From the somewhat incomplete fossil record, paleontologists believe that the \Pancestors\p of modern bears began to evolve early in the \POligocene\p epoch, some thirty to forty million years ago, as one of several groups of small animals branching from \Pcarnivorous\p tree climbers called \Pmiacids\p. From this same \Pprimeval\p stock are descended a second group, the raccoons and coatis, and a third comprising the canine species -- wolves, foxes, coyotes, and dogs.
\BDescription:\b An illustration of bear print fossils.
\BDrawing:\b William Bourke
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"Bears",2,faoy0390.bmp,b,015.wav
All three modern groups -- bears, raccoons, and canines -- are exceptionally intelligent by comparison with most other mammals, yet the ancestral \Pmiacids\p had small brains relative to their body size and could not have been blessed with comparable intelligence. A possible explanation of this paradox is the theory that \Pprimeval\p \Pprey\p was easy to capture, but during the ensuing millions of years some of the \Pprey\p species became more wary and elusive.
As the \Pprey\p became "smarter," natural selection favored more efficient predators, and the bears, raccoons, and canines survived by evolving larger, better-developed brains.
\BDescription:\b 19th century engraving of a raccoon.
\BDrawing:\b All Our Yesterdays
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"Oldest Known Bear",3,beartabl.bmp,d,016.wav
Some paleontologists hold that the oldest known creature that legitimately could be called a bear was \IUrsavus elemensis,\i a dog-sized predator inhabiting \Psubtropical\p Europe some twenty million years ago. Larger, more bearlike bears existed about six million years ago, and soon (that is, soon in geological terms) evolved into many forms, a few of them gigantic. However, many of those species met with extinction, probably doomed by changing climate and habitat.
Our modern bears are thought to be descended from a relatively small animal, \IProtursus,\i which, before it became extinct, finally gave rise to the modern genus \IUrsus\i two to three million years ago. Its descendants splintered into three lineages, one in Europe that was the \Pprogenitor\p of the extinct cave bear, \IU. spelaus,\i and two in Asia that brought forth today's brown bears on three continents and the black bear in America.
\BDescription:\b Bear Evolution
\BDrawing:\b Webster Publishing
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"Two Other Bear Species",4,naoy0445.bmp,b,017.wav
At least two other bear species, both very large, once roamed wide portions of North America. The Florida cave bear ranged from the Gulf Coast up into what is now Tennessee, and the short-faced bear was distributed from Alaska to Mexico and eastward across the continent to Virginia.
The latter was probably the largest of all the Ice Age bears, more than five feet (1.52 meters) high at the shoulder when walking normally -- not rising up on its hind legs -- and at least fifteen percent larger than today's Alaskan coastal grizzlies (a very big subspecies of brown bear). Grizzlies have been known to kill full-grown moose, and everything about the fossils of the short-faced bear indicates that it could easily kill the largest \Pprehistoric\p mammals.
\BDescription:\b Diagram of a bear skull.
\BDrawing:\b All Our Yesterdays
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"Today's Bears",5,faoy0334.bmp,c,018.wav
Most of the present forms of bears have probably been in existence for less than a million years. America's black bears evidently came from Asian \Pancestors\p and were well established long before grizzlies arrived in America. The earliest brown bears are thought to have originated in China. They spread through Asia and Europe and finally, during the Ice Age, crossed the Bering Strait land bridge to North America.
Youngest of the modern species is the polar bear, which evidently evolved from coastal Siberian brown bears -- according to some estimates only a hundred thousand years ago, and according to other estimates a little more than a quarter of a million years ago. Eventually, its numbers spread around the globe in \Parctic\p and \Psubarctic\p latitudes where vegetation is sparse or absent. Adapting to such harsh habitat, it not only acquired its white coat but also developed extremely specialized feeding habits, becoming the most truly \Pcarnivorous\p of the bear family. In many parts of its \Pcircumpolar range,\p a polar bear can live on seals alone.
\BDescription:\b 19th century engraving of a polar bear - the youngest of the modern species of bears.
\BDrawing:\b All Our Yesterdays
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"About Bears",6,will0001.bmp,c,019.wav
Although bears are members of the order \PCarnivora,\p they are not typical of the group. Most carnivores (with the exception of the seals, which are still placed by some authorities in a separate order Pinnipedia) are fast-running predators with long, narrow feet and are \Pdigitigrade,\p supporting themselves on their toes, which are sometimes reduced to four. Digitigrade locomotion, seen at an even greater level of development in horses, provides a third segment of the limbs and contributes to speed.
It is an ancient feature of the \PCarnivora,\p as is the fusion of many of the wrist and ankle bones, creating a hinge that works well in the fore-and-aft direction but gives little sideways mobility. Also associated with a running \Pgait,\p the \Pclavicle\p (collar bone) of carnivores is very reduced and does not, as in less specialized mammals, provide a girder between the \Psternum\p (breastbone) and scapula (shoulder blade) on which the forelimb can rotate. Typical carnivores have sacrificed this mobility in favor of speed.
Another general (almost diagnostic) feature of carnivores is a specialization of the fourth upper \Ppremolar\p and first lower molar of each side to form a shearing device that works like a pair of scissors to slice flesh. These are known as \Pcarnassial\p teeth and their action is readily observed when a cat or dog attacks a bone with the side of its mouth.
Although all bears can run moderately fast for short periods, they are by no means as swift as cats and dogs.
\BDescription:\b An illustration of digitigrade and plantigrade.
\BDrawing:\b Will Bourke
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"About Bears - (2)",7,01630100.bmp,b,020.wav
In addition to speed and agility, a successful predator must have acute senses of sight, hearing and smell, all of which are well developed in most of the \PCarnivora\p.
Although bears probably shared a common ancestor with the Canidae (dogs, wolves, foxes), they appear to have undergone a reversal of the evolutionary trends that characterize the \PCarnivora\p. This is not to say that they are "degenerate" but that they adopted a way of life that did not require the specializations mentioned above.
Although all bears can run moderately fast for short periods, they are by no means as swift as cats and dogs. Their feet are short and broad, with five toes, and their \Pgait\p is \Pplantigrade\p, weight being taken on the entire sole, from the toes to the heel. The sole is almost completely covered with hair in \Pterrestrial\p species, partly so in those that climb a lot. Associated with climbing and the need to rotate the forelimb, the \Pclavicle\p is better developed than in typical carnivores.
Fast-running carnivores have a long, flexible tail that contributes to balance when leaping, but the tail of bears is short as to be barely visible.
\BDescription:\b Bears can run fast over short distances.
\BPhoto:\b Todtri Productions Limited
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"About Bears - (3)",8,34690024.bmp,d,021.wav
However, a small genus, \ICephalogale,\i that lived about 25 million years ago and seems to have been close to the evolutionary origin of bears, had a tail as long as its head and body. Early bears, such as those of the genus \IUrsavus,\i which lived about twenty million years ago, had recognizably \Pcarnassial\p teeth but the course of evolution since then has seen a gradual bluntening of these. The other cheek teeth have also become broader, with rounded \Pcusps\p, adapted to crushing and grinding tough plant material such as leaves and nuts.
