YANJI, China (AP) — At the end of a street of newly built high-rises in the northern Chinese city of Yanji stands an exposed cliff face, where paleontologists scrape away 100 million-year-old rock in search of prehistoric bones.

Like many fossil excavation sites in China, this one was discovered by accident.

China's rapid city building has churned up a motherlode of dinosaur fossils. While bulldozers have unearthed prehistoric sites in many countries, the scale and speed of China's urbanization is unprecedented, according to the United Nations Development Program.

Perhaps no one has seized the...