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Ancient Utah seabed yields sunken surprise: giant clam shells

Director Kenneth Carpenter examines the giant clam shell that has just gone on display at the USU Eastern Prehistoric Museum.
John Bird did some of his preparatory work in public during the museum's Family Day in May.
Fossil preparation takes many hours of delicate work.

At 4,000 feet above sea level near Green River, two USU Eastern Prehistoric Museum staffers were searching for marine reptiles last summer and stumbled upon prehistoric giant clams strewn throughout the landscape.

Dr. Kenneth Carpenter, paleontologist and director of the museum, had joined colleague Lloyd Logan, director of education and exhibits, for a hike searching for signs of ancient life.

The two were walking across the hot, dry and desolate landscape when they spotted what looked like giant clam fossils.

Carpenter said, "Stumbling upon those giant three- and four-foot clams was a real surprise. In places, they were so thick we could literally walk from clam to clam. These clams lived 85 million years ago, during the Age of Dinosaurs, when this part of Utah was under the ocean." A first for the area

The clams were found eroding out of the Mancos Shale, the soft, gray rock that lies at the foot of the Book Cliffs. Although smaller clams and Nautilus-like ammonites have been found in the Mancos Shale in the area, giant clams had never been reported before.

According to Carpenter, there are no reports of giant clams ever being found in Utah, and only a handful of giant clams are on display in museums throughout the country.

These giant clams look like large dinner-plates, hence the scientific name Platyceramus means "flat clam." Today, giant clams are nowhere near the giant four-foot-diameter clams in size. The modern pip-squeaks are only two feet or so across and are native to the shallow coral reefs of the South Pacific and Indian oceans.

They have also been found off the shores of the Philippines and in the South China Sea. They have never been found in Utah, let alone near Green River. Environment favored big, flat bodies

The areas where the clams were found was once a flat, muddy seafloor. That is a key to understanding why they grew to such monsters.

The large clams could spread their weight over a large area to keep from sinking into the seafloor. "These clams became the home to oysters that grew over the shells, as well as the home to small fish that lived within the shells," Carpenter said. "Numerous fish bones were found within the shells during the excavations."

After finding the clams, the two secured the site and returned to it later with museum personnel and volunteers to retrieve them. Because the clam shells are so thin, a wooden frame was built around the shell, and then Plaster of Paris was poured directly on the shell. When dried, the plaster-covered shell was flipped over and taken to the museum, Carpenter said.

John Bird, paleontology technician for the museum, worked with Carpenter for several months to prepare the clams for display at the museum. While Carpenter and Bird were working on the clams, Logan was creating and designing an exhibit to house the fossils for the public to view.

The giant clam is 44 inches by 48 inches, but in life might have weighed 50 pounds.

Their average life span might have been 100 years or more.

Located in the Hall of Paleontology, the giant clam display is open and ready for the public to view at the museum located at 100 North and 100 East in Price. The hours are Monday-Saturday from 9 a.m. to 5 p.m. (general admission rates apply)

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