64 Facts About Arctodus

Today considered to be an enormous omnivore, Arctodus simus is believed to be one of the largest known terrestrial mammalian carnivorans that has ever existed.

Arctodus belongs to the Tremarctinae subfamily of bears, which are endemic to the Americas.

Arctodus was first described by Joseph Leidy in 1854, with finds of A pristinus from the Ashley Phosphate Beds, South Carolina.

Conversely, fossils of Arctodus pristinus are often confused with the similarly sized, partially contemporaneous short-faced bear, Tremarctos floridanus.

Arctodus belongs to the subfamily Tremarctinae, which appeared in North America during the earliest parts of the late Miocene epoch in the form of Plionarctos, a genus considered ancestral to Tremarctinae.

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Tremarctos floridanus established a range mostly hugging the Gulf Coast, whereas Arctodus pristinus ranged from Aguascalientes, Mexico, to Port Kennedy, Pennsylvania, in the US.

However, in the early Quaternary, when both Borophagus and Agriotherium went extinct, Arctodus would take advantage and spread into the rest of the continent, primarily in the form of A simus.

Likewise, Arctodus simus is relatively poorly known from the Irvingtonian with finds mostly from California, with additional remains from Texas, Kansas, Nebraska, and Montana.

The orbits of Arctodus are proportionally small compared to the size of the skull, and somewhat laterally orientated, more so than actively predatory carnivorans or even the brown bear, suggesting that stereoscopic vision was not a priority.

Premolars and first molars of Arctodus pristinus are relatively smaller and more widely spaced than those of Arctodus simus.

The dentition of Arctodus has been used as evidence of a predatory lifestyle- in particular the large canines, the high-crowned lower first molar, and the possible carnassial shear with the upper fourth premolar.

Paws of Arctodus were characteristically long, slender, and more elongated along the third and fourth digits compared to ursine bears.

Arctodus' paws were therefore more symmetrical than ursine bears, whose feet have axes aligned with the most lateral digit.

The trackways suggest that Arctodus had an oval-shaped, undivided pad on its sole, with front paws that were slightly larger than its back paws, possessed long claws, and had its hind foot overstep the forefoot when walking, like modern bears.

Presence of a partial false thumb in Arctodus simus is a characteristic shared with Tremarctos floridanus and the spectacled bear, and is possibly an ancestral trait.

Arctodus probably had an even shorter back than other bears, due the necessary ratio between body length and body mass of the huge bear.

Sometimes referred to as the eastern short-faced bear, Arctodus pristinus has been found in Kansas, South Carolina, Maryland and Pennsylvania in the US, and Aguascalientes in Mexico.

Arctodus pristinus is particularly well known from Florida, especially from the Leisey Shell Pit.

Arctodus pristinus is considered a biochronological indicator for the period between the Late Blancan and late Irvingtonian periods of Pleistocene Florida.

Occasionally referred to as the great short-faced bear, Arctodus simus was particularly plentiful in western North America.

Typically thought of as an open habitat specialist, Arctodus seems to have been abundant in mixed habitat where C3 vegetation was available.

Brown bears and Arctodus have been discovered together in Alaska before ~34,000 BP, and in later Pleistocene deposits in Vancouver Island, Wyoming and Nevada.

Female specimens of Arctodus simus have been inferred to have been exhibiting maternal denning, however the expression of metabolic denning is unclear in Arctodus.

One hypothesis suggests the Fulton County Arctodus specimen suffered from a syphilis-like disease, or yaws, based on lesions on the vertebrae, ribs and both ulnae.

Arctodus simus was limited to the Mexican plateau, which was generally occupied by tropical thorn scrub and scrub woodland.

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At La Cinta-Portalitos in the Trans-Mexican Volcanic Belt, prime habitat for Arctodus simus was the closed temperate forests of the Madrean pine–oak woodlands, dominated by pines, oaks, hornbeams, and ferns.

Similar highland Arctodus simus remains have been recovered from Zacoalco, Valsequillo, and Tequixquiac.

The earliest finds of Arctodus simus are from California, from early and middle Irvingtonian age sites such as Vallecito Creek, Irvington, Riverside, and Fairmead.

Should Arctodus have been a predator, competition with closed habitat, browser specialists would have included Smilodon and Panthera atrox in Late Pleistocene inland California.

Notable fauna which lived alongside Arctodus simus included Shasta ground sloth, shrub-ox, pronghorns, Camelops, Odocoileus, horses, Lynx, puma, black bear, mountain goats, prairie dogs, and Stock's vampire bat.

However, one of the youngest dated Arctodus simus is from a cave near Huntington Reservoir, Utah, which sits at an elevation of 2,740m,.

Arctodus simus co-existed with ground sloths, Pacific mastodon, camels, and oxen.

Beyond Texas, Arctodus has been found from the Kaw River and Jinglebob in Kansas.

Sympatry between the two species is most apparent in Missouri- Arctodus simus has been found in association with black bears at Riverbluff, Bat and Big Bear caves.

