Black bear
Modern day American black bears are still fond of eating fruit Rick Wilking/ Reuters

Ancient bears that roamed the North American continent around 3.5 million years ago ate so much fruit that they had cavities in their teeth. This is the first recorded instance of bears bearing oral infections and the first evidence that researchers have found where animals prepare for harsh winters by eating high calorie diets.

This study was done by the Canadian Museum of Nature in collaboration with the Natural History Museum of Los Angeles County, notes a report by The bones and fossils found in the Canadian Arctic show how closely these ancient bears were related to their modern-day cousins.

Called Protarctos abstrusus, these ancient animals were previously known only from one tooth that was found in Idaho. After 20 years of research and bone collecting, the team has concluded that they were only slightly smaller than a modern day black bear. Being transitional in nature, they had flatter heads and possessed a mix of primitive and advanced dental characters.

"This is evidence of the most northerly record for primitive bears, and provides an idea of what the ancestor of modern bears may have looked like," says Dr. Xiaoming Wang, lead author of the study and Head of Vertebrate Paleontology at the Natural History Museum of Los Angeles County.

"Just as interesting is the presence of dental caries, showing that oral infections have a long evolutionary history in the animals, which can tell us about their sugary diet, presumably from berries. This is the first and earliest documented occurrence of high-calorie diet in basal bears, likely related to fat storage in preparation for the harsh Arctic winters," explained Wang.

Researchers also studied the bones, skull, teeth, and jaws from different individual bears. The site where bones were recovered from shows evidence of it being a forest habitat and it was a region that likely had 24-hour periods of darkness and harsh winters with six months of ice and snow.

"It is a significant find, in part because all other ancient fossil ursine bears, and even some modern bear species like the sloth bear and sun bear, are associated with lower-latitude, milder habitats," says co-author Dr. Natalia Rybczynski.

"So, the Ellesmere bear is important because it suggests that the capacity to exploit the harshest, most northern forests on the planet is not an innovation of modern grizzlies and black bears, but may have characterized the ursine lineage from its beginning," she added.

Fossils from around the world were analysed to identify the ancient bears, and evolutionary lineage in relation to other bears was also established in the study. According to the research, modern day bears range from the arctic to equatorial regions and that bears have common ancestors that date to nearly five million years back.

While the fossils found might not be of an animal that is a direct ancestor to the American black bear, researchers say that it does represent one of the early immigrants from Asia to Northern America.