MammalsMammals

840

What You’ll Learn■ You will identify the charac-

teristics of mammals.■ You will compare and contrast

three groups of living mam-mals and examine their rela-tionships to their ancientancestors.

Why It’s ImportantMammals play a major role in most ecosystems on Earthbecause they are one of themost successful groups of ani-mals. Humans are mammals, sostudying mammal characteristicsprovides information abouthumans as well.

Visit to• study the entire chapter

online• access Web Links for more

information and activities onmammals

• review content with theInteractive Tutor and self-check quizzes

Giraffes are the tallest mam-mals. Newborn giraffes average1.8 meters and can grow to beabout 5.5 meters as adults. Theyhave long legs and can runquickly—about 60 km/h. Theirlong legs, as well as their longnecks, help them reach leaves intall acacia trees.

Understandingthe Photo

ca.bdol.glencoe.com

Shin Yoshino/Minden Pictures

0840-0840 C32CO BDOL-829900 8/4/04 11:01 PM Page 840

Mammal Characteristics32.1SECTION PREVIEWObjectivesDistinguish mammaliancharacteristics.Explain how the charac-teristics of mammalsenable them to adapt tomost habitats on Earth.

Review Vocabularymetabolism: all of the

chemical reactions that occur within anorganism (p. 147)

New Vocabularyglandmammary glanddiaphragm

32.1 MAMMAL CHARACTERISTICS 841

What is a mammal?Mammals, like birds, are endotherms. The ability to maintain a fairly

constant body temperature enables mammals to live in almost every pos-sible environment on Earth. Mammals have important characteristics notfound in other animals. They have hair and produce milk to nurse theiryoung. Mammals also have diaphragms, four-chambered hearts, special-ized teeth, modified limbs, and highly developed brains.

Mammals have hairHave you ever heard someone complain about a pet that is shedding

its hair? There’s no doubt that such a pet is a mammal because hair ispresent on all mammals at some point in their lives. Like feathers,mammalian hair, made out of the protein keratin, is also thought tohave evolved from scales. The arrangement of hair provides insulationand waterproofing and thereby conserves body heat. If you have everworn a wool sweater made from the hair of a sheep, you know howwarm wool can be on a cold day. As shown in Figure 32.1 on the nextpage, hair also serves other functions.

Although hair helps retain body heat, mammals also have internal feed-back 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.

Find Main Ideas As you read Chapter 32, list the main characteristics of mammals on the tabs. As you learn about the main characteristics, write a benefit of the adaptation under the tab for each.

Mammals Make the following Foldable to help you identifymain characteristics of mammals.

Fold a vertical sheet of notebook paper from side to side.

Cut along every fourth line of only the top layer to form tabs.

Label each tab.

STEP 1

STEP 3

STEP 2

PhysicalScience

Connection

Movement ofheat throughhair Compared tosolids or liquids,gases are poorconductors ofheat. A layer ofhair or fur on amammal’s skincontains many airpockets trappedbetween the hairshafts. Because airis a poor heatconductor, heatmoves slowlythrough an airpocket. As a result,the rate at whichheat is lost by themammal isreduced.

0841-0847 C32S1 BDOL-829900 8/4/04 10:39 PM Page 841

Figure 32.1Hair helps maintain a constant bodytemperature. It also serves a varietyof other purposes.

Mice have four to nineoffspring in each litter, and upto 17 litters a year. The youngnurse for just a few weeks.

B

An Indian rhinoceros usually has one calf at a time.Calves begin to graze at two months of age.

A

The white patch of hair on the rump of the fleeingdeer signals danger to othermembers of the herd.

C

The sharp, barb-tippedquills of a porcupine area type of modified hair.

A

The black stripes of a tiger’s furaid in camouflaging this beautifulcat as it hunts for prey.

B

842

Panting releases water from the noseand mouth, which results in a loss ofbody heat. Sweat glands help regulatebody temperature by secreting mois-ture onto the surface of the skin. As themoisture evaporates, it transfers heatfrom the body to the surrounding air.

Mammals nurse their youngMammals have several types of

glands, which are a group of cells thatsecrete fluids. They include glands thatproduce saliva, sweat, oil, digestiveenzymes, hormones, milk, and scent.

You have already learned how sweatglands help keep a mammal cool.

