A male South American giant short-faced bear has just broken the record for world's largest bear, according to a paper in this month's Journal of Paleontology.
Standing 11 feet tall and weighing in at about 3,500 pounds, the bear, which lived in Argentina during the Pleistocene Ice Age, would have towered over the world's largest individual bear from an existing species. That distinction belongs to a male polar bear that weighed in at 2,200 pounds.
Huge body size benefited the South American giant short-faced bear (Arctotherium angustidens) during the species' existence from a half-million to 2 million years ago.
"During its time, this bear was the largest and most powerful land predator in the world, so we think it lived free of fear of being eaten," co-author Leopoldo Soibelzon told Discovery News.
Soibelzon, a researcher in the Vertebrate Paleontology Division at the La Plata Museum, and colleague Blaine Schubert of East Tennessee State University made the determinations after analyzing the bear's fossilized remains.
The fossils were unearthed during a La Plata City construction project. They were donated in 1935 to the museum there, where the bones have been since.
Extensive prior work conducted by the authors looked at other extinct and living bear species. The research found that the most reliable predictor of body size in bears is based on seven particular bone measurements. Soibelzon and Schubert calculated the giant bear's size using these measurements of leg bones, along with equations for estimating body mass.
The scientists think the bear evolved to become so huge because of the absence of other large carnivores in its habitat. The saber-toothed cat was also high up on the Argentina food chain at the time, but it still was much smaller than the South American giant short-faced bear.
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 that the scientists studied reached old age despite sustaining serious injuries during its life. The fossilized remains 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.
Eduardo Tonni, head of the Vertebrate Paleontology Division at the Museo de La Plata, told Discovery News he agrees with the new findings since the conclusions made by the authors "are well sustained by the fossil record and current knowledge." Tonni said the two researchers have been studying important fossil collections for prehistoric South American, North American and European mammals over the last 14 years.
Tonni added that the researchers "analyzed and compared, for the first time, the evolutionary trends of fossil and living bears."