Biology
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32-1 Introduction to the
Mammals
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32-1 Introduction to the Mammals
Mammals
What are the characteristics of mammals?
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32-1 Introduction to the Mammals
Mammals
All mammals have two notable features: hair and
mammary glands.
In females, mammary glands produce milk to
nourish the young.
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32-1 Introduction to the Mammals
Mammals
In addition to having hair and the ability
to nourish their young with milk, all
mammals
• breathe air.
• have four-chambered hearts.
• are endotherms that generate their
body heat internally.
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32-1 Introduction to the Mammals
Evolution of Mammals
When did mammals evolve?
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32-1 Introduction to the Mammals
Evolution of Mammals
Evolution of Mammals
Mammalian fossils are characterized by a lower
jaw with a large, teeth-bearing bone connected
directly to the skull by a joint, and distinctive
features of the limbs and the backbone.
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32-1 Introduction to the Mammals
Evolution of Mammals
Mammals are descended from ancient reptiles.
Ancestors of modern mammals diverged from ancient
reptiles during the Carboniferous Period.
For millions of years, various mammal-like reptiles
lived alongside other reptile groups.
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32-1 Introduction to the Mammals
Evolution of Mammals
The first true mammals appeared during
the late Triassic Period, about 220 million
years ago.
These mammals were very small and
probably nocturnal.
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32-1 Introduction to the Mammals
Evolution of Mammals
After the extinction of dinosaurs, mammals
underwent an adaptive radiation.
They increased in size and occupied many new
niches.
The Cenozoic Era is called the Age of Mammals.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Form and Function in Mammals
The mammalian body has adapted in varied ways
to a great many habitats.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Body Temperature Control
Mammals are endotherms.
A high rate of metabolism helps mammals
generate body heat.
Mammals have external body hair that helps them
keep warm.
Subcutaneous fat, which is a layer of fat located
beneath the skin, also helps conserve body heat.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Many mammals have sweat glands that help cool the
body.
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If its body temperature gets too high, the
mammal sweats.
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Evaporation of sweat then cools the body.
•
Some mammals pant to cool down.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
How do mammals maintain homeostasis?
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The ability of mammals to regulate their
body heat from within is an example of
homeostasis.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Feeding
Because of its high metabolic rate, a mammal
must eat a lot of food to maintain homeostasis.
Some mammals are herbivores. Some mammals
are carnivores. Some mammals, including
humans, are omnivores.
Certain whales are filter feeders.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
As mammals evolved, the form and function of
their jaws and teeth became adapted to eat foods
other than insects.
The joint between the skull and lower jaw allowed
mammals to evolve larger, more powerful jaw
muscles and different ways of chewing.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Jaws and Teeth of Mammals
Carnivore
Herbivore
Canines
Jaw
joint
Wolf
Incisors
Molars and premolars
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Jaw
joint
Horse
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Canines: Canines are pointed teeth. Carnivores use
them for piercing, gripping, and tearing. In herbivores,
they are reduced or absent.
Canines
Wolf
Horse
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Incisors: Chisel-like incisors are used for cutting,
gnawing, and grooming.
Wolf
Incisors
Horse
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Molars crush and grind food. The ridged shape of the
wolf’s molars and premolars allows them to interlock
during chewing, like the blades of scissors. The
broad, flattened molars and premolars of horses are
adapted for grinding tough plants.
Wolf
Molars and premolars
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Horse
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32-1 Introduction to the Mammals
Form and Function in
Mammals
A mammal’s digestive tract breaks down and absorbs
the type of food that it eats.
Carnivores have a short intestine because enzymes
quickly digest meat.
Herbivores have a longer intestine because tough,
fibrous plant tissues take longer to digest.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Cows have a stomach chamber called the rumen, in
which swallowed plant food is stored and processed.
It contains bacteria that digest the cellulose of plant
tissues.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Respiration
All mammals use lungs to breathe.
A diaphragm is a large, flat muscle at the bottom
of a mammal’s chest cavity that helps in breathing.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
When an animal inhales, chest muscles lift the rib
cage up and out. The diaphragm pulls the chest
cavity down.
The combined actions of the chest muscles and
diaphragm increase the volume of the chest cavity.
