More than 100 million years ago, dinosaurs roamed Maryland. So did our ancestors — small mammals the size of squirrels or badgers — and the flying reptiles known as pterosaurs.

Amazingly, the footprints of all these creatures of the Cretaceous era were preserved on a single 8.5-foot-long slab of sandstone unearthed on the grounds of NASA’s Goddard Spaceflight Center in Greenbelt, Md., not far north of the nation’s capital.

“It’s unusual to have such a large concentration of different kinds of tracks and small tracks in such a small space,” said Martin Lockley, an emeritus geology professor at the University of Colorado Denver who studied the tracks.

Dr. Lockley and his colleagues described the findings in an article published Wednesday in the journal Scientific Reports. The slab offers unique insights into the behavior of dinosaurs and early mammals; possibly some of the dinosaurs were looking to make a meal of the mammals.