Arctodus
| Short-faced bears Temporal range: Middle to Late Pleistocene
| |
|---|---|
| |
| A. simus from the La Brea tar pits | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Order: | |
| Family: | |
| Subfamily: | |
| Tribe: | |
| Genus: | †Arctodus Leidy, 1854
|
| Species | |
| |
The short-faced bear or bulldog bear or "Xuyang", or Arctodus (Greek, "bear tooth"), is an extinct genus of bear endemic to North America during the Pleistocene ~3.0 Ma. – 11,000 years ago, existing for approximately three million years. Arctodus simus may have once been Earth's largest mammalian, terrestrial carnivore. The species described are all thought to have been larger than any living species of bear. It was the most common of early North American bears, being most abundant in California.[1]
Taxonomy, classification and evolution
The short-faced bears belonged to a group of bears known as the tremarctine bears or running bears, which have been found in the Americas and Europe. The earliest member of the Tremarctinae was Plionarctos edensis, which lived in Indiana and Tennessee during the Miocene Epoch (10 mya). This genus is considered ancestral to Arctodus, as well as to the modern spectacled bear, Tremarctos ornatus. Tremarctos floridanus was a contemporary. 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). The South American genus Arctotherium, was the closest relative to Arctodus and it had similar short faced adaptions and reached similar or greater sizes.[2]
Species
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. It was first found in the Potter Creek Cave, Shasta County, California.[5] It was the largest carnivorous mammal that ever lived in North America; in a recent study, the mass of 6 specimens was estimated, one third of them weighed about 900 kg (0.99 short tons)*, the largest being UVP 015 at 957 kg (2,110 lb), suggesting that specimens that big were probably more common than previously thought.[6] Furthermore, claw marks reaching heights of up to 4.6 m (15 ft) on the walls of the Riverbluff Cave are indicative of the great size of the short-faced bears who made them.[7]
Arctodus pristinus (3 to 2.2 Ma.), a species with 2 specimens weighing 500.7 kg (1,100 lb) and 63.6 kg (140 lb)[8] inhabiting more southern areas from northern Texas to New Jersey in the east, Aguascalientes, Mexico[9] 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
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.[10][11]
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.[12] 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.[11] 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.[11] Arctodus simus, according to these arguments, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite,[11] using its enormous size to intimidate smaller predators such as dire wolves, Smilodon and American lions from their kills.
Some authors also suggest that the giant short-faced bear as well as the cave bear were omnivores like most modern bears, and that the former did eat plants depending on availability.[13]
Extinction
The giant short-faced bear became extinct about 12,000 years 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
References
- ^ Brown, Gary (1996). Great Bear Almanac. p. 340. ISBN 1558214747.
- ^ Soibelzon, L. H. (2011-01). "The Largest Known Bear, Arctotherium angustidens, from the Early Pleistocene Pampean Region of Argentina: With a Discussion of Size and Diet Trends in Bears". Journal of Paleontology. 85 (1). Paleontological Society: 69–75. doi:10.1666/10-037.1. Retrieved 2011-06-01.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ 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
- ^ 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
- ^ COPE, E. D. 1879. The cave bear of California. American Naturalist, 13:791.
- ^ Figueirido; et al. (2010). "Demythologizing Arctodus simus, the 'short-faced'". Journal of Vertebrate Paleontology. 30 (1): 262–275. doi:10.1080/02724630903416027.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ "Riverbluff Cave - The Official Website".
- ^ S. Legendre and C. Roth. 1988. Correlation of carnassial tooth size and body weight in recent carnivores (Mammalia). Historical Biology 1(1):85-98
- ^ I. Ferrusquia-Villafranca. 1978. Bol Univ Nac Aut Mex Inst Geol 101:193-321
- ^ National Geographic Channel, 16 September 2007, Prehistoric Predators: Short-faced bear, interview with Dr. Paul Matheus
- ^ a b c d "The Biggest Bear ... Ever". Nancy Sisinyak. Alaska Fish and Wildlife News. Retrieved 2008-01-12.
{{cite web}}: Italic or bold markup not allowed in:|publisher=(help) - ^ U.S. National Park Service paleontologist Greg McDonald.
- ^ ScienceDaily, 13 April 2009. "Prehistoric Bears Ate Everything And Anything, Just Like Modern Cousins". ScienceDaily. Retrieved 2009-04-13.