Download Chapter 33: Mammals

Chapter 33: Mammals
Section 1: Mammals
Mammals

Includes many diverse species that vary greatly in appearance

Range in size from a _______________________ to a ____________________________

Mammals can be found flying in the air, running along the ground, and swimming in the
sea

Although
they
differ
in
size
and
habitats,
all
members
of
the
______________________________________ share certain characteristics
What Is a Mammal?

Mammals are endothermic animals, which means they are able to generate
substantial heat ____________________________

Most species are experts at maintaining a constant body temperature

Mammals use various combinations of _______________, ________________, and
___________________________________ to conserve body heat

Many mammals also have __________________________________ that help cool the
body

Sweat produced by sweat glands evaporates from the _______________, lowering body
temperature whenever necessary

With the exception of a few species, all mammals are ___________________________

This means that young mammals develop within the mother for a time and then are
__________________________

Female mammals have __________________________________, which produce milk to
nourish the young for some time after they are born

Mammary glands, which give mammals their name, are probably the most important
characteristic that scientists use to include an animal in class Mammalia

Mammals have several kinds of _____________________

Combined with their jaws, the teeth of mammals bite, chew, and grind food efficiently

Mammals have well-developed breathing muscles, including a ______________________

Mammals have a ________________________________________
Evolution of Mammals

The first mammals were __________________________

By the end of the Cretaceous Period, the mammals had split into three groups
o ____________________________

Only ________________ species survive today

Duckbill platypus
o ____________________________

Has a _______________ in which its young lives for a time

Kangaroo
o ______________________________________________


Mammals you are most familiar with

Mice, cats, whales, elephants, etc.
Because the fossil record is incomplete, it is hard to say precisely where and when each of
these three groups appeared
Form and Function in Mammals

Mammals have _____________________ and _________________________________
that have evolved many shapes to serve many functions in different environments
Feeding

Carnivorous mammals, such as cats and dogs, have strong, sharp teeth called
_________________________ and __________________________ that are used for
biting and ripping flesh from their prey

Carnivores use an __________________________________ chopping movement of their
jaws to chew their food

The behavioral and physical characteristics of many mammals allow them to capture prey

Herbivorous mammals, from cows to giraffes, eat plants that are tough and require
____________________________________________ in order to be digested

Herbivorous animals have evolved strong ________________ and flat edged incisors that
grasp and tear this tough vegetation

They chew by moving their jaws from __________________________________, using
flattened molars to grind the plant food into a pulp

Despite this efficient chewing, the _____________________________ that most plant
tissues contain is impossible for mammals to digest on their own

The vertebrate digestive system has never evolved the ability to produce enzymes that
digest cellulose

To help in the digestion of plant material, many grazing mammals have a chamber in their
digestive tract called the ____________________, in which newly swallowed plant food is
stored and processed for a time

The rumen contains thriving colonies of __________________________ that produce
enzymes needed to break down cellulose

After a certain amount of time, the mammal __________________________________ the
plant food from the rumen into its mouth

There the partially digested food is again chewed and mixed with saliva

_______________________________________

The 2nd time the food is swallowed, it moves through the rest of the digestive tract, where
digestion is completed and nutrients are absorbed

Some herbivores, such as rabbits, lack a rumen but have a large dead-end sac, or
_____________________, forming part of their intestines

Many of the same kinds of microorganisms that digest cellulose are found in the cecum

The ancestors of modern humans had a cecum, but over time it has shrunk to the small,
sometimes troublesome pouch we call the _________________________
Respiration

All mammals use _________________ powered by two sets of muscles

___________________________________ pull air in and push air out by moving the ribs
up and down to increase and decrease the size of the chest cavity

When the large muscles known as the ___________________________ contracts, it pulls
the bottom of the chest cavity downward, further increasing the cavity size and causing air
to rush into the lungs

Many mammals are able to use exhaled air to vibrate their vocal cords and produce a
variety of sounds, such as a ____________________, a _______________, or even a
_________________
Internal Transport

The mammalian circulatory system is an arrangement of ___________________________
____________________

The main pump, ______________________________, sends deoxygenated blood to the
lungs

After it leaves the lungs, the now oxygenated blood returns to the heart and is pumped
throughout the rest of the body via blood vessels

The two separate circuits – one to and from the lungs, the other to and from the rest of the
body – efficiently transports gases and nutrients to every cell of a mammal’s body
Excretion

Mammals have the most highly developed ________________________ of all vertebrates

Mammalian kidneys extract nitrogenous wastes from the blood in the form of
________________

Urea, water, and other wastes form _______________________

From the kidneys, urine flows to a urinary bladder, where it is stored until it is eliminated

The kidneys can also retain salts, sugars, and other compounds the body cannot afford to
lose
Response

Mammals have the most highly developed ________________________ of any animals

The brain consists of three parts: cerebrum, cerebellum, and medulla
o ______________________________: thinking, learning, understanding
o ______________________________: movement
o ______________________________: breathing, heart rate

Mammals depend on highly developed senses to provide themselves with information
about their environment

___________________ vary a great deal from one mammal species to another

With the exception of apes, monkeys, and humans, mammals do not see
___________________ well

All mammalian ears are built on the same basic plan, they also vary a great deal in their
abilities

The senses of smell and taste are often more highly developed in other mammals than in
humans

More than any other animal group, mammals depend on _________________________
___________________________ for protection
Movement

From the four limbs they inherited from their ancestors, mammals have evolved different
structures for movement

Running mammals can achieve great speeds on level ground

Climbing mammals have hands and feet with ____________________________________
that can grasp vines and branches

Flying mammals have arms modified to support flaps of skin that form
_____________________

Aquatic mammals have arms modified into _______________________________, which
they use to control their speed and direction in the water
Reproduction

The three groups of mammals differ greatly in their methods of reproduction

Egg-laying mammals, the ______________________________, are the most primitive
mammals and reproduce much like reptiles
o Oviparous
o Lays eggs that are incubated _________________________ the mothers body
o Once the young hatch, however, they nurse on __________________ provided by
the mother

Marsupials are _____________________________ and bear their young alive

The fertilized egg grows into an embryo inside the mother’s reproductive tract

The embryo is supplied with nourishment by a __________________________ on the egg

Because this yolk is not large enough to nourish the embryo through its entire
developmental
period,
the
embryo
must
leave
its
mothers
womb
_________________________________

At such an early age of development, the embryo is unable to survive alone

Instinctively,
it
crawls
across
its
________________________________
mother’s
fur
into
a
pouch
called
the

It spends the next several months there, growing sufficiently large and independent so that
it can leave the pouch

The early stages of placental embryos are much like those of marsupials

But in placental mammals, the embryo’s chorion, amnion, and allantois develop differently

Tissues from these membranes join with tissues from the mother’s uterus to form an organ
called the ___________________________

Nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and
mother through the placenta

The time the embryo spends inside the uterus is called the _________________________
___________________

The gestation period of mammals ranges from a few weeks in mice and rats to as long as
two years in elephants

The gestation period in humans is ___________________________________

After birth, most placental mammals provide their young with a period of care

The duration of parental care varies among different species

During the time infant and mother live together, the infant learns a great deal about its
surroundings from its mother

Many biologists believe that this long learning period is one of the most important benefits
of the prolonged childhood of many mammals