Arctodus Simus by Moondawg

Arctodus Simus by Moondawg 2008

Arctodus, is also known as the Short-Faced Bear. One species, the Giant Short-Faced Bear (Arctodus simus), is the largest bear that ever lived based on fossil finds. It lived in prehistoric North America from about 800,000 to 12,500 years ago.

Short faced bear (Genus: Arctodus) is an extinct animal of prehistoric bears of the subfamily Tremarctinae. Arctodus simus, along with many other large mammals, became extinct during the Pleistocene epoch. It was preceded in time by A. pristinus, an evolutionary cousin or even ancestor of A. simus, proportionally shorter of leg and longer of muzzle

The short-faced bears belonged to a group of bears known as the tremarctine bears or running bears, which are endemic to the New World. The earliest member of the Tremarctinae was Plionarctos, which lived in Texas during the Pliocene Epoch, (2-5 mya). This genus is considered ancestral to Arctodus, as well as to the modern spectacled bear, Tremarctos ornatus. Although the early history of Arctodus simus is poorly known, it evidently became widespread in North America by the Kansan age (about 800 kya).

Arctodus simus stood as high as two meters (seven feet) at the shoulder on all four legs. When standing bipedally, the animal was over 3.3 m (10 feet) in total height, with a possible reach of almost 4.2 m (14 feet). It is estimated to have weighed 600-860 kg (1300-1900 pounds), around the same weight of its contemporary (or slightly larger) the grizzly bear. The largest specimens were found in Alaska and the Yukon Territory. Males were 20% bigger than females.[3] It was the largest land predator during the Ice Age in North America. The skull was unusual due to its lack of a well-defined forehead and the presence of a short broad muzzle, resembling that of Panthera rather than that of any modern bears. The muscles which passed between the broad cheek bones to power the lower jaws were extremely well-developed and are thought to be adapted for bone crushing in order to obtain the rich marrow. An Arctodus lower jaw can be distinguished from those of the genus Ursus by the slanting ridge dividing muscle attachment areas. Rather than having a waddling gait like modern bear species, Arctodus had toes extending straight forward, presumably being able to move with greater ease. In addition, unlike Ursus, Arctodus had a passage on the lower inside portion of the humerus for a slip of muscle (entepicondylar foramen).

Arctodus had a very short, broad muzzle, the skull having an olfactory area twice as large as that of a grizzly, and this, along with its great height, likely allowed the bear to identify a carcass from much greater distances. The jaw bone was massively foreshortened as in a feline, allowing Arctodus to eat even bone and marrow.

There are currently two recognized subspecies; the large specimens of Alaska, Yukon, Nebraska, California (Irvington) and perhaps Utah are called A. s. yukonensis, while the smaller specimens of Rancho La Brea are A. s. simus.

It was distinguished from its cousin (and possible ancestor) Arctodus pristinus by its bigger, broader, more crowded teeth, its shorter face, and its relatively longer legs.

Analysis of A. simus bones show it occasionally suffered from diseases such as osteomyelitis, as well as tuberculosis-like and possibly syphilis-like infections.

Analysis on Arctodus bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters with no evidence of ingestion of vegetation. A. simus was an obligate carnivore, and as an adult would have daily required 16 kg (35 pounds) of flesh to survive.

One theory of its predatory habits envisions Arctodus simus as a brutish predator that overwhelmed the large mammals of the Pleistocene with its great physical strength. This idea is considered problematic, as Arctodus, though very large, was quite gracile in build. In order to bring down fellow megafauna, this bear would have had to have been a more robust creature, with a denser skeletal structure. Other experts think the long-legged Arctodus was able to run down smaller Pleistocene herbivores such as steppe horses and saiga antelopes in a cheetah-like fashion. However, in this scenario, the bear’s sheer physical mass would be a handicap. Arctodus skeletons do not articulate in a way that would have allowed for quick turns, an ability required of any predator that survives by killing agile prey. Dr. Paul Matheus, paleontologist at the University of Alaska Fairbanks, determined that Arctodus' moved in a pacing motion like a camel or horse, making it built more for endurance than for great speed. Arctodus simus, then, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite, using its enormous size to intimidate smaller predators such as dire wolves, Smilodon and American lions from their kills.

Though seen by some as primarily a scavenger, its fearsome natural weapons could have allowed it to attack slow-moving animals such as the Megatherium, according to U.S. National Park Service paleontologist Greg McDonald. Despite being largely herbivorous, Megatherium might also have scavenged on carcasses, possibly as a competitor to Arctodus

The giant short-faced bear became extinct some 12 kya, perhaps partly because some of its large prey died out earlier, and partly also because of competition with the smaller, more omnivorous brown bears that entered North America from Eurasia. Since its demise coincides with the development of the Clovis technology and improved hunting techniques by humans in North America, hunting pressure may also have contributed to its extinction, both directly (human hunting) or indirectly (due to the depletion of other large mammals on which it may have followed for its kills or depended on as prey).

Updated 2010-10-30

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