Arctodus

Arctodus is an extinct genus of short-faced bear endemic to North America during the Pleistocene era about 2.5 million years ago to 12,800 years ago. There were two species, Arctodus pristinus and Arctodus simus.

Arctodus Temporal range: Pleistocene 2.5–0.0128 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
A. simus from the La Brea tar pits
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Ursidae
Subfamily:	Tremarctinae
Genus:	†Arctodus Leidy, 1854
Type species
†Arctodus pristinus Leidy, 1854
Species
†A. pristinus (Leidy, 1854) †A. simus (Cope, 1879)
Maximum range of Arctodus simus.

The giant short-faced bear, Arctodus simus, evolved from Arctodus pristinus during the middle Pleistocene of North America, around 1.3 million years ago. Both species were omnivorous, feeding on tall vegetation and large mammals. Arctodus simus might have been the largest predatory land mammal that ever lived in North America.

Habitat

Both species of Arctodus lived in different habitats, with Arctodus pristinus preferred dense forests in eastern North America,^[1] and Arctodus simus inhabiting open forests in western North America. However, after the extinction of Arctodus pristinus, the giant short-faced bear spread east in small numbers.^[2]

Arctodus pristinus was particularly common on the east coast, with the largest concentrations being in Florida.^[3] Additional finds are from Pennsylvania, West Virginia, Kansas and Aguascalientes (Mexico).^[4][5]

Arctodus simus lived in much of North America, ranging from Alaska to Puebla in the west,^[6] to Virginia and Florida in the east.^[2][5] This species is first found in California,^[5][7] and was most common in the savannas and pinon-juniper woodlands of the western United States and Mexico, where many other megafauna lived.^[8][9]

Fossils

The oldest Arctodus fossils are from the Kissimmee River & Santa Fe River paleontological sites in Florida, belonging to Arctodus pristinus.^[3] The first fossils of the Arctodus simus were found the Potter Creek Cave in Shasta County, California, by Edward Drinker Cope,^[10] with the oldest being from Irvington, California.^[5]

Paleontologists have found only one Arctodus simus skeleton in Indiana.^[11] It is famous because it was the biggest most-nearly complete skeleton of a giant short-faced bear ever found in America. The original bones are in Chicago's Field Museum of Natural History.^[12]

Males were much larger than females.^[13] When it was standing on its back legs, Arctodus simus was 8–11 feet (2.4–3.4 m) tall.^[14] A 2010 study estimated the weight of six Arctodus simus individuals, with a weight range between 317 kg (699 lb) and 957 kg (2,110 lb). In comparison, Arctodus pristinus specimens have been calculated to an average of ~133 kg (293 lb),^[15] although some northern and western Arctodus pristinus were the same size as small Arctodus simus.^[5]

Behavior

Both species were omnivores, browsing on shrubs and trees, and eating browsers like deer, camels, llamas, tapirs, ground sloths, and wood bison,^[16][17] Dental damage from eating carbohydrates,^[18][19][20] and seeds in Arctodus simus' poop proves plants were consumed,^[21][22] while bone damage on prey matches both Arctodus species' teeth.^{[13][23][24][25]} Analyses of Arctodus simus' bone chemicals confirm that the giant short-faced bear lived in open forests and other vegetated areas, and sometimes ate other open forest inhabitants.^{[17][26][27][28][29][30]}

The skeleton of Arctodus pristinus, from The Bishop Museum of Science and Nature, Florida.

Past research

One theory was that the giant short-faced bear was an active predator, attacking herbivores directly.^[31] Another theory was that it let faster predators make the kill, then bullied them off the carcass, being a scavenger.^[32] Finally, anatomy led some to believe it was a herbivore.^[33] Modern research establishes all three behaviors were present in Arctodus simus.^[16]

Previous theories also suggested that brown bears caused the extinction of Arctodus simus, and that the giant short-faced bear prevented people from migrating into North America.^[34] However, these ideas have been rejected,^[35] with new dates confirming both co-existed with Arctodus simus.^[36][37]

Extinction

The replacement of hot & humid forests with open habitats, along with competition with black bears and Tremarctos floridanus, led to the extinction of Arctodus pristinus 300,000 years ago.^[3] Arctodus simus went extinct around 12,800 years ago,^[38][39] which was likely due to ecological collapse leading to fewer prey and quality vegetation.^[34]