In 2004, geologist Pannipa Tian noticed something unusually cream-colored standing out from the dark veins of coal marbled through Bang Mark Pit, a coal mine in southern Thailand’s Krabi province. Initially, Tian “thought it was a bone,” as she told Agence France-Presse last Thursday. It was exactly the kind of find that the Thai–French Paleontological Expedition on Fossil Mammals in Thailand hoped to rescue before day-to-day activity on site damaged it for good. But it turned out this prehistoric fossil wasn’t a bone at all.

“I showed it to my supervisor, who told me it was a giant rat’s tooth,” Tian said.

Now researchers from Thailand, France, and Canada have determined that this tooth—a roughly 2-inch (5-centimeter) incisor fragment—and a large dark molar discovered that same day at the mine belong to a previously unknown species of giant rodent.…