Kara waits for salmon.
(c) 2004. S. Stringham
LIFE IN THE TREES
Bears evolved from dog-like ancestors that ate mainly meat. Prey can be difficult and dangerous to catch; and an animal can’t miss many meals without weakening. When meat is scarce, there’s much to be said for being able to subsist on vegetation. That’s precisely the direction prehistoric bears evolved, shifting from being carnivores to omnivores. The earliest species were small-bodied and able to climb trees to forage on energy- and nutrient-rich fruit and nuts, or to take refuge from enemies. Other ursine adaptations for life in trees are the short, sharp, hooked finger and toe claws, as well as heavy-boned limbs with relatively long, thickly muscled upper arms and thighs. This strategy has worked so well over recent aeons that most bear species today are still semi-arboreal: North American and Eurasian black bears, as well as sun, sloth bears, and spectacled bears. (For more on bear evolution, click here).
BEARS AND PRIMATES
In this respect, forest bears are similar to great apes. There are numerous anatomical similarities between bears and certain primates. In addition to structure of the limb bones, other similarities include:
1. Binocular vision for better depth perception
2. Color vision for better perception of stationary objects, especially colored fruits.
3. Dark pelage (hair/fur) in many forest species (e.g. North American and Asian black bears, sun bear, sloth bear, spectacled bear; gorilla, chimpanzee, bonobo, some gibbons and simangs).
4. High manual dexterity. A bear’s forepaws are essentially hands. Although bears lack an opposable thumb, they do have wrist bones which serve as pseudo thumbs. Pandas have two such bones; other bears have one -- as detailed on p. 7.
5. Ability to stand and sometimes walk bipedally.
Some bears also paralleled the ancestors of certain primates, including baboons and humans, by making the transition from forested habitats to ones where trees were scarce.
LIFE ON THE PLAINS
The ursine arboreal lifestyle was superbly successful in forested habitats, especially in moist climates. But nuts and fruit – except berries – are scarce where trees are scarce. To survive on the plains or steppes, bears had to exploit other foods such as roots, tubers, corms, and bulbs – all of which have to be dug up. That need favored evolution of longer, broader, straighter claws (as we also see in other mammals specialized for digging, such as dogs and badgers), as well as heavier arm and shoulder muscles. This combination of challenges and adaptations gave rise to the grizzly/brown bear -- which in turn gave rise to the polar bear.
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