Placental Mammals
Objectives
• Explain how placental mammals develop.
• Give an example of each type of placental
mammal.
I. Placental Mammals
• Mammals are divided into groups based on how
they develop.
A. A placental mammal is a mammal whose
embryos grow in an organ called a uterus. An
organ called the placenta attaches the embryo to
the uterus.
B. The length of time between fertilization and
birth is called the gestation period.
II. Anteaters, Armadillos, and Sloths
A. A few mammals have
unique backbones that
have special connections
between the vertebrae.
This group includes
anteaters, armadillos, and
sloths.
B. Most mammals in this
group eat insects they
catch with their long,
sticky tounges.
http://www.quantum-conservation.org/EEP/anteater.gif
http://t1.gstatic.com/images?q=tbn:ANd9GcRGw
DmlK_YYVOcvW1p41SaOzcMZlxpz8dOqSHm8tZiHZ
BJsHL61zDjBMOo5
III. Insectivores
A. Insectivores make up
another group of
mammals that eat insects.
This group includes
moles, shrews, and
hedgehogs.
B. Most members of this
group are small, have
long, pointed noses, small
brains, and simple teeth.
http://t1.gstatic.com/images?q=tbn:ANd9GcRAEpJ4G2CnQVx
F-Fjr93syeHRh5VpPW9pCnns3P0mRDz1rD79hGRRiBGGXcw
http://animal.discovery.com/tv/a-list/creaturecountdowns/hissy-fits/images/hissy-shrew.jpg
IV. Rodents
A. More than one-third of mammal
species are rodents. Rodents live on
every continent except Antarctica.
B. Squirrels, mice, rats, guinea pigs,
porcupines, and chinchillas are all
rodents.
C. Rodents have one set of incisors in
their upper jaw. Rodents gnaw and
chew so much that their teeth wear
down. But that doesn’t stop their
chewing––their incisors grow
continuously!
http://t3.gstatic.com/images?q=tbn:ANd9GcTJNyS_yEUb2x0bpKj6am1vOk1mgkxjGKEDvy8EWh-1BghmbrhsiXk5KuQEg
V. Rabbits, Hares, and Pikas
A. Rodents are similar to a group
of mammals that includes
rabbits, hares, and pikas. Like
rodents, they have sharp
gnawing teeth.
B. Unlike rodents, this group has
two sets of sharp incisors in their
upper jaw. Their tails are also
shorter than rodent’s tails.
http://wnpf.org/Upload/Images/pika2.jpg
Difference between rabbits and hares
VI. Flying Mammals
A. Bats are the only mammals that
fly. Bats are active at night. They
sleep in protected areas during the
day. Most bats eat insects or other
small animals. But some bats eat
fruit or plant nectar.
B. Most bats use echoes to find their
food and their way. Using echoes
to find things is called
echolocation.
http://animals.nationalgeogr
aphic.com/animals/mammal
s/common-vampire-bat/
Graphing Gestation Periods
Animal
Human Hamster
Dog
Cat
Pig
Horse
Blue
Whale
Elephant
Gestation
Period
(days)
270
61
63
114
336
360
660
16
VII. Carnivores
A. Mammals that have large canine
teeth and special molar teeth for
slicing meat are called carnivores.
B. Many mammals in this group eat
only meat, but other members of
this group are omnivores or
herbivores that eat plants.
C. Bears, cats, dogs, otters, raccoons
and pinnipeds––the group of fisheating ocean mammals that
includes seals, sea lions, and
walruses––are all carnivores.
http://www.firstpeople.us/pictures/bear/1600x1200/Feeling_Grizzly1600x1200.jpg
VIII. Trunk-Nosed Mammals
A. Elephants are the only
mammals that have a trunk.
The trunk is a combination of
an upper lip and a nose.
B. An elephant uses its trunk in
the same ways we use our
hands, lips, and nose. Elephants
use their trunks to put food in
their mouths and to spray
water on their backs to cool off.
http://t1.gstatic.com/images?q=tbn:ANd9GcRbLcYJ7Bl4WyscDgLdxe7errpfc42yl3tqFnmla1fdVKHGQqATjR
bk8Q1ig
IX. Hoofed Mammals
A. Horses, pigs, deer, and
rhinoceroses are some of the
many mammals that have thick
hoofs.
B. A hoof is a thick, hard pad that
covers a mammal’s toe. The
hoof is similar to a toenail or a
claw, but it covers the entire toe.
C. Hoofed mammals are divided
into two orders ––odd-toed and
even-toed––based on how many
toes are on each foot.
http://t2.gstatic.com/images?q=tbn:ANd9GcQgO
MnNUaHophfvQLTG8WvocSkS7DZ4cqZYpzO6qCm
xcxpiCTbiiSM-bRbI
X. Cetaceans
A. Cetaceans are a group of
mammals made up of whales,
dolphins, and porpoises. All
cetaceans live in the water.
B. While they may look like fish,
cetaceans have lungs and nurse
their young.
C. Like bats, cetaceans use
echolocation to find fish and
other animals.
http://www.dolphinworld.org/stories/porpoise.jp
eg
XI. Manatees and Dugongs
A. The smallest group of mammals that
live in the water are manatees and
dugongs. This group includes three
species of manatees and the dugong.
B. Manatees and dugongs use their front
flippers and a tail to swim slowly
through the water. They live along
coasts and rivers where they eat
seaweed and water plants.
C. Like cetaceans, manatees and
dugongs surface to breathe air.
http://t2.gstatic.com/images?q=tbn:ANd9GcSk
M4i4fAw66zQBerpqu1HqRzbAbIpvOo8GW0HND
WiZVrHK09UBf5LjHrBUWA
XII. Primates
A. Scientists classify prosimians, monkeys,
apes, and humans as primates.
B. These animals have five fingers on each
hand and five toes on each foot.
Primates have opposable thumbs, which
allow them to hold objects.
C. Primates have a larger brain than most
other mammals the same size have.
They are considered highly intelligent
animals.
Carnivore Conservation Debate
• Some carnivores are endangered due to habitat
loss, hunting, and poaching.
• One reason people kill these carnivores is
because they eat their livestock.
• Sometimes people kill them for their fur or body
parts.
• Should wolves be protected?
• What steps should be taken to support your
viewpoint?
• Write a paragraph stating your opinion.