Ancient cave bears, which roamed from the United Kingdom to Russia for hundreds of thousands of years, made a strong impression on Stone Age artists, who included them in a 30,000-year-old gallery of animals lining the walls of Chauvet cave in modern France. But the cave bear mysteriously went extinct about 24,000 years ago—and new research is offering some tantalizing clues as to why. Climate change, specialized diets, and unique hibernation strategies are among the many hypotheses for why the cave bears died off, whereas their close cousin—the brown bear—survives to this day. To narrow the list of possibilities, one group of scientists looked to a well-known marker of diet: teeth. Once they come in, teeth don’t grow and they don’t shrink, except in response to wear and tear. Using a portable scanner popular with dentists, the scientists created 3D scans of molars from the lower jaws of cave bears and other Northern Hemisphere bears, including polar bears and black Asiatic bears. They then calculated the “complexity” of the different molar crowns by looking at their arrangement of ridges and cross-ridges. The cave bears had the most complex molars out of all the bears, suggesting that they may have had a highly specialized vegetarian diet, the researchers reported in Washington, D.C., today at the International Conference of Vertebrate Morphology. This could have contributed to their vulnerability to extinction. But an even more tantalizing clue lies in the the shape of the cave bears’ second molars. From bear to bear they were highly variable, suggesting the animal was under a lot of environmental stress.