The increase in volume pulls air into the lungs.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
When an animal exhales, chest muscles lower the rib
cage. The diaphragm relaxes, and the volume of the
chest cavity decreases.
Air is then pushed out of the lungs.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Circulation
The mammalian circulatory system has two loops
and a four-chambered heart.
The right side of the heart receives oxygen-poor
blood from the body and pumps it to the lungs.
The left side receives oxygen-rich blood from the
lungs and pumps it to the rest of the body.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Mammalian
heart
Left atrium
Right atrium
Left ventricle
Right ventricle
Complete
division
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Excretion
Kidneys extract nitrogenous wastes from the blood
in the form of urea.
Urea, other wastes, and water combine to form
urine.
From the kidneys, urine flows to a urinary bladder,
where it is stored until it is eliminated.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The kidneys of mammals help maintain
homeostasis by filtering urea from the
blood, as well as by excreting excess water
or retaining needed water.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The kidneys control the amount of water in the body.
This enables mammals to live in many habitats in
which they could not otherwise survive.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Response
Mammals have well-developed brains with three
main parts:
• cerebrum—controls thinking and learning
• cerebellum—controls muscular coordination
• medulla oblongata—regulates involuntary body
functions
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Mammalian
Brain
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The cerebrum has a well-developed outer layer
called the cerebral cortex, which is the center of
thinking and other complex behaviors.
Some behaviors, such as reading, are possible only
with the human cerebral cortex.
Mammals other than humans also exhibit complex
behaviors.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Mammals rely on highly developed senses to detect
and respond to stimuli from their external
environment.
Many have well-developed senses of smell and
hearing.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
All mammalian ears have the same basic parts, but
they differ in their ability to detect sound.
•
Dogs, bats, and dolphins detect sounds at
higher frequencies than humans can.
•
Elephants detect sounds at much lower
frequencies.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The ability to distinguish colors varies among
species.
Color vision is most useful to animals that are active
during the day.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Chemical Controls
Mammals have endocrine glands that regulate
body activities by releasing hormones.
Hormones are substances produced in one part of
an organism that affect another part of the same
organism.
Hormones are carried by the blood to the organs
that they affect.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Fighting Disease
The immune system helps protect animals from
disease.
Barriers, such as the skin, prevent pathogens from
entering the body.
Specialized cells and chemicals recognize and
destroy pathogens.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Movement
Mammals have backbones that flex vertically and
side to side.
Shoulder and pelvic girdles are streamlined and
flexible, permitting both front and hind limbs to
move in many ways.
Variations in limb bones and muscles permit a
variety of movements.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
The limbs and digits (fingers and toes) of many
mammals are adapted to their particular way of life.
Note the variety of lengths and shapes of the limb
bones. Homologous bones are the same color in all
the drawings.
Monkey
Horse
Mole
Bat
Seal
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Reproduction
Mammals reproduce by internal fertilization.
The male deposits sperm inside the reproductive
tract of the female, where fertilization occurs.
All newborn mammals feed on their mother’s milk.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Young mammals need care from one or both parents
when they are born and for a long time afterward.
Parental care ensures that young will survive and
reproduce.
The duration and intensity of parental care varies
among different species.
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32-1 Introduction to the Mammals
Form and Function in
Mammals
Some mammal species, such as lions, live in groups
in which the young may be cared for by adults other
than the parents.
Group living provides young mammals with complex
social interaction among adults and juveniles.
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32-1
Click to Launch:
Continue to:
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32-1
One characteristic commonly used to determine
whether fossils are mammals is
a. subcutaneous fat.
b. mammary glands.
c. a jaw joint that allows movement from side to
side.
d. hair or fur.
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32-1
How many chambers do mammalian hearts
have?
a. 2
b. 3
c. 4
d. 6
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32-1
Mammals are called endotherms because they
a. produce milk to nourish their young.
b. have well-developed sense organs.
c. have powerful jaws and specialized teeth.
d. generate their body heat internally.
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32-1
The first true mammals appeared in the fossil
record
a. soon after the extinction of the dinosaurs.
b. about the same time as the first reptiles.
c. during the Triassic when dinosaurs were the
dominant land animals.
d. long after the extinction of the dinosaurs.
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32-1
The duration of parental care in mammals
a. varies among different species.
b. is one to four weeks.
c. is six months to a year.
d. is intermediate compared to reptiles.
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