Facts about the beginnings of the bear are
quite undetermined. Apparently, about 30 to 40 million years ago,
during the early portion of the Oligocene epoch, bears began to evolve
from a family of small, carnivorous, tree climbing mammals called miacids.
Coyotes, wolves, foxes, raccoons, and dogs are also thought to have evolved
from this ancestral stock. Very early in the history of the
miacids developed special teeth for piercing and tearing flesh the canine
teeth. The early carnivores developed other special teeth called
carnassials. The last premolar I the upper jaw and the first molar
in the lower jaw were modified to ac like scissors, shearing meat into
easily swallowed chunks. At first, the brains of these carnivores were small, perhaps
because those early herbivores on which they fed could caught without much
trouble. Meat eating became a highly successful occupation for carnivores,
and they quickly radiated into three main branches: the dog, the cat, and
seal families. The first true bears evolved from the tribe of heavy
bear like dogs that existed in North America during the late Oligocene
epoch, some 27 million years ago. According to some researchers, the oldest known bear, Ursavus
elemensis, was about the size of a fox terrier. It lived about 20
million years ago in a subtropical Europe. Bears came into their
own about 6 million years ago and quickly evolved into numerous forms.
Some grew to enormous size. Then, because of widespread changes,
probably climatic, nine genera and numerous bear species became extinct.
Somewhere during this time our modern line of bears developed from a little
bear known as Protursus , which also died out in time.
Rise and Downfall of the Third Bear
About 2.5 million years ago the first of the genus Ursus (Latin
for bear) appeared. From its European descendants came the Etruscan
bear, Ursus etruscus, which later separated into three distinct lines.
Two of these lines were found in Asia, and is thought that they lead to
today's brown bears and black bears. The third line, now extinct,
lived in Europe, and is known as the cave bear, ursus spelaus. Cave
bears were contemporaries of early humans, who probably hunted them for
food. Fossil remains of cave bears span the period from 30,000 or
40,000 (maybe even 50,000) years to about 10,000 years ago. Just why the cave bear died out is a subject of great speculation
among paleontologists. Some assert that the bar perished of its own
"self domestication" from prolonged internment during the long Ice Age
winters. When large predators are kept for many years in the confinement
of cages, peculiar diseases of the spinal column develop. These include
inflammations, fusing, and atrophy. An extraordinary large number
of cave bears remains are from the diseased or physically degenerated bears. Also extraordinary are the numbers of cave bear skeletons
that have been discovered. The most impressive find was in dragon's
cave at Mixnitz in Austria. Here the skeletal remains of over 30,000
animals were piled up. How did they all get in there ? No one
really knows . A stone chest filled with bear skulls, uncovered in
Drachenloch Cave in the Swiss Alps, suggests the possibility that the cave
bear may have been on e of man's first hunting trophies. In a cave
near Erd, Hungary lie the bones of more than 500 cave bears that
were supposedly killed by Neanderthal man. Dating by carbon
14 methods indicates that the bones remains whose demise seems to have
been linked to humans. Did early Europeans cause, or at least hasten,
the extinction of the cave bars/ Its probable. Many cave bear skeletons
still retain traces of ax blows. Whatever the reasons for its demise, the cave bears is long
gone. The European brown bear, which took
its place, is only a third the size of its Ice Age ancestors.
If a bear is removed from its home range it will display an extraordinary
homing instinct. In Michigan, an adult male black bear homed
after being transplanted by air for a distance of 156 miles (251 km).
Twelve adult Alaskan brown bears returned to their capture sites
in an average of fifty-eight days. They all had been transplanted
over 125 miles (201 km) away.
A bear’s instinct to den is an adaptation to life in places where
winter conditions might otherwise threaten survival. For some unknown
reason, a few individuals of a hibernating species may remain active all
winter even though no food maybe available. Normally, the problems
of reduced food supply, decreased mobility because of deep snow, and the
increased energy costs of keeping warm are solved by denning and hibernation. Northern bears usually choose a low cave, a hollow
tree, or the shelter of a brush pile as a den site in which to hibernate.
Sometimes an earthen den is dug directly into the ground. Often the
den chamber is lined with dried grasses and leaves to make an insulated
bed. Denning time generally coincides with the first inclement
winter weather, although the disappearance of high-quality food determines
the actual time of denning. During late summer, bears have
been known to eat as much as 20,000 calories a day in a final effort to
accumulate enough fat reserves for hibernation. This is equivalent
to a human eating thirty-eight banana splits or forty-two hamburgers a
day. Most zoo bears, when regularly fed throughout winter, do not
den. During the last days before hibernation, some kinds
of bears will eat certain indigestible materials—resinous plants and fibers—which
form a mass in the rectum and plug the anus. The function of the
anal plug is not well understood. Biologists differ as to whether or not bears enter
a state of true hibernation, but the controversy may be largely a matter
of terminology. Many smaller mammals, such as chipmunks and marmots,
enter a deep sleep from which they cannot be easily aroused. While
they are dormant, their body temperature are considerably lower than normal.
