PORT HURON, Mich. (AP) -- David Wentz was snorkeling off Marysville Beach in the St. Clair River last August when what he thought was an odd-looking rock caught his eye.
"I didn't know what to think," the 16-year-old Port Huron resident said.
His father, Craig, said he knew right away what it was due to hours of watching the Discovery Channel.
"It's a shark tooth," Craig Wentz said. "It's petrified. It's rock."
Michigan State University paleontologist Michael Gottfried told the Times Herald of Port Huron that the 3-inch long tooth comes from an extinct species called Carcharodon megalodon, or the "megatooth" shark.
The megalodon, which went extinct 2 million years ago, was larger than any building in Port Huron, reaching lengths of more than 60 feet. By comparison, Great White sharks generally are about 20 feet long.
The megatooth shark ate about 1,500 pounds of food a day, mostly feeding on whales and other large marine creatures.
Gottfried doesn't think the tooth is from a shark that may have been in the Great Lakes region during two different prehistoric eras, dating back from a half-million years to 300 to 400 million years ago, when it was a "shallow marine environment" filled with sharks, whales and other aquatic life.
"I suspect that it was probably carried and dropped by a human inhabitant of the region, either in recent historical times, or perhaps by earlier native people in this area," he said.
"I can't say just how it came to be in the St. Clair River, but I can assure you that there aren't any sharks with 3-inch teeth living there now."