Mammals also feed their youngfrom mammary (MA muh ree) glands,possibly modified sweat glands, whichproduce and secrete milk, a liquid thatis rich in fats, sugars, proteins, miner-als, and vitamins. Mammals nurse theiryoung until they are able to digest andabsorb nutrients from solid foods.Figure 32.2 shows that the number ofyoung each mother has and the lengthof time she nurses her young varyamong species.

Figure 32.2Large mammals usuallyhave few young. InferWhy do mammals thatare prey for manypredators tend tohave larger litters?

(tl)N

igel

J.D

enni

s/P

hoto

Res

earc

hers

, (t

c)R

enee

Lyn

n/P

hoto

Res

earc

hers

, (t

r)S

teph

en J

.Kra

sem

ann/

DR

K P

hoto

, (b

l)M.C

.Cha

mbe

rlain

/DR

K P

hoto

, (b

r)To

m M

cHug

h/P

hoto

Res

earc

hers

0841-0847 C32S1 BDOL-829900 8/4/04 10:40 PM Page 842

Respiration and circulation in mammals

Mammals need a high level ofenergy to maintain their endother-mic metabolism. This energy level is sustained when large amounts ofnutrients and oxygen enter the bodyand reach the cells.

The mammals’ diaphragm helpsexpand the chest cavity to aid the flowof oxygen into their lungs. Adiaphragm (DI uh fram) is the sheet ofmuscle located beneath the lungs thatseparates the chest cavity from theabdominal cavity, where other organsare located. Once in the lungs, oxygendiffuses into the blood. As the chestcavity returns to its resting position,air is released.

Mammals, like birds, have four-chambered hearts in which oxygen-ated blood is kept entirely separatefrom deoxygenated blood. This en-sures that a good supply of nutrientsand oxygen are delivered to cells whichsupports their endothermic metabo-lism. Circulation also removes wasteproducts from cells and helps regulatebody temperature. Blood helps keep aconstant cellular environment, whichmaintains homeostasis.

Most mammals have specialized teeth

Teeth are a distinguishing featureof most mammals. Although fishesand reptiles have teeth, their teeth arerelatively uniform and are used pri-marily for tearing, grasping, andholding prey.

Mammals with teeth have differentkinds that are adapted to the type offood the animal eats. Think of the dif-ferent tools you might use to build apiece of furniture, such as a chisel forscraping or a saw for cutting. Like acabinetmaker’s tools, teeth are shapedto match the types of jobs they do.

The pointed incisors of molesgrasp and hold small prey. The chisel-like incisors of beavers are modifiedfor gnawing. A lion’s canines punc-ture and tear the flesh of its prey.Premolars and molars are used forslicing or shearing, crushing, andgrinding. You can get a closer look atmammalian teeth in the MiniLab onthis page. By examining the teeth of amammal, a scientist can determinewhat kind of food it eats.

Many hoofed mammals have anadaptation called cud chewing thatenables the cellulose in plant cellwalls to be broken down into nutri-ents they can absorb and use.

32.1 MAMMAL CHARACTERISTICS 843SIU/Photo Researchers

PhysicalScience

Connection

Teeth as simplemachines Teethand chisels areshaped like wedges.A wedge is a simplemachine thatincreases an appliedforce and changesits direction. As aresult, a downwardforce applied to atooth is changed toa larger sidewaysforce.

Compare and ContrastAnatomy of a Tooth Most mammals have teeth. Teeth are adapted to a mammal’s diet.

Procedure! Examine a prepared longitudinal

section view slide of a human toothunder low-power magnification. CAUTION: Use caution when workingwith a microscope and slides.

@ Locate the different areas—enamel, dentine, and pulp cav-ity—that form the tooth. Move the slide to see all areas.

# Diagram the tooth as it appears under low power.

Analysis1. Explain Most of the tooth you

studied is composed of the rootunder the gums. How is the partabove the gum adapted to thediet of humans?

2. Interpret ScientificIllustrations Examine the diagrams of mammal skulls and predict what kinds of food thesemammals might eat based on the shape of their teeth.

Longitudinalsection of acanine tooth

0841-0847 C32S1 BDOL-829900 8/4/04 10:40 PM Page 843

844 MAMMALS(t)Lisa & Mike Husar/DRK Photo, (c)Eastcott/Momatiuk/Animals Animals, (b)E. Hanumantha Rao/Photo Researchers

Figure 32.3Mammal groups are distinguishedby number and types of teeth.