Heavy bone damage on a mammoth carcass by both dire wolves and Arctodus suggests a potentially competitive scavenging relationship Additional remains have been found at Island Ford Cave in Virginia, and Frankstown in Pennsylvania.

Furthermore, the abundance of black bears, and particularly Florida short faced bears in Florida, has led to a theorized niche partitioning of ursids in Florida, with Tremarctos floridanus being herbivorous, and black bears and Arctodus simus being omnivorous, with Arctodus being possibly more inclined towards carnivory.

Arctodus simus remains have been recovered from the mid-Wisconsian near Edmonton, forming a predator guild with the gray wolf and American lion.

Arctodus remains from similar habitat has been recovered from Saskatchewan, and from the forest-steppe of Late Pleistocene Vancouver Island.

The idea that Arctodus had a kleptoparasitic relationship with wolves and Homotherium in Beringia has been explored, and with the additional possibility that Arctodus restricted brown bears and Homotherium access to caribou pre-LGM.

Arctodus skeletons do not articulate in a way that would have allowed for quick turns – an ability required of any predator that survives by chasing down agile prey.

However, analysis of the forelimb of Arctodus suggests the bear could have been in the early stages of cursorial evolution- A simus was somewhat more prone to cursorial tendencies, being capable of more efficient locomotion, A simus was interpreted as capable of high-speed, straight-line locomotion, and was likely more adept at pursuing large prey than the extant polar and brown bears.

Idea that Arctodus was a kleptoparasite was most notably proposed by Paul Matheus.

Additionally, the short, broad rostrum of Arctodus is a characteristic shared with the sun bear and the spectacled bear, which are both omnivorous.

Furthermore, the relative lack of Arctodus remains at predator traps such as the La Brea Tar Pits, suggests that Arctodus did not compete for carcasses.

Arctodus simus plotted in between the likely hypercarnivorous Cephalogale, and the obligately herbivorous Eurasian cave bear and Indarctos, suggesting omnivory.

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Arctodus follows a similar eco-morphology- while much evidence suggests herbivory, isotope data from some populations of Arctodus suggests the regular consumption of meat.

Secondly, the spectacled bear, the closest living relative of Arctodus, is a herbivorous short-faced bear- both bears have been noted to share various adaptations for herbivory.

Arctodus simus resembled these two living hyaenids, along with the predatory spotted hyena, in skull shape and relative lengths of the trunk, back and limbs.

However, it is equally possible that the longer limbs of Arctodus simus were used in tearing and pulling down vegetation, including shrubs and small trees, in order to feed on leaves, fruits, bark, seeds and flowers.

Fact that Arctodus did not significantly differ in dentition or build from modern bears has led most authors to support the hypothesis that the A simus and the cave bear were omnivores, like most modern bears, and the former would have eaten plants depending on availability.

Fossils of bear coprolites found in association with Arctodus remains at The Mammoth Site in South Dakota are believed to contain Juniperus seeds.

Paleontologists Steven Emslie and Nicholas Czaplewski suggested that the body size of Arctodus simus exceeded the expected upper limitations for a Quaternary terrestrial carnivore.

However, the gracility and lack of agility of Arctodus would have complicated predation upon adult mega-herbivores, and hindered the chasing down of nimbler prey.

Additionally, studies of mandibular morphology and tooth microwear of bears confirms that short faced bears such as the spectacled bear and Arctodus were adapted to and actively consumed vegetation, whereas Ursus is omnivorous.

The dC value showed that this individual fed upon C3 resources- in fact, that Arctodus individual had the strongest dC value of the fauna studied.

Specimens from inland California from the Middle Pleistocene, a 2012 study proposed that Arctodus simus consumed Colombian mammoth, and large ungulates- that Arctodus likely consumed substantial amounts of vegetation made conclusive determinations unclear.

Arctodus simus has been found in association with proboscidean remains near Frankstown, Pennsylvania, and at The Mammoth Site, South Dakota.

Additionally, the isotope data purportedly establishing the carnivory of Beringian Arctodus overlapped with modern, omni-herbivorous brown bears from Europe, eastern Wyoming, and central Montana, demonstrating that isotope data cannot distinguish between hypercarnivores and omnivores which eat a significant amount of animal matter.

Additionally, other remains of the Arctodus simus have been found in association with Paleo-Indian artifacts in Sheriden Cave, Ohio, and Huntington Dam, Utah.

Additionally, the human colonization of North America south of the ice sheets further disproves the idea that Arctodus was a migration barrier.

Arctodus simus went extinct around 12,000 years ago, which was relatively late when compared to other victims of the Quaternary extinction event.

Arctodus was one of the last North American megafauna to go extinct, having reached the Pleistocene-Holocene boundary.

Correspondingly, Arctodus simus had a very low level of genetic diversity from most sampled specimens, albeit a sample with a Beringian and temporal bias.

Youngest date for Arctodus simus is circa 12,700 BP from Friesenhahn Cave, Texas, calibrated from 10,814 ± 55 radiocarbon years.