Mammals share 7 key characteristics: (1) making milk, (2) breathing air, (3) being endothermic, (4) having hair, (5) having specialized teeth, (6) sexual reproduction, and (7) having large brains. Placental mammals make up the majority of mammals and their embryos develop inside the mother's uterus, receiving nutrients via the placenta. Living placental mammals are divided into 11 main groups including insectivores, rodents, carnivores, hoofed mammals, primates, and cetaceans.

1. Characteristics of
Mammals

2. The First Mammals
• 280 million years ago, reptiles called
“therapsids” existed, which had
characteristics of both reptiles and
mammals
• True mammals appeared soon after
• They were about the size of mice, were
warm blooded, and were able to hunt at
night because they could maintain their
body temperature

3. Common Characteristics
• Mammals share 7
characteristics:
– 1) Making Milk
• All mammals have
mammary glands, which
are structures that make
milk
• Only mature females
produce milk for their
young
• All milk is made of
sugars, water, proteins,
and fats

4. – (2) Breathing Air
• Mammals use
their lungs to get
oxygen from the
air
• Mammals have a
muscle to help
them get air
called a
diaphragm it
lies at the bottom
of the rib cage

5. – (3) Endothermic
• As oxygen helps
break down a
mammal’s food,
energy is released
• This energy keeps
a mammal warm
• Like birds,
mammals are
endotherms
• Helps them survive
in cold areas

6. – (4) Hair
• Mammals stay
warm by having
hair
• Thick coats are
called fur
• Most mammals
have a layer of
fat under their
skin to keep
them warm
• This fat traps
heat in the body

7. – (5) Specialized Teeth
• Mammals have teeth
with different shapes
and sizes for
different jobs
• Meat-eating
mammals have large
canines to help eat
prey
• Plant-eating
mammals have
larger incisors and
molars to help them
bite and grind plants

8. – (6) Sexual
Reproduction
• Most mammals
give birth to live
young
• Newborn
mammals stay
with at least one
parent until they
are grown

9. – (7) Large Brains
• Mammal’s brain is
much larger than that
of most other animals
of the same size
• Allows mammals to
learn and think
quickly
• Also allows mammals
to respond quickly to
events around them
• Mammal uses its
senses to find out
about the world

10. Placental Mammals
• Placental mammal: embryo develops
inside the mother’s body in an organ
called a uterus
– The placenta attaches the embryo to the
uterus
– Placenta carries food and oxygen from the
mother’s blood to the embryo and carries
wastes away from the embryo
– The time that the embryo develops is called
the gestation period

12. • Living placental mammals
are divided into 11 main
groups that contain 18
orders:
– (1) anteaters,
armadillos, & sloths
• These mammals are
called “toothless
mammals” but only
anteaters have no
teeth
• Most catch insects
with long, sticky
tongues

13. • Insectivores • Rodents
– Eat insects – More than one-third of
– Most are small with mammal species are
long pointed noses rodents
– Include moles, shrews, – Include squirrels,
and hedgehogs mice, porcupines

14. • Rabbits, Hares, and • Flying Mammals
Pikas – Bats are the only
– Have sharp, gnawing mammals that fly
teeth – Most use echoes to
– Have 2 sets of incisors find their food and they
in their upper jaw way
– Shorter tails than
rodents

15. • Carnivores • Trunk-Nosed
– Have large canine Mammals
teeth and special – Elephants are the only
molar teeth for slicing living mammals with a
meat trunk
– Many only eat meat – A trunk is a
– Includes bears, cats, combination of an
dogs, otters, hyenas upper lip and nose

16. • Hoofed Mammals • Cetaceans
– A hoof is a thick, hard – All cetaceans live in
pad that covers a the water
mammal’s toe – Unlike fish, they have
– Most hoofed mammals lungs and nurse their
are fast runners young
– Includes giraffes, – Includes whales,
camels, pigs dolphins, and
porpoises

17. • Manatees and • Primates
Dugongs – Have 5 fingers on
– Smallest group of each hand and 5 toes
mammals that live in on each foot
the water – Considered highly
– Used their front intelligent animals
flippers and tail to – Includes monkeys,
swim slowly apes, and humans

18. • Monotremes
– Mammals that lay
eggs
– Examples: duck-billed
platypus, echidna
• Marsupials
– Mammals that carry
their young in a pouch
– Several species of
marsupials living today
– Examples: koalas,
opposum, kangaroo