December in Moscow, and the temperature drops under 15 degrees below zero. The radiators in the bar have grown cold, so I sit in a thick coat and gloves drinking vodka while I ponder the fossil birds. The year is 2001, and Evgeny N. Kurochkin of the Russian Academy of Sciences and I have just spent hours at the paleontology museum as part of our effort to survey all the avian fossils ever collected in Mongolia by joint Soviet-Mongolian expeditions. Among the remains is a wing unearthed in the Gobi Desert in 1987. Compared with the spectacularly preserved dinosaur skeletons in the museum’s collections, this tiny wing—its delicate bones jumbled and crushed—is decidedly unglamorous. But it offers a strong hint that a widely held view of bird evolution is wrong.
More than 10,000 species of birds populate the earth today. Some are adapted to living far out on the open ocean, others eke out a living in arid deserts, and still others dwell atop snow-capped mountains. Indeed, of all the classes of land vertebrates, the one comprising birds is easily the most diverse. Evolutionary biologists long assumed that the ancestors of today’s birds owed their success to the asteroid impact that wiped out the dinosaurs and many other land vertebrates around 65 million years ago. Their reasoning was simple: although birds had evolved before that catastrophe, anatomically modern varieties appeared in the fossil record only after that event. The dawning of ducks, cuckoos, hummingbirds and other modern forms—which together make up the neornithine (“new birds”) lineage—seemed to be a classic case of an evolutionary radiation in response to the clearing out of ecological niches by an extinction event. In this case, the niches were those occupied by dinosaurs, the flying reptiles known as pterosaurs and archaic birds.