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. 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.* with the oldest being from Irvington, California. 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*. 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*' 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*. 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. which was likely due to ecological collapse leading to fewer prey and quality vegetation.

## References