- Possess hair which is made of keratin.
The evolution of mammalian keratin is believed to be independent of
reptilian keratin. Hair provides insulation .
- Endothermic. The majority of the heat
energy is used to maintain their high body temperature.
- 4 chambered heart.
- Mammary glands are used to
produce milk to nourish their young. Female glands are the only
functional glands.
- The diaphragm is a muscle that
separates the thoracic cavity from the abdominal cavity.
- 7 cervical vertebrae (neck bones) are
present in most mammals.
- Most are viviparous though some are
oviparous. An extended gestation period (uterine development)
is common in most placental mammals.
- Teeth are imbedded in the jaw bone and
come in a variety of forms.
- Well developed brain.
- Mammals developed from the therapsid
ancestors during the Triassic period.
Major Groups of Mammals:
- Monotremes. Characterized by the
duckbilled platypus and the spiny anteaters, lay eggs and maintain
some reptilian characteristics. They do not contain true mammary
glands, but produce a fatty sweat (milk) from glands in the skin. The
milk collects and drips down tufts of hair into the offspring's mouth.
They are found in Australia and New Guinea.
- Marsupials. These mammals contain
a pouch (marsupium). Opossums,koalas,kangaroos, and other
examples live in Australia as a result of the break up of the super
continent Pangea. The young are born during the early stages of
development. The new born crawls up to the mother's pouch, where it
clings on to a nipple and hangs there until it fully develops.
- Placental Mammals. These mammals
are the most abundant and diverse of the class. The placenta, a
reproductive structure, is housed in the uterus of the female. Here
the offspring receives all that it needs to develop into a fully
developed organism. This period of development (gestation) varies with
the species of mammal. Whales gestate for 2 years, while a mouse
develops in 21 days.
Chart of Placental Mammals
| Order |
Characteristics |
Examples |
| Carnivora |
Eats meat, all teeth are pointed |
cats and dogs , seals, walrus,
weasels, and martins |
| Chiroptera |
wings used for flight, diet
includes insects and vegetation
|
bats |
| Primates |
opposable thumb, plantigrade foot,
usually one offspring at birth.
|
man , apes, monkeys,tarsiers,and
lemurs |
| Edentata |
lacking teeth, large claws for
digging |
sloths, armadillos, South American
anteater |
| Rodentia |
2 incisors on both jaws, diastema
between incisors and premolars |
rats, mice, squirrels, beavers,
gophers, and capybara |
| Lagmorpha |
4 incisor teeth, canine teeth
lacking, short stubby tails |
rabbits, hares,pikas |
| Cetacea |
flippers, opening on top of head |
dolphins,whales,porpoises |
| Proboscidea |
Great size,nose and upper lip form
proboscis, upper incisors are tusks,thick skin,scant hair |
elephant |
| Sirenia |
Herbivorous, aquatic, no external
ears, flippers, no hind appendages |
Manatees and dugongs |
| Perissodactyla |
Odd-toed,hoofed forms,gall bladder
lacking, herbivorous |
horses, donkeys,zebras,tapirs |
| Artiodactyla |
Even-toed, hoofed forms,
herbivorous, true horns or antlers present |
Cattle,pigs,camels,deer,hippopotami |
|