PORT HURON, Mich. (AP) — David Wentz was snorkeling 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,” said the 16-year-old Port Huron resident.

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 said 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, reached lengths of more than 60 feet.

By comparison, Great White sharks generally are about 20 feet long.

Gottfried suspects the tooth was probably carried and dropped by a human inhabitant of the region, either in recent historical times, or by earlier native people in the area.

“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.”