An ancient bear with toothache
A North American fossil points to early ursine immigration and a sugar-rich diet. Jeff Glorfeld reports.
Winnie the Pooh’s fondness for honey is renowned, but author A.A. Milne never discussed his creation’s dental records. Now, however, researchers have identified remains of a 3.5-million-year-old bear, from a fossil-rich site in Canada's High Arctic, as being a close relative of the ancestor of modern bears, and which had a sweet tooth, demonstrated by cavities in the teeth.
In a report published this week in the journal Scientific Reports, the scientists identify the bear as Protarctos abstrusus, tracing its ancestry to extinct bears of similar age from East Asia. It was previously only known from a tooth found in Idaho.
The animal was slightly smaller than a modern black bear – average males of which weigh 160 kilograms, with exceptionally large ones tipping the scale at more than 272 – with a flatter head and a combination of primitive and advanced dental characteristics.
“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 paleontologist Xiaoming Wang, lead author of the study, from 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.”
Wang says this is the first and earliest documented occurrence of a high-calorie diet in basal bears and is likely related to fat storage in preparation for the harsh Arctic winters.
The research team, which included co-author Natalia Rybczynski from the Canadian Museum of Nature, studied bones from the skull, jaws and teeth, along with parts of the skeleton from two individuals.
The bones were discovered over a 20-year period by Rybczynski and colleagues in peat deposits at a location known as the Beaver Pond site, on Ellesmere Island, part of the Canadian Arctic archipelago. The site has also yielded fossilised plants indicating boreal-type wetland forest, plus remains of fish, beaver, small carnivores, deerlets, and three-toed horses.
The researchers conclude that the Ellesmere bear lived in a northern boreal-type forest habitat, where there would have been 24-hour darkness in winter, and about six months of ice and snow.
Rybczynski says it is a “significant find” because all other ancient fossil ursine bears, and even some modern bear species such as the sloth bear and sun bear, are associated with lower-latitude, milder habitats.
"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 characterised the ursine lineage from its beginning," she says.
Wang analysed characteristics of fossil bear remains from around the world to identify the Ellesmere remains as Protarctos, and to establish its evolutionary lineage in relation to other bears. Modern bears are wide-ranging, found from equatorial to polar regions. Their ancestors, mainly found in Eurasia, date to about five million years ago.
Fossil records of ursine bears are poor and their early evolution controversial, owing to the Ursidae family being divided into much-debated subfamilies. The new fossil represents one of the early immigrations from Asia to North America but it is probably not a direct ancestor to the modern American black bear.
Of further significance is that the teeth of both Protarctos individuals show signs of well-developed dental cavities, which were identified following CT scans by Stuart White, a retired professor from the University of California at Los Angeles School of Dentistry.
The cavities underline that these ancient bears consumed large amounts of sugary foods such as berries. Indeed, berry plants are found preserved in the same Ellesmere deposits as the bear remains.
“We know that modern bears consume sugary fruits in the fall to promote fat accumulation that allows for winter survival via hibernation,” says Rybczynski. “The dental cavities in Protarctos suggest that consumption of sugar-rich foods like berries, in preparation for winter hibernation, developed early in the evolution of bears as a survival strategy."