GREENBELT, Md. — Some 110 million years ago, in the swamp that would become the Washington suburbs, a hulking, armored nodosaur trudged along a riverbank, leaving a telltale print in the mud. Its offspring scrambled after it, slipping in the parent’s print. Other dinosaurs crowded the setting: A long-necked sauropod squelched through the muck, while several theropods — smaller cousins of the fearsome T-rex — stalked the landscape. Perhaps they were in pursuit of the small, rodent-like creatures hopping about.

Within days, a flood covered the many footprints with rock, preserving them. Millennia passed. An asteroid struck, the continents shifted, sea levels fell, mammals rose, humans climbed down from trees and launched toward the stars. Finally, on a summer day in 2012, a self-taught fossil hunter named Ray Stanford noticed the unmistakable shape of the nodosaur’s track as he drove out of a parking lot at what is now NASA’s Goddard Space Flight Center in Greenbelt.

“I like to call it the Rosetta Stone,” said Martin Lockley, a dinosaur track expert at the University of Colorado Denver who participated in the research. The evidence on that slab surface preserves animals as they lived rather than as they died — revealing the ecology of their age in exquisite detail, he said.

Source: Kaplan, Sarah, Spectacular dinosaur stomping grounds discovered just outside D.C., The Washington Post, January 31, 2018, https://www.washingtonpost.com/news/speaking-of-science/wp/2018/01/31/spectacular-dinosaur-stomping-grounds-discovered-just-outside-d-c/?utm_term=.4b57a0cfdbb6