First Steps
Modern science investigates the initial stages of how fossils form
By Sid Perkins
Imagine that during a tour of the paleontology wing of a museum, a group stops to gaze upon a 150-million-year-old fossil of Archaeopteryx, the world’s first bird. “Only 10 of these have been discovered since the species was first described in 1861,” says the guide. “Amazing,” a tourist marvels. “I wonder why there are so few.” Simultaneously, a paleontologist standing nearby is thinking, “I wonder why there are any at all.”
Archaeopteryx fossils may be rare, but those that scientists have collected preserve the ancient creature intact, or nearly so. The creature’s delicate skeleton and feathers show up clearly. They’re encased in limestone presumably derived from the layered, fine-grained sediments that accumulated on the bottom of an ancient lake. But modern birds don’t usually end up in peaceful repose on lake bottoms. If the birds die over water, their light carcasses typically float until they rot. Now, researchers who’ve conducted field experiments with a couple-dozen dead birds and a little mud say that they’ve come up with a scenario that may explain how such fossils get their start.