Premolars and molars are the predominantteeth in horses and other herbivores. Thesecrushing and grinding teeth are covered withhard enamel.

C

Carnivores, such as this tiger, have canine teeththat stab and pierce food, and premolars andmolars adapted for chewing.

B

Bears, like humans, have incisors, canines,premolars, and molars. Bears and humansare omnivores.

A

Have you ever seen cows slowly chewing while lying in a pasture?When plant material is swallowed, itmoves into the first two of fourpouches in the stomach where cellu-lose in the cell walls is broken downby bacteria. The partially digestedfood, called cud, is repeatedly broughtback up into the mouth. After morechewing, the cud is swallowed againand when the food particles are smallenough they are passed to the otherstomach areas, where digestion con-tinues. You can learn more aboutdigestion in mammals in the Problem-Solving Lab on this page. The varioustypes of teeth in different mammalscan be seen in Figure 32.3.

Data Table

Animal Length of Diet AnimalDigestive Tract Category Mass

Koala 305 cm Herbivore 10 kg

Dog 135 cm Carnivore 11 kg

Rabbit 272 cm Herbivore 9 kg

Bobcat 145 cm Carnivore 12 kg

Analyze InformationWhich animal has the longest digestive system? A mam-mal may be an herbivore, carnivore, or omnivore. Is there a rela-tionship between length of a mammal’s digestive tract and itsdiet? Make a hypothesis as to what that correlation might be.

Solve the ProblemThe following data table provides general information ondigestive tracts for several mammals.

Thinking Critically1. Analyze What does the relationship between diet and

digestive tract length appear to be?2. Interpret Data Do the data support your hypothesis?

Explain your answer.3. Formulate a Hypothesis Explain the relationship

between digestive tract length and difficulty in digestingfood type. (Hint: Does cellulose take longer to digest?)

4. Conclude Was the mass of all animals relatively close whencompared? Explain why mass is important.

0841-0847 C32S1 BDOL-829900 8/4/04 10:41 PM Page 844

Mammals have modified limbs Mammals have several adaptations

that help them meet their energy needs.For example, mammal limbs areadapted for a variety of methods of food gathering. Recall that primates use their opposable thumb to graspobjects—including fruits and otherfoods. Figure 32.4 illustrates otherlimb modifications in mammals. Youcan see the bones of mammal limbs andother parts of mammalian skeletons inthe MiniLab on this page. Refer toFigure 32.5 on the next page for a sum-mary of mammalian characteristics.

Mammals can learnOne reason mammals are successful

is that they guard their young fiercelyand teach them survival skills. Mam-mals can accomplish complex behav-iors, such as learning and rememberingwhat they have learned.

32.1 MAMMAL CHARACTERISTICS 845(tl)Bill Beatty/Animals Animals, (tr)Ken Brate/Photo Researchers, (b)Stephen Dalton/Photo Researchers

Figure 32.4The front limbs of moles are powerful and short, with large claws that enable them to dig through dirt. Bats have elongated finger bones that support the flight membranes of their wings.

ObserveMammal Skeletons Owls arepredators. They feed on smallmammals as well as onbirds. After eating a meal,the tough indigestible partsof prey, such as bones, areregurgitated as pellets. Theskeletons of a variety of smallmammals can be studied by examining owl pellets.

Procedure! Place an owl pellet onto a sheet of paper toweling. @ Use a forceps to remove a small amount of the outer

covering.# Prepare a wet mount of this material and observe under

low-, then high-power magnification. Diagram what yousee. Use forceps to open the pellet and remove all bonesthat are present. Look especially for skulls. (Note: Skullsmay be small and certain parts, such as lower jaws, will beseparated.)

$ Identify mammalian skulls using diagrams A and B as a guide.

% Attempt to reconstruct the skeleton for an entire animal.You may wish to glue the skeletal pieces onto a piece ofcardboard. Dispose of materials appropriately. CAUTION:Wash your hands after handling animal materials.

Analysis1. Understand What was the outer covering on the pellet?

What does this tell you about the contents of the pellet?Explain.

