Mammals are characterized by having hair, a characteristic
as diagnostic as the feather of birds. Mammals generate heat internally,
and maintain a stable temperature (except species that hibernate or
go into short term torpor), and so are characterized as endothermic
homeotherms. Hair insulates mammals from heat loss in cool or cold
environments, but can also shield an animal from excess heat gain.
Mammals active metabolism is supported by an efficient respiratory
system that uses a sheet of muscle called the diaphragm to help
ventilate the lungs. The four-chambered heart of a mammal prevents
the mixing of oxygen-rich blood from the lungs with oxygen-poor
blood from the body, thereby maximizing the efficiency of the blood
flow and gas exchange.
Mammals as Learners
Mammals have larger brains than other vertebrates of equivalent
size, and seem to be the most capable learners. The duration of
parental care in many species extends the time for parents to teach
important skills to their young.
Reproduction
Mammary glands that produce milk are as distinctively mammalian
as hair. All mammalian mothers nourish their babies with milk, a
balanced diet rich in fats, sugars, proteins, minerals, and vitamins.
Most mammals bear their young live; only the platypus and echidna
of Australia lay eggs. Fertilization is internal, and the egg develops
into an embryo within the uterus of the female's reproductive tract.
In marsupials (pouched mammals), young develop only for a short
time in the uterus, and make their way to a pouch where they nurse
and grow. In placental mammals, the lining of the mother's uterus
and membranes arising from the embryo collectively form a placenta,
which transfers nutrients to the developing embryo. Baby placental
mammals live for an extended time in the uterus and are born in
a far more developed state than for non-placental mammals.
Teeth
Mammals also are know for having a variety of teeth. Whereas the
teeth of reptiles are generally conical and uniform in size, the
teeth of most mammal species are adapted for chewing many kinds
of foods. The teeth of a horse form large grinding surfaces for
chopping coarse grasses, whereas the teeth of cats and many other
carnivores are used for cutting meat and holding onto struggling
prey. Our own dentition, is a mixture of incisors modified for cutting,
and molars for grinding and crushing food.
Endangered Species
A species that is vulnerable in the Thompson-Okanagan region is
the Western Harvest Mouse (Reithrodontomys
megalotis), but even though vulnerable because of development
in the Okanagan, it is a fairly new species to the province and
may be moving in, rather than disappearing.
Another rare interior species is the Pallid
Bat (Antrozous pallidus). Scientists classify
bats in the Order Chiroptera, meaning "handwing". The
wings, thin double membranes of strong and elastic skin, stretch
across elongated fingers to the body and legs to provide excellent
maneuverability; bats are more maneuverable than many birds.
White-tailed Jackrabbit (Lepus
townsendii) is endangered and only rarely seen in the
Thompson-Okanagan region of southern British Columbia. There are
no confirmed breeding populations in British Columbia, and sightings
of this species are very rare. Jackrabbits are in the Order Lagomorpha,
an order that also includes: hares, pikas and rabbits.
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