One hundred and twenty million years ago, there was a crystal-clear lake nestled in what is now northwestern China. Soaring trees hugged the shoreline. The air was filled with prehistoric birdsong. And there, floating along in the water, was a pigeon-sized, loon-like bird known as Brevidentavis zhangi. When the bird died, its body drifted down to the lakebed. Over thousands and thousands of years, layers of sediment covered the bird’s body. The lake dried up. The bird’s fragile, delicate bones fossilized into rock. And there it waited—until the summer of…