2. Interpret Data How many vole and shrew skulls werepresent in your pellet?

3. Explain How were you able to differentiate the skulls ofthese two mammals?

4. Predict Are voles and shrews herbivores or carnivoresbased on appearance of their teeth? Explain.

Owl pellet

Shrew

Vole

AA

BB

0841-0847 C32S1 BDOL-829900 8/4/04 10:42 PM Page 845

Wayne Lynch/DRK Photo

Teeth A fox’steeth indicate whatit eats and how it gets food. Itscanines are used topuncture and tearthe flesh of prey. Its molars slice andcrush the fleshbefore swallowing.

AA

BB

DD

CC

Red fox

A MammalFigure 32.5A red fox, a member of the dog family, can be found in opencountry and forests throughout the United States. Red foxes areactive at night, and feed on insects, birds, rodents, rabbits,berries, and fruit. Critical Thinking Using the informationgiven below, explain how a fox is able to maintain aconstant body temperature.

Glands Most mammalshave sweat, oil, mammary,and scent glands in theirskin. Sweat glands helpmammals cool off. Oilglands lubricate the hairand skin. Foxes use theirscent glands to mark newterritories.

Diaphragm Thediaphragm is a muscle thathelps the chest cavity expandto take in large amounts ofoxygen used to maintain thehigh metabolism of all mam-mals. It separates the chestand abdominal cavities.

Heart The four-chambered heart of mam-mals enables them to keep oxygenated anddeoxygenated blood separate. This helpsthem maintain their high metabolism.

846 MAMMALS

FF Hair Dense, soft underhair insulates the fox by trappingwarm air next to its body. The coarse, long guard hairsprotect against wear and may be colored for camouflage.The fox sheds its coat little by little during the summer.

EE Mammary glands Like all female mam-mals, a female fox nourishes her youngwith milk from her mammary glands.

0841-0847 C32S1 BDOL-829900 8/4/04 10:42 PM Page 846

Have you ever attended an aquariumshow or watched a movie about per-forming dolphins and whales? Dol-phins exhibit a wide variety of learnedbehaviors, including the behaviors per-formed for films or in aquarium shows.

Primates, including humans, areperhaps the most intelligent animals.Chimpanzees, for example, can usetools, illustrated in Figure 32.6, workmachines, and use sign language to communicate with humans. Mam-malian intelligence is a result of com-plex nervous systems and highlydeveloped brains. The outer layer of amammalian brain often is folded,forming ridges and grooves. Theseridges and grooves increase thebrain’s active surface area.

Explain whatenables mammals to be intelligent.

Understanding Main Ideas1. Name four characteristics of mammals.

2. Describe three mammal adaptations for obtainingand consuming food.

3. Identify and describe the relationship betweeninternal feedback mechanisms and the mainte-nance of body temperatures.

4. How does intelligence benefit mammals?

5. Explain how the interrelationship between respiration and circulation sustains a mammal’smetabolism.

Thinking Critically6. Suppose you are a mammal that feeds on pine

seeds and lives in a forest in a cold region. Describethe adaptations that would help you survive.

7. Observe and Infer On an archaeological dig,you find a skull about 5 cm long with two chisel-shaped front teeth and several flattened backteeth. Is this a skull from a mammal? Explain youranswer. For more help, refer to Observe and Inferin the Skill Handbook.

SKILL REVIEWSKILL REVIEW

32.1 MAMMAL CHARACTERISTICS 847(t)George D. Lepp/Photo Researchers, (b)Gunter Ziesler/Peter Arnold, Inc.

Animal Trainer

I f you seem to get along wellwith animals, consider a

career as an animal trainer. Ajob as a trainer can be hard tofind, but fun and rewarding.

Skills for the JobSome animal trainers work in

zoos or aquariums, teaching monkeys,parrots, seals, and other animals to performspecific behaviors. Some trainers work with race horses, andothers teach police dogs to sniff out explosives or guidedogs to help people with physical limitations. Many trainersbegin as animal keepers. A position at a dog obedienceschool may require only on-the-job experience, but if youwant to train guide dogs, you must complete a three-yearcourse of study. To train dolphins at a large aquarium, youmust have a two- or four-year degree in psychology or biol-ogy. If you want to narrate the shows, you must also be agood public speaker.

