicated by the discovery in 1985, by Russian colleague Evgeny Kurochkin (4), of Ambiortus , a Lower Cretaceous archaic but modern-type ornithurine (carinate) bird with an advanced flight apparatus. However, Walker's discovery was followed by the discovery of additional enantiornithine or opposite birds from the Lower Cretaceous of Spain (5). In addition, at the 1992 meeting of the Society of Avian Paleontology and Evolution in …