Transcript Chapter 33: Mammals - Elida Local Schools

Chapter 33: Mammals
Section 1: Mammals
Mammals
Includes many diverse species that vary
greatly in appearance
Range in size from a tiny mouse to a huge
elephant
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 class Mammalia share
certain characteristics
What Is a Mammal?
Mammals are endothermic animals, which
means they are able to generate
substantial heat internally
Most species are experts at maintaining a
constant body temperature
Mammals use various combinations of fur, hair,
and subcutaneous fat to conserve body heat
Many mammals also have sweat glands that help
cool the body
Sweat produced by sweat glands evaporates
from the skin, lowering body temperature
whenever necessary
What Is a Mammal?
With the exception of a few species, all mammals
are viviparous
This means that young mammals develop within
the mother for a time and then are born alive
Female mammals have mammary glands,
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
What Is a Mammal?
Mammals have several kinds of teeth
Combined with their jaws, the teeth of
mammals bite, chew, and grind food
efficiently
Mammals have well-developed breathing
muscles, including a diaphragm
Mammals have a four-chambered heart
One characteristic that unites all
mammals is hair. This brown bear and
her cubs can sleep through winter’s cold
insulated by their thick coats and a layer
of fat beneath their skin.
Be they lions or whales, all
mammals breathe air. Breathing
is easy for land mammals, but
sea mammals must return to the
surface to breathe.
All female mammals nurse
their young, feeding them
milk they produce in
mammary glands. These
glands are the source of the
class Mammalia’s name.
Evolution of Mammals
The first mammals were very small
By the end of the Cretaceous Period, the mammals had split
into three groups
 Monotremes
 Only three species survive today
 Duckbill platypus
 Marsupials
 Has a pouch in which its young lives for a time
 Kangaroo
 Placental mammals
 Mammals you are most familiar with
 Mice, cats, whales, elephants, etc.
Evolution of Mammals
Because the fossil record is incomplete,
it is hard to say precisely where and
when each of these three groups
appeared
The fossil record shows that the first
mammals resembled this tree shrew. Tree
shrews are omnivores; they eat both plants
and animals.
Form and Function in
Mammals
Mammals have limbs and organ
systems 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 incisors
and canines that are used for biting and
ripping flesh from their prey
Carnivores use an up and down chopping
movement of their jaws to chew their food
The behavioral and physical characteristics of
many mammals allow them to capture prey
Feeding
Herbivorous mammals, from cows to giraffes,
eat plants that are tough and require
thorough chewing in order to be digested
Herbivorous animals have evolved strong lips
and flat edged incisors that grasp and tear
this tough vegetation
They chew by moving their jaws from side to
side, using flattened molars to grind the plant
food into a pulp
Feeding
Despite this efficient chewing, the cellulose
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 rumen, in
which newly swallowed plant food is stored
and processed for a time
Feeding
The rumen contains thriving colonies of bacteria
that produce enzymes needed to break down
cellulose
After a certain amount of time, the mammal
regurgitates the plant food from the rumen into its
mouth
There the partially digested food is again chewed
and mixed with saliva
“chewing their cud”
The 2nd time the food is swallowed, it moves
through the rest of the digestive tract, where
digestion is completed and nutrients are absorbed
Feeding
Some herbivores, such as rabbits, lack a
rumen but have a large dead-end sac, or
cecum, 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 appendix
A mammal’s teeth provide important clues to its diet.
The sharp, pointed teeth of a wolf show that this animal
is a carnivore. The large flat grinding teeth of a deer
indicate that this animal eats vegetation.
Respiration
All mammals use lungs powered by two sets of
muscles
Chest 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 muscle known as the diaphragm
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 roar, a bark, or even a song
Internal Transport
The mammalian circulatory system is an
arrangement of pumps and blood vessels
The main pump, the heart, 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
kidneys of all vertebrates
Mammalian kidneys extract nitrogenous
wastes from the blood in the form of urea
Urea, water, and other wastes form urine
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
This desert fox survives in areas that
have scant supplies of water. Mammals
that live in desert regions have very
efficient kidneys. Thus their urine
contains little water.
Response
Mammals have the most highly
developed brains of any animals
The brain consists of three parts:
cerebrum, cerebellum, and medulla



Cerebrum: thinking, learning,
understanding
Cerebellum: movement
Medulla: breathing, heart rate
Response
Mammals depend on highly developed
senses to provide themselves with
information about their environment
Eyes vary a great deal from one
mammal species to another
With the exception of apes, monkeys,
and humans, mammals do not see color
well
Response
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 complex behaviors for protection
Compared with other
animals, a mammal has a
large brain. Each
antelope, alert to danger,
is processing a great deal
of information about the
environment in its brain.
If there is real danger, a
delay of a fraction of a
second could mean that
the antelope will not
survive.
