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_.

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, 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.

_Arctodus pristinus_ was particularly common on the east coast, with the largest concentrations being in Florida. Additional finds are from Pennsylvania, West Virginia, Kansas and Aguascalientes (Mexico).

_Arctodus simus_ lived in much of North America, ranging from Alaska to Puebla in the west, to Virginia and Florida in the east. This species is first found in California, and was most common in the savannas and pinon-juniper woodlands of the western United States and Mexico, where many other megafauna lived.

## Fossils

The oldest _Arctodus_ fossils are from the Kissimmee River & Santa Fe River paleontological sites in Florida, belonging to _Arctodus pristinus._ The first fossils of the _Arctodus simus_ were found the Potter Creek Cave in Shasta County, California, by Edward Drinker Cope, with the oldest being from Irvington, California.

Paleontologists have found only one _Arctodus simus_ skeleton in Indiana. 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.

Males were much larger than females. When it was standing on its back legs, _Arctodus simus_ was  tall. A 2010 study estimated the weight of six _Arctodus simus_ individuals, with a weight range between  and . In comparison, _Arctodus pristinus_ specimens have been calculated to an average of ~, although some northern and western _Arctodus pristinus_ were the same size as small _Arctodus simus_.

## Behavior

Both species were omnivores, browsing on shrubs and trees, and eating browsers like deer, camels, llamas, tapirs, ground sloths, and wood bison, Dental damage from eating carbohydrates, and seeds in _Arctodus simus_' poop proves plants were consumed, while bone damage on prey matches both _Arctodus_ species' teeth. Analyses of _Arctodus simus_<nowiki/>' bone chemicals confirm that the giant short-faced bear lived in open forests and other vegetated areas, and sometimes ate other open forest inhabitants.

## Past research

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

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. However, these ideas have been rejected, with new dates confirming both co-existed with _Arctodus simus_.

## 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. _Arctodus simus_ went extinct around 12,800 years ago, which was likely due to ecological collapse leading to fewer prey and quality vegetation.