Bears of the Pleistocene

[brotherbear]

Ice Age Mammals of North America by Ian M. Lange.

Short-faced bears - genus Arctodus.

The giant and lesser short-faced bears and the spectacled bear of South America probably descended from an earlier tremarctine, Plionarctos, that lived between 5 million and 10 million years ago in Texas. Both short-faced bears were widespread in North America by 800,000 years ago.

The giant ( Arctodus simus ) and lesser ( Arctodus pristinus ) short-faced bears resembled each other. Their snouts appear short relative to the size of their heads - thus, the name 'short-faced' bear. The width of the giant's skull was 80% that of the skull's length. With short faces and wide muzzles, the skulls of these two species resembles that of a big cat.

Both bears were less pigeon-toed than living bears and so walked a straight path rather than waddling from side to side. This toe-foot structure probably allowed the short-faced bears to run faster than brown or black bears. Most males were on average 15% larger than female bears. Studies of bones of both species show that some of these bears suffered from diseases similar to tuberculosis and syphilis.

The giant and lesser short-faced bears differ from each other in several important ways. The giant short-faced bear was not only at least several hundred pounds larger, but it also had longer legs, a shorter snout, and bigger, broader, and more crowded teeth well adapted to eating meat. The tooth structure of the lesser short-faced bear supported a more omnivorous diet than did that of its bigger cousin.

The lesser short-faced bear lived in the eastern United States and south into Mexico, preferring the wetter, forested regions. These magnificent animals lived until at least about 20,000 years ago.

The giant short-faced bear evidently preferred the more open, drier, grassy country west of the Mississippi River. Remains have been found from Alaska and Yukon south into Mexico, and from Pennsylvania west to California. Specimens of these animals found in the La Brea tar pits in southern California and elsewhere north into the Arctic show that the more northerly bears were larger than their cousins to the south. Cave remains are not uncommon, so both male and female bears may have inhabited caves for part of the year where they were available.

The giant short-faced bear, while long legged, was relatively short bodied for its leg length when compared with living bears. It also was not as heavily built as brown or grizzly bears. Even so, giant short-faced bears reached enormous size. At 5.5 feet tall and almost 10 feet long, the giant short-faced bear would dwarf the modern grizzly, which measures up to 4 feet tall and 9 feet long. When standing on their hind feet, the top of their headwas more than 11 feet high. Male giant short-faced bears probably weighed more than 2,000 pounds in the fall prior to hibernation. Compare this with a large grizzly bear, which before hibernation weighs about 1,700 pounds.

The giant short-faced bear has been traced back to Irvingtonian Land Mammal Age. It may have come north from South America and coexisted with brown and grizzly bears. The youngest remaims of these giant bears date at 12,650, plus or minus 350 years, before present. At least thirty specimens have been recovered from the La Brea tar pits in California and one from the Columbian mammal burial pit at Hot Springs, South Dakota. Other important fossil localities are in Texas, Montana, Utah, and Wyoming.

What did the giant short-faced bear - the largest and most powerful of the Pleistocene bruins - eat? Whatever it was, they needed a lot. Paul Matheus, director of the Alaska Quaternary Center in Fairbanks, is convinced that these steppe-loving animals - with their very powerful jaws and large teeth capable of ripping, crushing, and gnawing - ate only meat. His proof comes from their bones. The ratio of two isotopes of nitrogen 15 and nitrogen 14, in bones can help researchers distinguish between carnivores, herbivores, and omnivores. Herbivore bones contain a low ratio whereas carnivore bones have a high ratio. Matheus found that the bones of giant short-faced bears have a high ratio of nitrogen15 to nitrogen 14, supporting the contention that the animals were highly carnivorous.

Matheus's research also leads him to believe that the bone structure of this animal was not strong enough for it to bring down really large animals without getting hurt. Smaller animals such as horses, however, could evade the fast but less maneuverable bears. Matheus, therefore, thinks these animals were scavengers and that this lifestyle probably contributed strongly to their extinction. Once the other predators, such as American lions and scimitar cats, and their large prey were gone, there was not enough carrion left for the giant short-faced bear. Reply