Short-faced bear

Short-faced bear
Temporal range: Middle Pleistocene to Early Holocene, 1.8–0.010 Ma
↓
A. simus from the La Brea tar pits
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Subfamily: Tremarctinae
Genus: †Arctodus
Leidy, 1854
Type species
†Arctodus pristinus
Leidy, 1854
Species
  • †A. simus (Cope, 1879)
  • †A. pristinus (Leidy, 1854)

The short-faced bear (Arctodus spp.) is an extinct bear that inhabited North America during the Pleistocene epoch from about 1.8 Mya until 11,000 years ago. It was the most common early North American bear and was most abundant in California.[1] There are two recognized species: Arctodus pristinus and Arctodus simus, with the latter considered to be one of the largest known terrestrial mammalian carnivores that has ever existed. It has been hypothesized that their extinction coincides with the Younger Dryas period of global cooling commencing around 10,900 BC.

Naming and etymology

The name short-faced bear derives from the shape of their skulls, which appear to have a proportionally short snout compared to other bears; this characteristic is also shared by its extant relative the spectacled bear. However, this apparent shortness is an optical illusion caused by their deep snouts and short nasal regions.[2] The scientific name of the genus, Arctodus, derives from the Greek language and means "bear tooth".

Taxonomy, classification and evolution

The short-faced bear belongs to a group of bears known as the Tremarctinae, which appeared in the Americas during the earliest parts of the late Miocene epoch in the form of Plionarctos, a genus considered ancestral to Arctodus, Arctotherium and the modern spectacled bear (Tremarctos ornatus). Although the early history of Arctodus is poorly known, it evidently became widespread in North America by the Kansan age about 800,000 years ago.

Species

Restoration of Arctodus simus

Arctodus simus first appeared during the middle Pleistocene in North America, about 800,000 years ago, ranging from Alaska to Mississippi,[3][4] and it became extinct about 11,600 years ago. Its fossils were first found in the Potter Creek Cave, Shasta County, California.[5] It might have been the largest carnivorous land mammal that ever lived in North America. Only one Giant Short-faced Bear skeleton has been found in Indiana, unearthed south of Rochester on west of Nyona Lake on Chet Williams' farm.[6] It has become well known in scientific circles because it was the largest nearly complete skeleton of a giant short-faced bear found in America. The original bones are in the Field Museum, Chicago. The new Indiana State Museum, Indianapolis, and the Yukon Beringia Interpretive Centre, Whitehorse, Yukon Territory, Canada, have casts made of the bones.

In a recent study, the mass of six specimens was estimated, one-third of them weighed about 900 kg (1 short ton), the largest being UVP 015 at 957 kg (2,110 lb), suggesting specimens that big were probably more common than previously thought.[2] It stood 8–10 feet (2.4–3.0 m) tall on hind legs[7] while a large specimen would have been 11–12 feet (3.4–3.7 m) tall with a 14-foot (4.3 m) vertical arm reach, and 5–6 feet (1.5–1.8 m) high at the shoulder when walking on all fours, it was tall enough to look a man in the eye.[8][9][10] At Riverbluff Cave, Missouri, a series of claw marks up to 15 feet (4.57 m) high have been found along the cave wall indicating Short-faced bears up to 12 feet (3.66 m) tall.[11][12]

Arctodus pristinus inhabited more southerly areas, ranging from northern Texas to New Jersey in the east, Aguascalientes, Mexico[13] 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
Scale when compared to a human

Researchers disagree on the diet of Arctodus. Analysis of their bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters, with no evidence of ingestion of vegetation. Based on this evidence, A. simus was highly carnivorous and as an adult would have required 16 kg (35.3 lb) of flesh per day to survive.[7][14]

One proposal for its predatory habits envisages A. 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.

Because its long legs enabled it to run at speeds of 50–70 km/h (30–40 mph), an alternative hypothesis is that it may have hunted by running down Pleistocene herbivores, such as wild horses and saiga antelopes, in a cheetah-like fashion, at one time earning it the name "running bear".[15] However, during pursuit of speedy game animals, 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.[7]

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.[7] A. simus, according to these arguments, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite,[7] using its enormous size to intimidate smaller predators, such as Dire wolves, saber-tooth cat, and American lions, chase them from their kills and steal their food.

Some authors also suggest that the giant short-faced bear and the cave bear were omnivores, like most modern bears, and the former may have eaten plants depending on availability.[16]

See also

References

  1. ↑ Brown, Gary (1996). Great Bear Almanac. p. 340. ISBN 1558214747.
  2. 1 2 Figueirido; et al. (2010). "Demythologizing Arctodus simus, the 'short-faced'". Journal of Vertebrate Paleontology. 30 (1): 262–275. doi:10.1080/02724630903416027.
  3. ↑ C. S. Churcher, A. V. Morgan, and L. D. Carter. 1993. Arctodus simus from the Alaskan Arctic Slope. Canadian Journal of Earth Sciences 30(5):1007-1013, collected by A. V. Morgan
  4. ↑ M. L. Cassiliano. 1999. Biostratigraphy of Blancan and Irvingtonian mammals in the Fish Creek-Vallecito Creek section, southern California, and a review of the Blancan-Irvingtonian boundary. Journal of Vertebrate Paleontology 19(1):169-186
  5. ↑ COPE, E. D. 1879. The cave bear of California. American Naturalist, 13:791.
  6. ↑ Rochester's Giant Bear Gets Famous By Shirley Willard, Fulton County Historian
  7. 1 2 3 4 5 "The Biggest Bear ... Ever". Nancy Sisinyak. Alaska Fish and Wildlife News. Retrieved 2008-01-12.
  8. ↑ "Yukon Beringia Interpretive Centre". Retrieved 17 April 2014.
  9. ↑ "North American Bear Center". Extinct Short-faced Bear. Retrieved 17 April 2014.
  10. ↑ Brown, Gary (December 3, 2013). The Bear Almanac, 2nd: A Comprehensive Guide to the Bears of the World. Lyons Press. p. 8. ISBN 978-0762788064.
  11. ↑ "Bear Claw Marks". Riverbluff Cave - The Official Website. Retrieved 17 April 2014.
  12. ↑ "Cave Animals". Riverbluff Cave - The Official Website. Retrieved 17 April 2014.
  13. ↑ I. Ferrusquia-Villafranca. 1978. Bol Univ Nac Aut Mex Inst Geol 101:193-321
  14. ↑ National Geographic Channel, 16 September 2007, Prehistoric Predators: Short-faced bear, interview with Dr. Paul Matheus
  15. ↑ US National Park Service paleontologist Greg McDonald.
  16. ↑ ScienceDaily, 13 April 2009."Prehistoric Bears Ate Everything And Anything, Just Like Modern Cousins". ScienceDaily. Retrieved 2009-04-13.
This article is issued from Wikipedia - version of the 10/15/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.