For more careers in related fields, visitca.bdol.glencoe.com/careers

Figure 32.6A chimpanzee using a stick to get insects outof a tree trunk demonstrates that mammalsother than humans are also intelligentenough to make and use tools.

ca.bdol.glencoe.com/self_check_quiz

0841-0847 C32S1 BDOL-829900 8/4/04 10:43 PM Page 847

32.2SECTION PREVIEWObjectivesDistinguish among thethree groups of livingmammals.Compare reproduction inegg-laying, pouched, andplacental mammals.

Review Vocabularyendangered species: a

species in which thenumber of individualsfalls so low that extinc-tion is possible (p. 115)

New Vocabularyplacental mammaluterusplacentagestationmarsupialmonotremetherapsid

848 MAMMALS

Analyzing Mammalian ClassificationFinding Main Ideas On a piece of paper, construct an outline about mam-mal classification. Use the red and blue titles in this section as a guideline. As you read the paragraphs that follow the titles, add important information and vocabulary words to your outline.

Example:I. Mammal Classification

A. Placental mammals1.

B. Pouched mammals1.

C. Monotremes1.

Use your outline to help you answer questions in the section assessmenton page 851. For more help, refer to Outline in the Skill Handbook.

Mammal ClassificationLiving in the United States, you are probably familiar with

only one of the three subclasses, of the class Mammalia—placental mammals. Scientists place mammals into one of threesubclasses based on their method of reproduction.

Placental mammals: A great successPlacental mammals give birth to young that have developed

inside the mother’s uterus until their body systems are fully func-tional and they can live independently of their mother’s body.The uterus (YEWT uh rus) is a hollow, muscular organ in whichoffspring develop. Nourishment of the young inside the uterusoccurs through an organ called the placenta (pluh SEN tuh),which develops during pregnancy. The placenta passes nutrientsand oxygen to and removes wastes from the developing embryo.The time during which placental mammals develop inside theuterus is called gestation (jeh STAY shun). The kits shown inFigure 32.7 were born after a period of gestation.

Diversity of Mammals

(t)Fred Bruemmer/DRK Photo, (b)Steve Maslowski/Photo Researchers

Figure 32.7The length of gestation varies fromspecies to species in placental mammals.These raccoon kits were born after nineweeks of gestation. Gestation of mice is21 days, whereas gestation for a rhino-ceros is about 14 to 16 months.Hypothesize Why do larger mam-mals have longer gestation times?

Plains of America with bison

0848-0857 C32S2 BDOL-829900 8/4/04 10:23 PM Page 848

Development inside the mother’sbody is an adaptation that played amajor role in the success of mammals.It ensures that the offspring are pro-tected from predators and the envi-ronment during the early stages ofdevelopment.

About 90 percent of all mammalsare placentals. You can learn moreabout placental mammals on pages1086–1089 in the Focus On.

Pouched mammals: The marsupials

Marsupials make up the secondsubclass of mammals. A marsupial(mar SEW pee uhl) is a mammal inwhich the young have a short periodof development within the mother’sbody, followed by a period of devel-opment inside a pouch made of skinand hair on the outside of themother’s body. You may have seen theonly North American marsupial, the

opossum. Most marsupials are foundin Australia and surrounding islands.The theory of plate tectonics explainswhy most marsupials are found inAustralia today. Scientists have foundfossil marsupials on the continentsthat once made up Gondwana. Thesefossils support the idea that marsupi-als originated in South America,moved across Antarctica, and popu-lated Australia before Gondwanabroke up.

Ancestors of today’s marsupialswere able to populate the landmassthat became Australia without havingto share the area with the competitiveplacental mammals that evolved inother places. They successfully spreadout and filled niches similar to thosethat placental mammals filled in allother parts of the world, as you cansee in Figure 32.8. In fact, sincehumans introduced sheep, rabbits,and other placental mammals to

32.2 DIVERSITY OF MAMMALS 849

gestation fromthe Latin wordgestare, meaning“to bear”; Gesta-tion is time duringwhich a placentalmammal developsin a uterus.

(t)Sidney Bahart/Photo Researchers, (cl)Tom Brakefield/DRK Photo, (cr)Mickey Gibson/Animals Animals, (b)Fritz Prenzel/Animals Animals

Figure 32.8In Australia and Tasmania, many marsupials fillniches that are occupied by placental mammalson other continents.

