Table of Contents – pages iv-v

Unit 1: What is Biology?Unit 2: EcologyUnit 3: The Life of a CellUnit 4: GeneticsUnit 5: Change Through TimeUnit 6: Viruses, Bacteria, Protists, and FungiUnit 7: PlantsUnit 8: InvertebratesUnit 9: VertebratesUnit 10: The Human Body

Unit 1: What is Biology?

Chapter 1: Biology: The Study of LifeUnit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and ConservationUnit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell

Unit 4: Genetics

Chapter 10: Mendel and Meiosis

Chapter 11: DNA and Genes

Chapter 12: Patterns of Heredity and Human Genetics

Chapter 13: Genetic Technology

Unit 5: Change Through Time Chapter 14: The History of Life Chapter 15: The Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Life’s Diversity

Unit 6: Viruses, Bacteria, Protists, and Fungi

Chapter 18: Viruses and Bacteria

Chapter 19: Protists

Chapter 20: Fungi

Unit 7: Plants

Chapter 21: What Is a Plant?

Chapter 22: The Diversity of Plants

Chapter 23: Plant Structure and Function

Chapter 24: Reproduction in Plants

Unit 8: Invertebrates

Chapter 25: What Is an Animal?

Chapter 26: Sponges, Cnidarians, Flatworms, and

Roundworms

Chapter 27: Mollusks and Segmented Worms

Chapter 28: Arthropods

Chapter 29: Echinoderms and Invertebrate

Chordates

Unit 9: Vertebrates Chapter 30: Fishes and Amphibians

Chapter 31: Reptiles and Birds

Chapter 32: Mammals

Chapter 33: Animal Behavior

Unit 10: The Human Body

Chapter 34: Protection, Support, and Locomotion

Chapter 35: The Digestive and Endocrine Systems

Chapter 36: The Nervous System

Chapter 37: Respiration, Circulation, and Excretion

Chapter 38: Reproduction and Development

Chapter 39: Immunity from Disease

Vertebrates

Fishes and Amphibians

Reptiles and Birds

Mammals

Animal Behavior

Chapter 32 Mammals

32.1: Mammal Characteristics

32.1: Section Check

32.2: Diversity of Mammals

32.2: Section Check

Chapter 32 Summary

Chapter 32 Assessment

What You’ll Learn

You will identify the characteristics of mammals.

You will compare and contrast three groups of living mammals and examine their relationships to their ancient ancestors.

• Distinguish mammalian characteristics.

Section Objectives:

• Explain how the characteristics of mammals enable them to adapt to most habitats on Earth.

• Mammals, like birds, are endotherms.

What is a mammal?What is a mammal?

• They have hair and produce milk to nurse their young.

What is a mammal?What is a mammal?

• Mammals also have diaphragms, four-chambered hearts, specialized teeth, modified limbs, and highly developed brains.

• Like feathers, mammalian hair, made out of the protein keratin, is also thought to have evolved from scales.

Mammals have hairMammals have hair


• The arrangement of hair provides insulation and waterproofing and thereby conserves body heat.


• Mammals also have internal feedback mechanisms that signal the body to cool off when it gets too warm.

• Mammals cool off by panting and through the action of sweat glands.

• Panting releases water from the nose and mouth, which results in a loss of body heat.


• Sweat glands help regulate body temperature by secreting moisture onto the surface of the skin.

• As the moisture evaporates, it transfers heat from the body to the surrounding air.

Mammals nurse their youngMammals nurse their young

• Mammals have several types of glands, which are a group of cells that secrete fluids.

• They include glands that produce saliva, sweat, oil, digestive enzymes, hormones, milk, and scent.


• Mammals also feed their young from mammary glands, possibly modified sweat glands, which produce and secrete milk, a liquid that is rich in fats, sugars, proteins, minerals, and vitamins.


• Mammals nurse their young until they are able to digest and absorb nutrients from solid foods.

Respiration and circulation in mammalsRespiration and circulation in mammals• The mammals’ diaphragm helps expand the

chest cavity to aid the flow of oxygen into their lungs.

Position of diaphragm when exhaling

Position of diaphragm when inhaling

Position of ribs when exhaling

Lungs when

exhaling

Position of ribs when inhaling

Lungs when

inhaling

• A diaphragm is the sheet of muscle located beneath the lungs that separates the chest cavity from the abdominal cavity, where other organs are located.

Position of diaphragm when exhaling

Position of diaphragm when inhaling

Respiration and circulation in mammalsRespiration and circulation in mammals

• Mammals have four-chambered hearts in which oxygenated blood is kept entirely separate from deoxygenated blood.

