MUNICH.- For most mammals, teeth grow according to a fairly reliable plan. Follow the pattern, and you can often tell what an animal eats simply by looking at the size and order of its molars. Bears, it turns out, are the great exception.

Researchers from the Bavarian State Natural Science Collections (SNSB) have uncovered why modern bears have such unusual teeth—and the answer reaches back millions of years into their evolutionary past. Their findings, published in the scientific journal Boreas, reveal that two key moments in bear evolution permanently reshaped how their molars develop.

In many mammals, tooth growth follows what scientists call the Inhibitory Cascade Model. In simple terms, the first molar in the lower jaw sets the tone for the teeth that follow. Carnivores tend to have a large first molar and smaller ones behind it, while herbivores show the opposite pattern. The balance is closely tied to diet and to molecular signals that either promote or inhibit growth.

Modern bears don’t play by these rules. Across almost all living species—whether meat-eaters, plant-eaters, or omnivores—the second molar is the largest. This oddity puzzled scientists for decades.

To trace its origin, zoologist PD Dr. Anneke van Heteren and her doctoral researcher Stefanie Luft examined jaws from both fossil and living bears, comparing them with the expected model. Their material spanned deep time: the oldest jaw they studied dates back more than 13 million years, to the Miocene.

The first major shift appeared around 3.6 million years ago, in Ursus minimus, thought to be the common ancestor of most modern bears. At this point, the second molar began growing disproportionately large. A second break occurred much later, between roughly 1.25 and 0.7 million years ago, in the early cave bear Ursus deningeri, when the third molar exceeded its expected size.

“These changes suggest that the biological signals controlling tooth growth were altered at specific moments in bear evolution,” van Heteren explains. “Those shifts likely reflect how bears adapted their diets over time.”

As climates changed, so did landscapes—and food sources. The first dental shift coincides with the transition from subtropical forests to more open shrublands and steppes during the Pliocene. The second occurred as grasslands expanded and temperatures cooled during the Pleistocene. Bears were evolving from strict carnivores toward omnivory and, in some cases, largely plant-based diets—but without conforming to the standard dental blueprint seen in other mammals.

Today, bears still embody this evolutionary flexibility. From the meat-eating polar bear to the bamboo-specialist giant panda, their diets vary widely, yet their teeth retain the same unusual pattern. The study shows that this shared trait is not a quirk of modern life, but the legacy of ancient evolutionary turning points—moments when bear teeth, quite literally, danced out of line.