Arctodus

Short-faced bears Temporal range: Middle to Late Pleistocene
A. simus from the La Brea tar pits
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Ursidae
Subfamily:	Tremarctinae
Tribe:	Tremarctini
Genus:	†Arctodus Leidy, 1854
Species
A. simus Cope, 1897 † A. pristinus †

Arctodus (which translates as Bear Tooth) — known as the short-faced bear or bulldog bear — is an extinct genus of bear endemic to North America during the Pleistocene ~3.0 Ma.—11,000 years ago, existing for approximately 2.989 million years. It was the most common of early North American bears, being most abundant in California.

Taxonomy, classification and evolution

Restoration of Arctodus simus

The short-faced bears but head.north amerighyiryhiyiyt

Species

A. simus compared to a human in size

Arctodus simus (2.0—1.9 Ma.), a species with 2 specimens weighing 110.2 kg (240 lb) and 800 kg (1,800 lb) as noted by Legendre and Roth, inhabiting a generally more northern and larger range. It was native to prehistoric North America from about 800,000 years ago, and became extinct about 12,500 years ago. It has been found from as far north as Ikpikpuk River, Alaska to Lowndes County, Mississippi. It is one of the largest bears in the fossil record and was among the largest mammalian land predators of all time. The type specimen came from Potter Creek Cave in Shasta County, California. Males from the Yukon region - the largest representatives of the species - would have stood about 1.80 m (5.9 ft) at the shoulder (on all fours), 4 m (13 ft) upright and may have weighed about 800 kg (1,800 lb).

Arctodus pristinus (3.0—2.2 Ma), a species with 2 specimens weighing Template:Asderrrff and 63.6 kg (140 lb) inhabiting more southern areas from northern Texas to New Jersey in the east, Aguascalientest, Mexico to the southwest, and with large concentrations in Florida, the oldest from the Santa Fe River 1 site of Gilchrist County, Florida paleontological sites.

Dietary habits

Arctodus skull

Researchers disagree on the diet of Arctodus. Analysis of Arctodus bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters, with no evidence of ingestion of vegetation. Based upon this evidence A. simus was highly carnivorous, and as an adult would have required 16 kilograms (35.3 lb) of flesh per day 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. However, despite being very large its limbs were too gracile for such an attack strategy. Alternatively, long legs and speed (50–70 kilometres per hour (30–40 mph)) may have allowed it to run down 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, horse, and modern bears, making it built more for endurance than for great speed. Arctodus simus, according to these arguments, 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.

Recently, closer dietary research on the giant short-faced bear as well as the Cave Bear suggests that both bears were omnivores like most modern bears, and that the former did eat plants depending on availability.

Extinction

The giant short-faced bear became extinct some 12 millennia ago, 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 which it may have followed to scavenge kills or depended upon as prey).

See also

• Pleistocene megafauna