In one of the most productive periods of dinosaur fossil-hunting in Maryland since the 1880s, large dinosaur bones are coming to light, as keen-eyed amateurs join scientists in searching for evidence that the prehistoric creatures once roamed the area.
The latest major find occurred May 19 at a well-known fossil site ina clay quarry near Laurel. Greenbelt resident Arnold Norden spotted a huge, 6-foot-long thigh bone that had been partially exposed and damaged by grading equipment.
"It was incredibly exciting, just to know this bone was being seen for the first time in 110 million years," said Mr. Norden, an experienced fossil collector who works as an aquatic ecologist with the Maryland Department of Natural Resources.
After carefully encasing the fragile bone in plaster for safe removal, experts from the Smithsonian's National Museum of Natural History identified it as a femur from an adult sauropod, the general classification for plant-eating dinosaurs with long, slender necks and long tails.
They narrowed it down to the family brachiosauridae and, with less certainty, the species Astrodon. By extrapolating from the femur's size, they estimate the animal weighed 15 to 20 tons and measured 36 to 37 feet high.
"That's a big dinosaur, and this is the biggest dinosaur bone that's ever turned up in the Northeast," said Nicholas Hotton, a curator of paleobiology at the Smithsonian. He said the bone is presently being stabilized in the laboratory by impregnating it with plastic.
Fossils of Astrodon, mostly teeth and bone fragments, are the most abundant dinosaur remains in Maryland, and scientist Peter Kranz -- author of the 1989 pamphlet "Dinosaurs in Maryland" -- is lobbying to have it named the state dinosaur.
It's one of at least a half-dozen species thought to have lived in this area from about 228 million to 70 million years ago. For much of that time, Maryland was a lush tropical plain cut by rivers and undergoing stresses from volcanic and seismic activity.
The surviving remains -- from the Early Cretaceous period 130 million to 95 million years ago -- now lie in a narrow strip of coastal plain running diagonally from Washington through Cecil County along the Route 1 corridor, a layer of gray clay called the Arundel formation.
And hundreds of fossils began showing up during mining operations to extract iron deposits from that clay layer in the 1800s and early 20th century. Those sites and others in Maryland and Washington have yielded the only Early Cretaceous dinosaur material on the East Coast.
There have been numerous small finds since then, but the iron mines went silent before World War I, and development has paved over the majority of potential fossil sites between Baltimore and Washington.
Unlike the drier West -- where erosion has exposed big bone beds with intact dinosaur skulls and skeletons -- Maryland has lush vegetation that quickly reclaims the land, and fossils are now found only through excavations in the clay layer or in rare exposed outcrops.
"In this area, the finds are few and far between. The bones are so scattered," Mr. Norden said. "Professionals can't spend their time looking because it's just incredibly rare to make a significant discovery. The legwork has to be done by amateurs."
A 30-year veteran of fossil-hunting throughout Maryland, he said the field trip to the Laurel quarry with his children, Heather, 10, and John, 7, just happened to be his "first try at dinosaurs."
The Arundel clay is easy to spot by its gray color, unlike more common red or yellow or brown layers. Other clues are tiny
fossilized pine cones and pieces of ancient cypress wood that resemble charcoal.
But it was only after several fruitless hours of intently searching .. the ground, after the kids "had given up and were cooling off down in the mud where the tadpoles are," that Mr. Norden found the bone fragments that led him to the partially exposed femur.
"They're excavating back into a hill at that point, and this probably would have been 20 feet down from the surface," he said. "If they had scraped 6 inches deeper, it would have been destroyed; 4 inches higher, and it would still be undiscovered."
In August 1989, part of another adult Astrodon femur was found by mineral collector Robert Eberle at a site in southeast Baltimore County between Interstate 95 and the Baltimore-Washington Parkway.
And, together, the finds have shot down an earlier theory that Astrodon was a small dinosaur. "For reasons we still don't know," said Mr. Hotton, "the fossils found here have largely been from juvenile dinosaurs, and it was mistakenly thought to be adult material."
"This thigh bone tells us how big Astrodon was when he grew up," he said, "and it clearly demonstrates that dinosaurs of the East were just as big as dinosaurs out West."
Mr. Hotton is philosophical about continued quarrying at Maryland's best dinosaur-fossil site. "I guess it would bother me if I let it," he said. "But paleontologists don't dig, they walk. We count on Mother Nature and excavations like this to work the miracles."
The Smithsonian has no plans to methodically search for more bones at the site or to display the thigh bone at the Museum of Natural History, he said. It will be added to the collection of Maryland dinosaur fossils for study by scholars and serious amateurs.