Telling footprints

Fossilized tracks found in Maryland streambeds prove dinosaurs, young and old, walked Eastern Seaboard

August 17, 2007|By Frank D. Roylance | Frank D. Roylance,Sun reporter

Hundreds of dinosaur footprints, in rocks plucked from Maryland streambeds by an amateur paleontologist, are being described in a scientific journal as among the most significant of their age in North America since the 1930s.

The tracks reveal the presence more than 112 million years ago of at least 14 different kinds of animals, from carnivorous and plant-eating dinosaurs to birds, lizards and mammals. That's twice the diversity found anywhere else in rocks from the same period, the Early Cretaceous.

That makes Maryland's urban corridor one of the richest sites for Cretaceous dinosaur track fossils in the world, ranked among such places as Texas, Colorado, New Mexico and Utah, as well as sites in Japan, Korea, Spain and China.

What's more, the finds include a high proportion of very small dinosaur prints, suggesting the place was a dinosaur rookery - a rarity in such deposits, according to the paper in the July issue of the journal Ichnos.

"There aren't that many places where you get this many species, and from very young animals and adults on the same spot," said Matthew T. Carrano, curator of dinosaurs at the Smithsonian Institution's National Museum of Natural History in Washington. "It's extremely important, even on a global scale."

Ray Stanford, the 69-year-old College Park amateur whose home he filled with rocks until the floors had to be reinforced, wrote the paper with Martin G. Lockley, professor of geology at the University of Colorado in Denver, and Rob Weems, a geologist with the U.S. Geological Survey.

Until his collaboration with Lockley and Weems, Stanford said, he hadn't realized the importance of his finds. "That just floored me."

He found the fossilized tracks in rocks from the Patuxent Formation, which contains the oldest rocks exposed along the Atlantic coastal plain. Like the bottom slab of a tilted layer cake, its outcrops reach the surface in a narrow band that parallels Interstate 95, from the Maryland-Delaware line to Fredericksburg, Va.

"No other geologist ever recognized the stuff there," said Lockley, who is also director of his university's Dinosaur Tracks Museum said. "They had written off the Cretaceous in that part of the world as not having the potential to find tracks."

Dinosaur tracks typically come in sets of two or three, or in a trackway that helps scientists understand how an individual species moved.

In Maryland's Patuxent Formation, the Smithsonian's Carrano said, all the tracks were laid down over perhaps a million years. "We can say this was a community of animals, and you start to understand more about the paleoecology."

Although scientists might have predicted which animals lived here, few fossil bones or teeth have been found. The deposit just didn't preserve many.

"Now, you have proof," Lockley said. "This has just completely changed what we know about the Lower Cretaceous of the eastern seaboard."

Although papers on several of Stanford's finds have been published over the years, this article is the first formal description of the collection in a peer-reviewed journal - in effect, its introduction into the scientific literature.

Ichnos is a British-based international journal for research into plant and animal "traces" - the fossil signs that animals left behind, such as burrows, trails, borings and footprints, but not their bodily remains.

Normally, scientists would now compare the finds to others. "But there isn't anything to compare to," Carrano said. "This is a totally new piece of information."

With Stanford's discoveries, Maryland has gone "from `nowhere' to being in the top 10 [sites in Cretaceous paleontology], especially if you take into consideration the uniqueness of the fauna and the small size and high diversity," Martin Lockley said.

"I knew it was very significant," Stanford said, "but I didn't realize the significance in that context. I'm grateful to Martin for enlightening me. I'm just thrilled with it."

The collection includes more than 300 specimens. Lockley selected about a third of those for preliminary description.

The prints were pressed into iron-rich silt, sand and clay laid down almost 50 million years before the dinosaurs disappeared.

The land at that time was a swampy region of river deltas, sluggish flood plains and oxbow lakes, scientists say. The sediments were washing down from mountains to the west, flowing toward the sea, a few dozen miles to the east.

The muddy footprints quickly solidified into rock, made harder by its high iron content. The rock layer was later broken apart by further stream erosion, and those fragments were buried by subsequent deposits. They are only now washing out of the softer sediments.

Since 1994, Stanford has been picking them up from the beds of streams that cut through the formation in Prince George's and Baltimore counties. He won't disclose exactly where.

Educating himself as he went along, Stanford amassed a menagerie of tracks that astonished Lockley when he first saw them in Stanford's house in 1999.

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