Extinct Short-faced Bear (Actodus spp.) Fact Sheet: Physical Characteristics

Careful study of fossil bone or tooth anatomy yields much exact information about placement and strength of muscles, tendons, ligaments, nerves, and blood vessels. In rare cases, skin and hair impressions or actual skin or hair is preserved. Body weight is more difficult to gauge because fat leaves no impression on the skeleton.

* For comparison, an average male polar bear's weight is about 600 kg (1323 lb) and may be up to 800 kg (1,764 lb); a Brown Bear's weight varies with diet but is generally less than that of a Polar Bear.

Note: Estimates in literature vary widely for Arctodus; this is a highly dimorphic species, as are living bears, with extreme differences between males and females; many estimates based on very small sample sizes

Body size

Arctodus simus is an enormous extinct bear with a domed skull, wide snout, a short back, with tooth and jaw features that suggest omnivorous habits. (Figueirido et al 2010)

• Recent studies indicate it is not particularily short-faced for a bear its size and its legs are not long compared to other bears as previously asserted.
• The common name (the "Short-faced Bear") is misleading.

Arctodus simus was the largest Pleistocene carnivore on land.

A. pristinus was much smaller, with a similar proportions.

Teeth 

• Cheek teeth are well-developed and relatively tall (Figueirido et al 2009)
• Canine teeth massive but short compared to some other bears. (Figueirido et al 2009) (Sorkin 2006)
• Wear patterns on on first molars are not like those of a typical carnivore such as a wolf. (Sorkin 2006)

Pelage  

• Unknown

Distinct sexual dimorphism; males are about 15% larger than females.

The living tremarctine bear, Tremarctos, has 53 chromosomes; all other bears have 74.

Bones are quite light for their size.

Toes align forward, rather than inward as in other bears.

Feet are plantigrade (walked flat-footed)

Fingers have a small bone in the wrist, the radial sesamoid, which is enlarged, forming a "false thumb" somewhat similar to that of the giant panda and the spectacled bear (Salesa et al 2006)

• This normally small bone is enlarged, acting as an opposable thumb that allows easier manipulation of plant food.
• This bone can also aid in tree climbing as seen in the giant panda.
• This bone is small in meat-eating bears.

The articulation of the lower and upper jaws falls above the tooth row, as in plant-eating hoofed mammals. (Sorkin 2006)

Eye sockets are small and directed somewhat to the side, similar to those of plant-eating hoofed mammals. (Sorkin 2006)

Christiansen (1999)
Figueirido et al (2009)
Figueirido et al (2010)
Garshelis (2009)
Kurtén & Anderson (1980)
Salesa et al (2006)
Sorkin (2006)