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Fundamentals of Biology
Lesson 25
Mammals
I. General Characteristics.
A. Hair.
B. 4-chambered heart.
C. Diaphragm.
D. Endothermic.
E. Internal fertilization.
F. Most are viviparous.
G. Most have a placenta.
H. Nurse young.
I. Pronounced cerebrum.
II. Hair.
A. Nonliving cells produced by hair follicles deep in the
skin.
B. Types.
1. Underhair: insulates.
2. Guard hair: provides color.
C. Functions.
1. Insulation: e.g. beaver.
2. Camouflage: e.g. snowshoe hair.
3. Sensory.
a. Whiskers
of cats and dogs.
b. Back of a
dog’s neck.
4. Protection: e.g. porcupine.
III. Limbs.
A. 2 pairs, used for locomotion.
B. Provisions for rapid movement.
1. Narrow foot track – legs much
further under the body than in reptiles.
2. Limb girdles (Part of the pectoral
girdle of the cat moves back and forth several inches with each leg movement,
lengthening the stride).
3. Muscles clustered at top of the
leg, making the lower leg slim and light.
4. Cheetah can go 60 mph.
C. Variations.
1. Bat: membrane connects the fingers
making a wing.
2. Mole: short, stout forelimbs serve
as shovels.
3. Whale: forelimbs are massive
paddles.
4. Kangaroo: muscular hind legs
enable it to jump almost 40 ft.
IV. Digestion.
A. Types of teeth.
1. Incisors.
a. Flat,
thin, in front of mouth.
b. Used for
biting.
2. Canines.
a. Round,
pointed, toward front of mouth.
b. Used for
tearing.
3. Molars.
a. Thick,
short teeth in rear of mouth.
b. Used for
grinding and chewing.
B. Cellulose-eaters.
1. Vertebrates cannot digest
cellulose.
2. Forage first goes to the rumen
where bacteria produce cellulose-digesting enzymes.
3. Ruminants periodically regurgitate
partially digested food (cud) to chew it more thoroughly.
4. Food eventually makes it way into
the true stomach.
V. Temperature control.
A. Cold weather.
1. Small extremities.
2. Compact body.
3. Heavy coat of fur.
4. Hibernation.
B. Hot weather.
1. Sweating: skin.
2. Panting: tongue and mouth.
3. Large ears.
4. Bathing.
VI. Reproduction.
A. Ovaries produce ova.
B. The ova pass through the oviduct toward the uterus.
C. The ova are fertilized while in the oviduct.
1. This period is called “heat”.
2. The female releases odors which
attract males.
D. Internal fertilization.
E. Cell division and beginning of the embryo.
F. Implantation in the uterine wall.
G. A placenta forms: an organ that transfers nutrients from
the mother to the embryo.
H. Gestation.
1. The period of pregnancy.
2. Can run from 21 days (mice) to 335
days (horse).
I. After birth, mothers nurse the young with milk from their
mammary glands.
VII. Three groups.
A. Monotremes.
B. Marsupials.
C. Placentals.
VIII. Monotremes.
A. Three species.
1. Duck-billed platypus (Australia).
2. Two kinds of spiny anteaters
(Australia, New Guinea).
B. Lay eggs.
1. Similar to reptile eggs.
2. Lay them in burrows in the ground.
3. Incubate them with their bodies.
C. Nurse the young.
1. Do not have nipples.
2. Milk spills onto the skin and the
young lap it off.
D. Platypus.
1. Broad, flat tail used in swimming.
2. Digs for invertebrates in the mud
with its bill.
3. Webbed, clawed feet.
4. Produces poison at its hind legs.
IX. Marsupials.
A. Pouched mammals (marsupium - pouch)
B. Found only in Australia and America, but there are
fossils in Europe.
C. Reproduction.
1. Have no placenta.
2. Eggs are yolky.
3. Embryo feeds on the yolk and
uterine fluid.
4. May be born as soon as 8 days
after fertilization.
5. Crawl out of the uterus to the
mothers pouch.
6. Clamp onto a nipple.
7. Mother pumps milk into the baby
while it completes development.
D. Types.
1. Kangaroo.
2. Koala.
3. Wallaby: like a small kangaroo.
4. Wombat: rodent-like.
5. Phalanger: like a squirrel.
6. Tasmanian devil: like a raccoon.
7. Tasmanian wolf: like a dog.
8. Oppossum.
X. Placentals.
A. Rodents.
1. The largest mammalian order.
2. Includes squirrels, rats, mice,
gophers, porcupines.
3. Have large, chisel-like incisors
in upper and lower jaws.
a. Grow
throughout life.
b. The rodent
must gnaw constantly to keep the incisors from growing too long.
4. Frequent prey for reptiles, birds,
and other mammals.
5. Avoid extinction by rapid
reproduction.
a. Meadow
mice can produce up to 17 litters, 75 babies per year.
b. Young
field mice are independent at 4 weeks, reproducing at 6 weeks.
B. Carnivores.
1. Enlarged canine teeth (fangs) and
sharp molars for tearing prey.
2. Limber, powerful limbs.
3. Sharp claws.
4. Able to learn and hunt
intelligently.
5. Families.
a. Cat: hunt
by stealth.
b. Bear
(actually omnivorous): capture prey by strength.
c. Dog: hunt
with endurance and teamwork.
d. Seals,
walruses, sea lions.
e. Raccoons,
mink, otters, weasels, badgers, wolverines.
C. Aquatic.
1. Whales, dolphins, porpoises.
2. Never come ashore.
3. Limbs are flippers.
4. Tails are horizontal flaps.
5. Must surface to breathe.
6. Some have nostrils on top of their
heads.
7. Blue whale is the largest living
animal.
a. Can reach
109 ft., weigh 170 t.
b. Feeds on
plankton using baleen.
8. Dolphins and porpoises are among
the most intelligent animals.
a. Seem to
communicate underwater.
b. Easily
trained.
D. Primates.
1. Stand erect.
2. Freely moving arms and legs.
3. Opposable thumbs and toes.
4. Nails on most fingers and toes.
5. Binocular vision.
6. Poor sense of smell.
7. Most are normally tree-dwellers.
8. Less specialized teeth.
9. Mostly vegetarian.
10. Chimpanzees.
a. May be the
smartest animals.
b. Use tools
in the wild.
c. Can be
trained to communicate.
E. Hoofed.
1. Toes are enlarged and hardened.
2. Grazing animals.
3. Odd-toed.
a. Either 1
hoof or 3 enlarged toes.
b. Simple
stomachs.
c. Horses,
asses, zebras, rhinoceroses.
4. Even-toed.
a. 2 or 4
functional hoofed toes.
b. Long legs.
c. Many have
antlers or horns.
d. Simple
stomach group: pigs, hippopotamuses.
e. Ruminants:
cattle, deer, camels, giraffes, antelopes, buffalo, goats, sheep.
F. Misc.
1. Toothless: armadillo.
2. Flying: bat.
3. Trunked: elephant.
4. Rodent-like: rabbit.
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