Morphology

This section provides background on the physical configuration of bears. This is presented under the broad heading of Morphology, which derives from the ancient Greek "morphe," meaning "form." Most (but not all) of what I feature here pertains to the skeletal infrastructure of bears and, more specifically, to what makes them unique, especially among carnivores. I focus on the skeleton because in many ways it embodies a species' niche and the evolutionary forces that configured the animal in relationship to its environment and other species. So...looking at the shape and size of the skeleton can tell you a lot about what the animal is "designed" to do. (And, here, I take liberties is ascribing purpose to evolutionary forces simply as an efficient way of conveying the notion that adaptations yield comparative advantages that allow a species--at least for a while--to sustain itself in the face of predation, competition, and adverse physical environments).

 

So, in a thumbnail, what makes a bear "a bear,"--at least in terms of infrastructure and appearance? A number of things. Emphasizing the distinctive:

 

  • First, bears are large.--as a group, the largest of all the extant carnivores. The only rivals to this claim are the lion and tiger. Large size engenders many consequences, including demands placed on the skeleton to carry around a lot of weight.

  • Second, bears are fat--among the most corpulent of all terrestrial mammals. The hibernating bear species of northern latitudes have 20 to in excess of 30% body fat, in contrast to a median tendency of roughly 5% (3-10% interquartile range) among other land-dwelling mammals. The obesity of bears gives them a round portly appearance. The body fat also imposes costs, including the energetic expense of carting around so much extra weight, plus losses of speed and endurance. But the payoff is an ability to survive extended food shortages, including the figurative famine of hibernation.

  • Third, bears have exceedingly strong front quarters that manifest in a scapula and bones of the front limb that are robust even accounting for their size. These powerful front quarters facilitate a life of climbing, digging, or grappling with large prey.

  • Fourth, bears are quite dexterous, especially given their size. Of large land mammals, probably only the gorilla and orangutan exceed them in this regard. This dexterity provides bears with considerable facility at grasping, manipulating, and extracting foods. Such facility is carried to its extremes in the giant panda (Ailuropoda melanoleuca), which sports a "thumb" (an enlarged and mobile radial sesamoid bone in its paw) that allows it to efficiently handle bamboo--it's primary food.

  • Fifth, bears have large brains and small eyes, which correlate, in the first case, with considerable intelligence and, in the latter case, with comparatively underdeveloped eyesight. Parenthetically, anatomical evidence is ambiguous insofar as sense of smell is concerned. The majority of evidence suggests that bears are no more gifted in this regard than most carnivores--less so, perhaps, than dogs. The minority suggests otherwise--that bears do, in fact, have an acute sense of smell.

  • Sixth, bears lack a tail, which clearly differentiates them from the dogs (canids) and cats (felids). The bears presumably lack this feature because their lack of dependence on high maneuverability at fast speeds negates the benefits of carrying around an elongate appendage on their hind end.

  • Finally, bears are extremely small at birth relative to the size of their moms; among the smallest of all placental mammals. This correlates with being "altricial"--relatively helpless, and late in opening their eyes. As a result, bears (especially females) grow comparatively rapidly to reach adult weight during their first several years of life.

 

Turning to distinguishing features of brown (or grizzly) bears (Ursus arctos):

 

  • Brown bears are perhaps self-evidently "brown," at least as a dominant theme when it comes to the color of their coat (or pelage). That said, "brown" bears can vary in color from near black to lighter shades that are best described as blonde, gray, or silver. The extreme in this regard is the "blue" bear of Tibet (considered by some to be a separate subspecies, Ursus arctos pruinosus). This variant can look downright variegated, with pronounced patches of near white in juxtapose with light brown to grayish hindquarters.

  • Brown bears also tend to sport guard hairs with light nearly translucent tips, which has resulted in populations with lighter-colored hairs being described as "grizzled." Hence, the North American grizzly bear.

  • Brown bears have especially robust muscles surmounting their scapula, which gives them a distinctive hump over their shoulders. This hump can readily differentiate them from the black bears (Ursus americanus and U. thibetanus) with which they often co-occur in North America and eastern Asia.

  • Finally, brown bears have relatively long claws compared to other bears species. This is most pronounced among Tibetan brown bears, and least pronounced among European populations and the exceptionally large salmon-eating bears of the Pacific coast. Claw length seems to correlate with the extent to which brown bears are regionally dependent on excavated foods such as roots and underground-dwelling rodents, squirrels, and pikas.

 

I end this introductory section with a comment on what doesn't distinguish bears: most notably, their skull and jaw (                               ), at least in the sense that bear skulls do not exhibit any extreme features when compared to other carnivores. They have the forward-looking eyes and stereoscopic vision of virtually all carnivores, which surmount or partly straddle the snout (or rostrum), much like other carnivores as well. Although their skulls tend to be robust, they are not more robust than those of many other carnivores species--with the notable exception of the strongly-built skull of the bamboo-eating (crushing and grinding) giant panda. Their snout is neither extremely long nor extremely short, even among the shorter-faced species. Their teeth are also not highly specialized, certainly not as much as the meat-shearing (carnassial) teeth of cats. A bear's teeth reflects adaptations to a generalized omnivorous diet, although variation among bear species ranges from better developed meat-shearing cusps on the molars of the carnivorous polar bear to robust flat-topped (or bunodont) molars deeply anchored in the jaws of the more herbivorous giant panda and South American spectacled bear (Tremarctos ornatus).