4-foot clam fossil discovered in Utah

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PRICE — Both men knew what they were looking for when they headed out early last year to explore the edge of the Book Cliffs in Emery County.

"We were out looking for mosasaurs and plesiosaurs, big marine lizards that are common in the Cretaceous sediments farther east, but are very rare in Utah," Lloyd Logan, director of education and exhibits at Utah State University-Eastern' Prehistoric Museum, said Thursday.

But what Logan and museum director Kenneth Carpenter found near Green River turned their small expedition into one big clam dig.

"As soon as we crossed the railroad tracks and started walking around, we immediately began to find fragments of the clams," Carpenter said. "Within 30 minutes, we had found over a dozen that were pretty badly weathered and eroded out. They were too damaged to collect."

The men made note of the location and then made a plan.

"We decided to come back and look for one that was just beginning to erode," Carpenter said.

What they would later unearth from the crumbling Mancos shale was a first-of-its-kind discovery in Utah.

"This one here is 4 foot across, and there's nothing like it living today," Carpenter said, gesturing to the large fossil clam now on display in the museum.

The giant clams lived on the sandy bottom of the Mancos Sea, which once cut through North America from the Arctic Ocean to the Gulf of Mexico. The clam Lloyd and Carpenter found is twice the size of the largest living clam species.

Carpenter, who stands five feet tall, helped unearth a clam that's almost as big as he is from a prehistoric seabed that once split North America in two.

"This clam lived in the age of the dinosaurs," Carpenter said. "It lived some 20 million years before Tyrannosaurus rex, but long after stegosaurus and allosaurus."

The clams weren't alone on the seafloor though. Their flat, broad shells served as a host for other marine life, as evidenced by the fossilized oysters that still remain fixed in place.

"Oysters need some kind of structure to attach themselves to," Carpenter said. "Since there were no rocks on the seafloor, no coral reefs or anything, all they had were these clams."

And while giant prehistoric clams have already been found in Colorado and Kansas, Logan and Carpenter's is the most complete one ever discovered in Utah. It also sets a new western boundary for the species' known range.

"This is a first for the state, so I think it's something Utah should be proud of," Carpenter said.

"When you have your 'a-ha moment,' and you realize this has not been seen before — or at least no one had ever reported it — you get kind of a rush," he added.

Logan agreed.

"It is a rush. I can't say I've done drugs, but it's gotta be better than drugs," he said.

Both men say they plan to return to the Book Cliffs soon to continue their search for other prehistoric marine life. They'll also be looking for an even larger clam.

"There's probably a clam down there that I could make into a bed," said Carpenter, who is 5 feet tall.

"There's undoubtedly some clams down there that are 6 foot, maybe even 7 foot," he said. "There's a lot about the seafloor that we don't understand, and now that we've found these giant clams, it's given us a picture that we can expand on."


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Geoff Liesik


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