Since the last of the non-avian dinosaurs died out 65 million years ago during the mass extinction that closed the curtain on the Cretaceous period, birds have evolved other characteristics that set them apart from dinosaurs. Modern birds have higher metabolisms than even the most agile Velociraptor ever had. Teeth disappeared at some point in birds' evolutionary history. Birds' tails got shorter, their flying skills got better and their brains got bigger than those of dinosaurs. And modern birds, unlike their Maniraptoran ancestors, have a big toe that juts away from the other toes, which allows birds to perch. "You gradually go from the long arms and huge hands of non-avian Maniraptorans to something that looks like the chicken wing you get at KFC," says Sues. Given the extent of these avian adaptations, it's no wonder the evolutionary link between dinosaurs and birds as we know them remained hidden until paleontologists started analyzing the rich fossil record from China.
Chaoyang is a drab Chinese city with dusty streets; in its darker corners it's reminiscent of gritty 19th-century American coal-mining towns. But to fossil collectors, Chaoyang is a paradise, only a one-hour drive from some of the Yixian Formation's most productive beds.
One street is lined with shops selling yuhuashi, or fish fossils. Framed fossils embedded in shale, often in mirror-image pairs, can be had for a dollar or two. A popular item is a mosaic in which a few dozen small slabs form a map of China; fossil fish appear to swim toward the capital, Beijing (and no map is complete without a fish representing Taiwan). Merchants sell fossilized insects, crustaceans and plants. Occasionally, despite laws that forbid trade in fossils of scientific value, less scrupulous dealers have been known to sell dinosaur fossils. The most important specimens, Zhou says, "are not discovered by scientists at the city's fossil shops, but at the homes of the dealers or farmers who dug them."
In addition to Sinosauropteryx, several other revelatory specimens came to light through amateurs rather than at scientific excavations. The challenge for Zhou and his colleagues is to find hot specimens before they disappear into private collections. Thus Zhou and his colleague Zhang Jiangyong, a specialist on ancient fish at IVPP, have come to Liaoning province to check out any fossils that dealers friendly to their cause have gotten their hands on of late.
Most of the stock in the fossil shops comes from farmers who hack away at fossil beds when they aren't tending their fields. A tiny well-preserved fish specimen can yield its finder the equivalent of 25 cents, enough for a hot meal. A feathered dinosaur can earn several thousand dollars, a year's income or more. Destructive as it is to the fossil beds, this paleo economy has helped rewrite prehistory.
Zhou picks up a slab and peers at it through his wire-rimmed glasses. "Chairman, come here and look," Zhou says to Zhang (who earned his playful nickname as chairman of IVPP's employees union). Zhang examines the specimen and adds it to a pile that will be hauled back to Beijing for study—and, if they are lucky, reveal another hidden branch of the tree of life.
Richard Stone has written about a Stonehenge burial, a rare antelope and mysterious Tibetan towers for Smithsonian.