A hibernating bear’s temperatures are considerably lower than normal.
A hibernating bear’s temperature, in contrast, does not drop more than
about 9 F 95 C) from its normal 87.8 to 99 F (31 to 37.4 C). Bears
can be easily awakened, but if undisturbed, they may sleep for as long
as a month without changing position. Hibernating bears can remain in their dens from two and a
half to seven months, depending on climate, without eating food, drinking
water, urinating, or defecating. Smaller mammals, however, must wake
up periodically to eat and expel body wastes. Bears accomplish this amazing fast through their unique
metabolic system. During hibernation the water content of their blood
remains at a constant level. Minor losses of water are balanced by
the breakdown of fat reserves. Although a small amount of urea is
continually formed, it is quickly degraded by a refined system that recycles nitrogen and prevent toxic uremia.
Knowledge about these metabolic system is helping researchers to develop
special diets for humans with kidney problems and diabetes. During winter hibernation a bear burns about 4,000
calories a day. Although its heart rate drops to about eight bears
per minute, compared to from forty to fifty beats per minute during summer
sleep, its oxygen consumption rate may drop only about 50 percent of that
of an active bear. Bears also have been known to shiver in order
to generate enough heat to keep warm during hibernation. When bears leave their dens in the springtime, it may
take weeks before they resume their normal intake of ood. Apparently,
these metabolic adjustments of hibernation persist for some time after
they have become active again.
The world’s most recently evolved bear, the polar bear,
is thought to have branched off the European ursus stock of brown bears
about 100,000 years ago. Every continent except Australia has had or still
has bears. Today only eight species survive. In some places
their numbers have become so greatly reduced that forms of six species
are now included in the International Union for the Conservation
of Nature (IUCN) red-list of endangered animals.
Body of the Bear
As a group, bears all look pretty much alike, varying in size
and color but not in general shape. A comparison of skeletons reveals many
similarities to dogs and wolves. But unlike members of the dog family,
bears grow to be quite large, more than 100 pounds (45kg) as adults.
Some reach massive sizes. Bears have heavily built bodies with relatively short legs,
necks, and tails. They have large heads with rounded ears and usually small eyes for
so large an animal. Unlike other carnivores, a bear’s lip are free
from the gums, allowing them to be mobile and protrusible. Their
heavy pelts, padded by several inches of fat, often create the illusion
of a slow and clumsy animal. This is not so—a big brown bear can
reach a speed of 35 or 40 mph (56 or 64 kmph.) for crashing blow
from a forepaw. Most bears are unable to leap even a few feet off the
ground. Nearly all are expert climbers, however, and all bears are
capable of swimmers.
The five toes of each broad foot are equipped with curving, non-retractable
claws. The claws are usually longer on the hind feet than on the
front feet. In spite of having claws instead of fingers, bears are
very adept at manipulating objects with their front feet. I have
seen a big brown bear delicately turning a feather over and over in its
paws. The forepaws make useful digging instruments which are constantly
employed as the bear forages for food. Like humans, bears are plantigrade;
they put their heel and foot down flat on the ground when they walk.
This flat-footed stance makes it easy for them to stand up on their hind
legs. When walking on all fours, bears turn their front feet inward
in a pigeon-toed position.
Teeth and Birthdays
Bear’s teeth, though large are not particularly specialized
for meat eating. They have pointed canines that help catch kill prey,
but their premolars (carnassials) are no longer specialized for tearing
meat. Their molars are the heavy, crushing type of typical of plant
eaters. 9More than 75% of most bears diet consist of plant material.) Wild bears may live more than thirty years. But a very
old bear is unusual because of the heavy toll caused by hunting and other
mortality factors. Sometimes an entire bear population may be younger
than ten years of age. Generally speaking, a young population indicates
a high deah rate among bears. Varying widths of annuli in the teeth indicate the
history of the animals general health. In a female’s teeth, for example,
if the annuli are very close together, usually indicates that she had cubs
and was lactating at the time the rings were formed.
Northern bears have a terrific motivation to gain weight.
Since much of their year is spent asleep in hibernation, they have only
a short active period in which to find enough food to survive the winter.
Much of a bear’s waking time is spent solving the problem of getting food,
the more nutritious the better. For example, bear’s prefer to eat
plants when they are at the peak of protein content -usually during pre-flowering
or early flowering stages. If food becomes extremely abundant, such as during
salmon run in Alaska, bears may become selective about what portions of
the fish they eat. Hungry bears will eat the entire salmon.
They prefer, however, to eat the eggs of the female salmon, which
are extremely rich in nutrition. When a bear catches a salmon
it determines at once whether it is a male o a female. If a salmon
are plentiful, the bear will often abandon the males and resume fishing
in hope of catching a female salmon. A bear normally spends its time in a series of small
areas where it can find food. Collectively, these areas make up its
home range. It moves around within this range in order to take advantage
of seasonal food sources. The routes to and from these area of use
are often called lanes. Although bears will use human roads, 95 percen
of their travel is off-road, particularly in swamps and forests.