Arctodus simus

Arctodus simus

Taxobox
name = "Arctodus simus"
fossil_range = Middle to Late Pleistocene



image_width = 240px
image_caption = A 1.6 m tall "Arctodus simus" next to a 1.8 m human.
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Carnivora
familia = Ursidae
subfamilia = Tremarctinae
genus = "Arctodus"
species = "simus"
binomial = "A. simus"
species="Arctodus simus", Cope 1897
binomial_authority = (Cope, 1897)
range_

range_map_width = 200px
range_map_caption = Range of "Arctodus simus"

"Arctodus simus", also known as the giant short-faced bear is an extinct species of bear. The genus "Arctodus" is known as the short-faced or bulldog bears. "A. simus" is likely the largest bear that ever lived. It was native to prehistoric North America from about 12.5-800 kya.

Taxonomy, classification and evolution

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).

Physiology

"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.cite book | author= Macdonald, David | title=The Velvet Claw | year=1992 | pages= 256 | id=0563208449 ] The largest specimens were found in Alaska and the Yukon Territory.cite book | author = Brown, Gary | title = Great Bear Almanac | year = 1996 | pages = pp.340 | id = ISBN 1558214747] Males were 20% bigger than females.cite web | url =http://www.beringia.com/02/02maina4.html| title = North American Short-Faced Bear | work = Harrington, C.R| publisher = Yukon Beringia Interpretive Centre| accessdate = 2008-01-14] 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.National Geographic Channel, 16 September 2007, "Prehistoric Predators: Short-faced bear", interview with Dr. Paul Matheus] cite web | url =http://www.wc.adfg.state.ak.us/index.cfm?adfg=wildlife_news.view_article&articles_id=232&issue_id=41| title = "The Biggest Bear ... Ever" | work = Nancy Sisinyak | publisher = "Alaska Fish and Wildlife News" | accessdate = 2008-01-12]

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.

Range

"A. simus" was native to North America, where it ranged from the north central plains -- Alaska and Canada -- to central Mexico, and California to Virginia. It was the most common of early North American bears, being most abundant in California. cite book | author = Brown, Gary | title = Great Bear Almanac | year = 1996 | pages = pp.340 | id = ISBN 1558214747]

Dietary habits

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".cite web | url = http://www.bbc.co.uk/nature/wildfacts/factfiles/456.shtml| title = "BBC > Science & Nature > Wildfacts > Megatherium" | publisher = "BBC - Science & Nature" http://www.bbc.co.uk/sn/ | accessdate = 2008-07-18]

Extinction

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).

In media

The short-faced bear appears in "" as an adoptable animal available at Four Stars Zoo fame.Fact|date=July 2008 It also appears in a BBC documentary titled "Monsters We Met" (also known as "Land of Lost Monsters" and "Wild New World") and the History Channel's Jurassic Fight Club (episode "Ice Age Monsters").

References

ee also

*Pleistocene extinctions
*Pleistocene megafauna

External links

* [http://www.uaf.edu/news/a_news/20041111132847.html U. of Alaska-Fairbanks: Matheus, Ancient fossil offers new clues to brown bears past]
* [http://www.igorn.com/trip2001/pics/092901/beringia3.jpgAn artist's impression of an Arctodus]
* [http://www.wc.adfg.state.ak.us/index.cfm?adfg=wildlife_news.view_article&articles_id=232&issue_id=41 The Biggest Bear ... Ever]
* [http://www.beringia.com/02/02maina4.html Yukon Beringia Interpretive Centre]


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