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Fossilized footprints trace pre-historic sea scorpion

New on view at the Carnegie Museum of Natural History are the fossilized footprints of a 7-foot sea scorpion -- an eurypterid -- from prehistoric Elk County.

"Think of a giant lobster. It's very closely related. ... It had a scorpion-type tail," says geologist David K. Brezinsky, associate curator adjunct of invertebrate paleontology at the museum.

Scientists don't know exactly where the predator lived -- perhaps in a river or brackish bay -- long before dinosaurs roamed the Earth.

"All we have is the impression of its movement through sediment," says Albert Kollar, another geologist at the museum. "We don't know what the shape of these feet are. We don't know what this animal looked like."

A prehistoric sea scorpion -- also related to the horseshoe crab -- made the footprints about 350 million years ago during the Mississippian Period of the Paleozoic era. The creature had six pairs of legs, including one pair of large, claw-like appendages, plus a large tail.

People can view the creature's footmarks on what looks like a nondescript slab of brown-gray sandstone in the Benedum Hall of Geology. The overlooked specimen was taken out of storage after Yale University paleontologist Dolph Seilacher ordered a cast of the specimen for a proposed traveling exhibit.

Impressions made by the ancient arthropod's jointed feet are all you see on the world's largest "eurypterid trackway," as a plaque describes the specimen.

Eurypterids were prehistoric invertebrates that lived in water and preyed on other invertebrates, perhaps snails, clams and trilobites.

"Trackway" or "trace" fossils reveal animals' tracks, footprints and burrows, rather than animals' body forms.

A faint groove -- probably made by the animal's scorpion-style tail -- bisects the prized rock and indicates that the animal probably moved between water and land.

Typical eurypterids measured about 12 inches, compared to the nearly 8-foot eurypterid that left its footprints in this chunk of sandstone.

"They were probably the biggest predators of the time, and this was probably the largest predator on earth," Brezinsky says. "It's probably the largest eurypterid ever discovered."

An artist's rendering of the creature reminds volunteer museum docent Preston Ader, 14, of Charleroi of a large shrimp.

"Imagine eating that for dinner," Preston says. "I'm extremely impressed by this."

Late Carnegie museum employee James Kosinsky and his brother, Michael, accidentally spotted the trace fossil near the Clarion River on a 1948 hunting trip.

In 1983, British scientists Derek E.G. Briggs and W.D. Ian Rolfe described and named the creature Palmichnium kosinskiorum .

Briggs and Rolfe first learned about the ancient animal after Princeton University paleontologist Don Baird, a Pittsburgher, saw the animal's trace fossil at Carnegie Museum of Natural History in the early 1980s.

Kollar and Brezinski plan to soon revisit the site where the Kosinsky brothers found the trace fossil.

"This fossil warrants new research as to the environment in which those sediments were discovered," Kollar says, "which will shed light on how this animal lived, and where this animal lived," says Kollar.

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