Right atrium

Right ventricle

Left atrium

Left ventricle


• Circulation also removes waste products from cells and helps regulate body temperature.

• Blood helps keep a constant cellular environment, which maintains homeostasis.


• Mammals with teeth have different kinds that are adapted to the type of food the animal eats.

Most mammals have specialized teethMost mammals have specialized teeth

• The pointed incisors of moles grasp and hold small prey.

• The chisel-like incisors of beavers are modified for gnawing.


• A lion’s canines puncture and tear the flesh of its prey.



• Premolars and molars are used for slicing or shearing, crushing, and grinding.

• Many hoofed mammals have an adaptation called cud chewing that enables the cellulose in plant cell walls to be broken down into nutrients they can absorb and use.

• When plant material is swallowed, it moves into the first two of four pouches in the stomach where cellulose in the cell walls is broken down by bacteria.


• The partially digested food, called cud, is repeatedly brought back up into the mouth.


• After more chewing, the cud is swallowed again and when the food particles are small enough they are passed to the other stomach areas, where digestion continues.


Mammals have modified limbsMammals have modified limbs• Mammal limbs are

adapted for a variety of methods of food gathering.

• Primates, for example, use their opposable thumb to grasp objects—including fruits and other foods.

Mammals can learnMammals can learn

• Mammals can accomplish complex behaviors, such as learning and remembering what they have learned.


• Primates, including humans, are perhaps the most intelligent animals.


• Chimpanzees, for example, can use tools, work machines, and use sign language to communicate with humans.

Motor areaSensory area

Language area

Vision area

General interpretation

area

Cerebrum

Speech area

Taste area

Intellect, learning, and personality

Hearing area

Brain stem Cerebellum

Balance area


A MammalA Mammal

Glands

Diaphragm Heart

Teeth

Mammary glandsHair

Question 1

What two characteristics do mammals have that no other animal has? (TX Obj 2; 8C)

Answer

All mammals have hair and produce milk to nurse their young.

What do scientists believe mammalian hair evolved from?(TX Obj 2; 8C)

D. keratin C. skin B. scales A. feathers

Question 2

The answer is B. Like feathers, hair also is made out of keratin which leads scientists to believe that hair evolved from scales.

How do a mammal’s teeth help it obtain food?(TX Obj 2; 8C)

Question 3

Mammals have teeth that are adapted to the type of food they eat. Canine teeth puncture and tear the flesh of prey. Premolars and molars are used for slicing, shearing, and crushing while incisors are used for gnawing and grasping.

Which of the following helps a mammal take in large amounts of oxygen?(TX Obj 2; 8C, 10A)

D. diaphragm

C. teeth

B. heart A. glands

Question 4

The answer is D, diaphragm.

Glands

Diaphragm Heart

Teeth

Mammary glandsHair

• Distinguish among the three groups of living mammals.

Section Objectives:

• Compare reproduction in egg-laying, pouched, and placental mammals.

Mammal ClassificationMammal Classification

• Scientists place mammals into one of three subclasses based on their method of reproduction.

Placental mammals: A great successPlacental mammals: A great success

• Placental mammals give birth to young that have developed inside the mother’s uterus until their body systems are fully functional and they can live independently of their mother’s body.


• The uterus is a hollow, muscular organ in which offspring develop.

• Nourishment of the young inside the uterus occurs through an organ called the placenta which develops during pregnancy.


• The time during which placental mammals develop inside the uterus is called gestation.

• Development inside the mother’s body ensures that the offspring are protected from predators and the environment during the early stages of development.

Pouched mammals: The marsupialsPouched mammals: The marsupials• A marsupial is a mammal

in which the young have a short period of development within the mother’s body, followed by a period of development inside a pouch made of skin and hair on the outside of the mother’s body.

Pouched mammals: The marsupialsPouched mammals: The marsupials

• Most marsupials are found in Australia and surrounding islands.

• Scientists have found fossil marsupials on the continents that once made up Gondwana.

• These fossils support the idea that marsupials originated in South America, moved across Antarctica, and populated Australia before Gondwana broke up.

Monotremes: The egg layersMonotremes: The egg layers

• The duck-billed platypus is a monotreme, a mammal that reproduces by laying eggs.

• Spiny anteaters, also called echidnas, belong to this subclass as well.


• Monotremes are found only in Australia, Tasmania, and New Guinea.

• Only three species of monotremes are alive today.


• The platypus, a mostly aquatic animal, has a broad, flat tail, much like that of a beaver.

• Its rubbery snout resembles the bill of a duck.


• The platypus has webbed front feet for swimming through water, but it also has sharp claws on its front and hind feet for digging and burrowing into the soil.

