Cave bears, the close cousin of the brown bear, roamed vast swaths of present-day Russia across to the United Kingdom and down to Spain for hundreds of thousands of years until they went extinct 25,000 years ago. A large beast at roughly 12 feet long and 5 feet tall at the shoulder, the cave bear—so named because they hibernated in caves, though they didn't live in them—left behind a trove of bones and teeth for scientists to study, so one group decided to investigate their teeth for clues to their mysterious extinction, reports Phys.org. What they learned is that the bears, unlike their omnivorous relatives today, were "strict" vegans, eschewing fish, small mammals, and insects, they report in the Journal of Quaternary Science.
"Similar to today's giant panda, the cave bears were therefore extremely inflexible in regard to their food," one researcher writes. "We assume that this unbalanced diet, in combination with the reduced supply of plants during the last ice age, ultimately led to the cave bear's extinction." Of course, this is just an assumption, and the scientists say they're now working on studying more teeth and bones to learn more. So far the team has been able to use a portable scanner popular with dentists to create 3D scans of molars from the lower jaws of cave bears and other bears that today roam the Northern Hemisphere, such as black Asiatic and polar bears, reports Science magazine. The team also notes a head-scratcher: Two cave bear cubs had collagen suggestive of a vegan diet, though they were nursing. (This man survived being pulled into a cave by a bear.)