An amazing fossil find comes just after lunch
A slab of sandstone reveals an intriguing world that existed 100 million years ago
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, Maryland, not far north of the U.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 at Denver who studied the tracks.
Lockley and his colleagues described the findings in an article in the journal Scientific Reports. The slab offers unique insights into the behaviour of dinosaurs and early mammals — possibly some of the dinosaurs were looking to make a meal of the mammals.
All this might never have been discovered if an amateur dinosaur fossil hunter hadn’t gone to lunch with his wife not long before the construction of a new building obliterated the site.
Even back when dinosaurs ruled the world, the Washington, D.C., area was a swamp. Somehow, the right sequence of events allowed the traipsing of the animals across a muddy surface to be preserved in stone.
Millions of years later, the rock happened to be poking out to reveal its paleontological bounty.
At one end of the slab, there is a single footprint of a juvenile sauropod, a long-necked planteating dinosaur. At the other end is a print from a nodosaur — an armoured plant-eater as heavy as a small elephant.
Alongside are smaller footprints, a baby nodosaur following its parent.
There are also tracks of four theropods — relatives of the Tyrannosaurus rex that lived tens of millions of years later, but these were smaller, roughly the size of a large raven.
Elsewhere on the slab, pterosaurs walked around and even left indentations in the ground where they were pecking for something to eat.
The scientists even spotted at least one clump of what appears to be a coprolite, or fossilized feces. (They don’t know what pooped, but it may have been the sauropod.)
Most intriguing were the mammal tracks.
“The mammal track shape is very distinctive,” Lockley said. “Actually they look a little bit like very, very small pads.”
Footprints have been found before, but usually a single impression on a stray piece of rock.
Here, there are pairs of prints that show the left and right feet of the mammal in a sitting position.
Lockley said this was one of only two known sites where dozens of dinosaur-era mammal footprints had been found.
The discovery was made by serendipity, and almost lost forever.
Ray Stanford, an amateur paleontologist who has become an expert on dinosaur tracks, had just dropped off his wife, Sheila, who worked at Goddard, after the two went for lunch in 2012.
A few years earlier on the grounds of Goddard, Stanford had come across a loose rock with the footprint of a small three-toed theropod, and the brownish stone was the type of iron-rich sedimentary material that often preserves such prints.
As he was leaving the parking lot, he noticed rock of a similar colour sticking out of the grass on a nearby hill.
Stanford stopped the car and went to take a look, and spotted a prominent dinosaur footprint. “Lo and behold,” he said. “It’s a perfect large nodosaur. This one was beautiful. I was in ecstasy as a tracker.” But there was a problem. Goddard was about to rip up the parking lot and the hill and put a $31 million office building there. Officials called Compton J. Tucker, a Goddard scientist who has participated in geophysical surveys to find buried ruins at archeological sites. Tucker recalled that as he listened, he thought, “This sounds kind of strange but it sounds interesting.”
Additional examination revealed the baby nodosaur’s footsteps and the sauropod print at the other end of the slab.
Before construction of the building started, Tucker used ground-penetrating radar to search for other promising pieces of sandstone. Then an army of volunteers dug up those areas. But none of the other pieces turned out to be as interesting as the ones Stanford found.