Rock of Ages.

• Position: THE BIG PICTURE - Fossil footprints - Brief article

It's as close as we may ever get to a snapshot of Earth before the Ice Age. Look closely at this nearly 9-foot-long piece of sandstone and you'll see the footprints of dinosaurs, flying reptiles, and mammals that lived and mingled in what is now Maryland more than 100 million years ago. Unearthed on the grounds of NASA's Goddard Space Flight Center in Greenbelt, Md., the slab--once soft mud--is providing insight into a time when North America teemed with these beasts. Because no prints overlap, scientists think it could be the most accurate record ever of prehistoric species crossing paths within a few days--or hours--of one another. As Ray Stanford, an amateur paleontologist who found the rock, told The Washington Post: "One could literally make a movie about everything going on in this slab."

Theropods

These sets of tracks were made by theropods--smaller cousins of...