Thursday, March 25, 2010

Arctodus simus - America's Ice Age super-predator

When the first humans crossed the Bering Strait into North America they encountered a hunter's paradise, with mammoths, mastodons, giant sloths, and a variety of large ungulates for the taking. However, they also came face-to-face with some of the most fearsome predators of all time.

The dire wolf was larger and more heavily built than the present-day gray wolf. The large saber-toothed and scimitar cats had huge canines that could inflict horrendous wounds. The American "lion," which was larger than today's African lion, was related to the present-day puma.

However, the most terrifying predator of them all was Arctodus simus, known as the short-faced bear, which, at an estimated weight of 700 to 800 kilograms (1,543 to 1,763 pounds), was the largest carnivorous mammal that ever lived in North America.

Or was it?

In the 1960s, the late Finnish paleontologist Björn (Swedish for "bear") Kurtén, a leading expert on Ice Age mammals, especially bears, reconstructed Arctodus simus as an active predator. He emphasized the short, broad snout, powerful jaws, well-developed carnassials, and long limbs. A giant bear that could run down its prey would have been the ultimate nightmare for the first human settlers!

Later, a number of paleontologists cast doubts on Kurtén's interpretation. Some noted close similarities between Arctodus simus and its closest living relative, the primarily vegetarian South American spectacled bear, and argued that it also consumed a lot of plant matter.

Others suggested that Arctodus simus was an omnivore that frequently scavenged animal carcasses.

A new study by a team of researchers from the Universidad de Málaga in Spain has reassessed the rival claims concerning the way this extinct giant gots its dinner.

The first step taken by the Spanish team was to determine the body mass of Arctodus simus.

The weight of most mammals can be estimated from measurements of their limb bones. The researchers found a considerable range of weights, from about 300 kilograms (660 pounds) to almost one ton (2,200 pounds).

They also noted geographic variation, with the largest individuals coming from more northern locations. This pattern is still seen in populations of present-day brown bear, with particularly large animals (especially males) occurring in Alaska.

Second, the Spanish team looked at skull and limb proportions of Arctodus simus. The giant bear did not, in fact, have a particularly short snout and its skull proportions were appropriate for a bear of its size.

The researchers also noted that the most carnivorous living bear, the polar bear, has a relatively long snout. The tooth evidence provided no clear indication for either meat-eating or omnivorous habits.

Finally, while the forelegs may have been enlarged the hind legs in the extinct bear were not proportionately longer than in present-day bears. Arctodus simus was not a runner.

No longer short of snout and long of limb, Arctodus simus has been dethroned as America's Ice Age super-predator. However, studies of the carbon and nitrogen isotope ratios of its bones, commonly used to determine the dietary preferences of animals, still indicate the bear consumed some meat.

Presumably a one-ton bear could behave like the proverbial 800-pound gorilla--it could eat anything it wanted to!

Grizzlies consume a lot of vegetable matter yet, from time to time, will augment this diet by taking down an elk or the odd tourist. They will also chase wolves off their kills. The much larger extinct bear could easily have engaged in similar behaviors.

A mature adult Arctodus simus must have been a magnificent sight. Fortunately for Stephen Colbert and his fellow bear-haters, this giant vanished, along with the rest of America's remarkable Ice Age megafauna, some 11,000 years ago.

1 comment:

Anonymous said...

huge but i seen better