• Much of its body is covered with thick, brown fur.

• The spiny anteater has course, brown hair, and its back and sides are covered with sharp spines that it can erect for defensive purposes when threatened by enemies.


• The first placental mammals appeared in the fossils record about 125 million years ago.

• Scientists trace the origins of placental mammals from a group of mouse-sized animals to a group of reptilian ancestors called therapsids.

Origins of MammalsOrigins of Mammals

Origins of MammalsOrigins of Mammals• Therapsids had features of both reptiles and

mammals.

• They existed between 270 and 180 million years ago.

• The mass extinction of the dinosaurs at the end of the Mesozoic Era, along with the breaking apart of Pangaea and changes in climate, opened up new niches for early mammals to fill.

• The Cenozoic Era is sometimes called the golden age of mammals because of the dramatic increase in their numbers and diversity.



Carnivores 270 species

Artiodactyls 220 species

Cetaceans 79 species

Rodents 2000 species

Chiropterans 925 species

Proboscids 2 species

Insectivores 375 species

Primates 230 species

Perissodactyls 270 species

Marsupials 280 species

Monotremes 3 species

Placental mammals

4400 species

Therapsids mammal-like

reptiles ReptilesAmphibians

FishesInvertebrates

Species numbers are approximate and subject to change pending discoveries or extinctions.

Which of the following is NOT an example of a placental mammal? (TX Obj 2; 8C)

Question 1

D. fox

C. dog

B. human

A. kangaroo

The answer is A. A kangaroo is a marsupial.

What three events allowed mammals to fill new niches? (TX Obj 3; 7B)

Question 2

Answer

The mass extinction of the Mesozoic Era, the break up of Pangaea, and changes in climate opened up new niches for early mammals to fill.

What is the difference between a monotreme and a marsupial? (TX Obj 2; 8C, 10A)

Question 3

Monotremes reproduce by laying eggs. A marsupial’s young begins development within the body but complete its development outside the body in a pouch made of skin and hair.

• Mammals are endotherms giving them the ability to maintain a fairly constant body temperature.

Mammal Characteristics

• Hair is present on all mammals at some point in their lives.

• Mammals feed their young from modified sweat glands called mammary glands.

• Mammals with teeth have different kinds of teeth that are adapted to the type of food they eat.

Mammal Characteristics

• Highly developed brains enable mammals to learn.

• Mammals are classified into three subclasses—placentals, marsupials, and monotremes—based on how they reproduce.

Diversity of Mammals

• Placental mammals carry young inside the uterus until their body systems are fully functional. Nourishment inside the uterus occurs through an organ called the placenta.

• Marsupials carry partially developed young in a pouch on the outside of the mother’s body.

Diversity of Mammals

• Monotremes are egg-laying mammals found only in Australia, Tasmania, and New Guinea.

Question 1

How many groups are mammals classified into? (TX Obj 2; 8C)

D. four

C. three

B. two

A. one

The answer is C. Mammals are classified as placental, marsupial, or as monotremes.

Question 2Of the teeth shown, which set would most likely be used by an animal that feeds on grass?(TX Obj 2; 8C)

D.

C.

B.

A.

The answer is A. This skull contains primarily molars and premolars which are used to crush and grind food.

Question 3

What role do zoos play in the preservation of endangered species?

Answer

Zoos use captive breeding programs to increase populations of animals, educate the public, conduct research, and provide professional training for staff.

Question 4

Which organ in this mammal is responsible for keeping oxygenated and deoxygenated blood separate? (TX Obj 2; 8C, 10A)

The heart enables mammals to keep oxygenated and deoxygenated blood separate. This helps them maintain their high metabolism.

Heart

Question 5

Which of the following is one way that mammals cool off? (TX Obj 2; 8C)

D. by hibernating

C. by panting

B. by shedding

A. by swimming

The answer is C. Mammals cool off by panting and through the action of sweat glands.

Question 6

Why are mammals considered to be one of the most successful groups of organisms?(TX Obj 2; 8C)

Mammals are capable of accomplishing complex behaviors such as learning and remembering what they have learned. Mammals also guard their young and teach them the skills they need to survive on their own.

Question 7

While walking through the forest, you find an animal skull. You notice that the teeth in the skull are primarily pointed and long. What can you infer about the diet of the animal?(TX Obj 2; 8C)

The animal was most likely a carnivore. Long, pointed incisors and canines are used to stab and tear flesh.

Photo CreditsPhoto Credits

• Digital Stock

• PhotoDisc

• Bill Tarpenning/USDA

• Digital Vision

• Alton Biggs

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