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
flexible digits that can grasp vines and branches
Flying mammals have arms modified to support
flaps of skin that form wings
Aquatic mammals have arms modified into
flippers, which they use to control their speed
and direction in the water
This baby monkey swinging from a tree branch
shows only some of the movements mammals are
capable of. Its long tail is useful in maintaining
balance as it moves through the trees.
Reproduction
The three groups of mammals differ greatly in their
methods of reproduction
Egg-laying mammals, the monotremes, are the most
primitive mammals and reproduce much like reptiles
 Oviparous
 Lays eggs that are incubated outside the mothers
body
 Once the young hatch, however, they nurse on milk
provided by the mother
Reproduction
Marsupials are viviparous 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 yolk sac 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 very early
Reproduction
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 marsupium
It spends the next several months there,
growing sufficiently large and independent
so that it can leave the pouch
Reproduction
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 placenta
Nutrients, oxygen, carbon dioxide, and
wastes are exchanged between embryo and
mother through the placenta
Reproduction
The time the embryo spends inside the
uterus is called the gestation period
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 nine
months
Reproduction
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
A platypus is a strange animal. A female
platypus feeds milk to her young – but
only after the young have hatched from
eggs laid by the mother.
The baby kangaroo, safely hitching a ride in
its mother’s pouch, views the world around
it with amusement. If danger threatens,
mother and baby can quickly hop away.
This orangutan mother will care for
her baby for some time. Rarely
setting foot on the ground, the baby
clings tightly to its mother’s fur.
Chapter 33: Mammals
Section 2: Important Orders of
Living Mammals
Important Orders of Living
Mammals
Scientists use several important
characteristics to classify mammals
The structure of teeth and the
number and kinds of bones in the
head are two important features by
which mammals are classified
But perhaps the most important
characteristic used to classify
mammals is the method of
reproduction
Monotremes
Egg-laying mammals
Very rare
Only three species exist today
Live in Australia and New Guinea
 Duckbill platypus
 Echidna (2)
Marsupials
Pouched mammals
Found in Australia
Herbivores that feed primarily on range
grasses
Opossums are the only marsupials found
in North America today
In the past, many other marsupials lived in
South America
Placentals
Living placental mammals are placed in 16
orders
Placental mammals have slightly higher
metabolic rates than those of marsupials
They are also much more abundant than
the marsupials
Order Insectivora
Insect eaters
Includes tree shrews, hedgehogs, shrews,
and moles
Have extremely high metabolic rates and
must eat almost constantly
Order Chiroptera
Contains many different species of bats
Account for ¼ of all mammal species
Many bats are active only at night
Use echolocation to help them navigate
Emit high pitched sounds that bounce off
objects
Colonies of bats sleep together in trees,
hanging upside down and wrapping their
wings around their body
Order Edentata
“Without teeth”
Sloths, anteaters, armadillos
Order Rodentia
Mice, rats, squirrels, beavers, porcupines,
gophers
Two long front teeth that continue to grow
during a rodent’s life
Short gestation period
Order Lagomorpha
Rabbits and hares
Resemble rodents
Sharp front teeth and eat plant material
Their gestation period is short, and the
number of young they produce is high
Order Carnivora
Meat eaters
Cats, dogs, wolves, bears, weasels, hyenas
Most are terrestrial
Kill with sharp teeth and claws
Order Cetacea
Truly aquatic mammals: whales, dolphins,
and porpoises
Have lungs and a circulatory system
designed to permit long, deep dives
Layer of blubber keeps them warm
Have lost both their external ears and their
hind legs
Mate and bear their young in the water
All are carnivores
Order Sirenia
Aquatic animals related to elephants
Peaceful, slow-moving herbivores that live
in rivers and streams in Africa, South
America, and Florida
The manatee, or sea cow, lives in quiet
waters in southern Florida, where it is
often injured by careless boaters
Order Artiodactyla
Contains the large grazing animals: cattle,
sheep, goats, hippopotami, giraffes, and
pigs
The original five toes on each foot have
been reduced to two
Even-toed ungulates
 “hoofed mammal”
Order Perissodactyla
Horses, zebras, tapirs, and rhinoceroses –
the odd-toed ungulates
Have hooves formed from the center toe
of each foot
Order Proboscidea
Mammals with trunks, the great elephants
Only two species, the Indian elephant and
the African elephant still survive
Both species are in danger of becoming
extinct
Order Primates
Includes our own species
Closely related to the ancient insectivores
Most complicated behaviors
Monkeys and apes represent two main
branches within this order
Order Primates
Primates were split apart by the moving
continents
 One branch, the New World monkeys, live
almost entirely in trees
 They have long arms for swinging from branch
to branch and long prehensile tails, which
they use for grasping while climbing
 The other branch, the Old World monkeys lack
prehensile tails
How Mammals Fit into the
World
Herbivorous mammals are major
consumers of plant material
These herbivores are food for carnivorous
mammals
Bats eat mosquitoes and insects
Domesticated mammals provide food in
the form of meat and dairy products
Some mammals carry disease
Others destroy the land around them