A variety of big herbivores additionally lived in the region at the time, providing plenty of dinner options for the enormous bear.
"A. angustidens probably had an omnivorous diet composed of a great variety of components, but with a predominance of animal remains," said Soibelzon. "Among them, probably the bones and flesh of large mammals were very important in its diet."
The particular male bear individual that the scientists studied reached old age despite sustaining serious injuries during its life. The fossilized remains still retain signs of those injuries.
The researchers aren't certain what caused the physical damage, but Soibelzon said that "certainly male-to-male fighting would be a possibility."
"Other possibilities include hunting megafauna, like giant ground sloths," he added, "and disputes with other carnivores, such as a saber-toothed cat, over a carcass."
Schubert said the bear was part of a group of bears known as the tremarctines that has only one living representative: the spectacled bear. This modern bear is a relatively small species, reflecting selection pressures that have occurred over the years. During the Pleistocene, however, huge bears lived in both South America and North America. Europe was also home to a gigantic cave bear.