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

oOviparous

oLays eggs that are incubated ______the mothers body

oOnce 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