The giant ant-eater of Mexico,a placentalmammal, has along, stickytongue that ituses to collectants and termitesfrom their nests.

A

The numbat, a marsupial,lives in Australia. It has along, sticky tongue that ituses to eat termites and ants.

B

The ring tailed lemur, a placental mammal,lives in trees on the island of Madagascar. Itis active by day, and eats fruits, leaves, andoccasionally insects.

D

The spotted cuscus ofAustralia, a marsupial,lives in trees. It is asolitary, nocturnalanimal that eats fruit,leaves, bark, insects,small mammals,reptiles, and birds.

C

0848-0857 C32S2 BDOL-829900 8/4/04 10:24 PM Page 849

Australia, many of the native marsu-pial species have become threatened,endangered, or even extinct.

Infer why some mar-supials have become threatened inAustralia.

Monotremes: The egg layersDo you think the animal shown

in Figure 32.9B is a mammal? It hashair and mammary glands, yet it layseggs. The duck-billed platypus is amonotreme (MA nuh treem), a mam-mal that reproduces by laying eggs.

850 MAMMALS(t)Tom McHugh/Photo Researchers, (b)Klaus Uhlenhut/Animals Animals

Artiodactyls220 species

Carnivores270 species

Cetaceans79 species

Rodents2000 species

Marsupials280 species

Placentalmammals

4120 species

Monotremes3 species

Proboscids3 species

Insectivores375 species

Chiropterans925 species

Primates230 species

Perissodactyls18 species

Therapsidsmammal-like

reptiles

Reptiles

Amphibians

Invertebrates

Fishes

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

Figure 32.10This diagram representsthe orders of mammals,gives the approximatespecies number, andshows their evolutionaryrelationships.

AA

BB

Figure 32.9Present-day mono-tremes include one species of platypus andtwo species of echidnas.This echidna species isfound only in Australiaand nearby islands (A).The duck-billed platypushas several physicalfeatures that seem tobelong to a variety of other animals (B).

ANIMALS

0848-0857 C32S2 BDOL-829900 8/4/04 10:25 PM Page 850

Spiny anteaters, also called echidnas,belong to this subclass as well.Monotremes are found only in Aus-tralia, Tasmania, and New Guinea.One of the two species of spinyanteaters can be found only in NewGuinea. Only three species of mono-tremes are alive today.

The platypus, a mostly aquatic ani-mal, has a broad, flat tail, much likethat of a beaver. Its rubbery snoutresembles the bill of a duck. Theplatypus has webbed front feet forswimming through water, but it alsohas sharp claws on its front and hindfeet for digging and burrowing intothe soil. Much of its body is coveredwith thick, brown fur.

The spiny anteater has coarse,brown hair, and its back and sides arecovered with sharp spines that it canerect for defensive purposes whenthreatened by enemies. From itsmouth, the anteater extends its long,sticky tongue to catch insects.

Origins of MammalsPresent-day mammal orders are

shown in Figure 32.10. The first placental mammals appeared in the fos-sil record about 125 million years ago.Scientists trace the origins of placentalmammals from a group of mouse-sizedanimals, such as Eomaia represented

in Figure 32.11A, to a group ofreptilian ancestors called therapsids.Therapsids (ther AP sidz), representedin Figure 32.11B, had features of bothreptiles and mammals. They existedbetween 270 and 180 million years ago.

The mass extinction of the dino-saurs at the end of the Mesozoic Era,along with the breaking apart ofPangaea and changes in climate,opened up new niches for early mam-mals to fill. The appearance of flower-ing plants at the end of this era suppliednew living areas, food sources, andshelter. Some mammals that movedinto the drier grasslands became fast-running grazers, browsers, and preda-tors. The Cenozoic Era is sometimescalled the golden age of mammalsbecause of the dramatic increase intheir numbers and diversity.

Understanding Main Ideas1. Describe the characteristics of placental mammals.

2. Compare monotremes and marsupials.

3. Why are monotremes classified as mammals?

4. What are therapsids and what is their relationshipto mammals?

Thinking Critically5. There are several marsupial species in South

America, but only one species is native to North

America. Make a hypothesis about the presence or absence of marsupial species in Europe. Howcould you test your hypothesis?

6. Get the Big Picture You find a mammal fossiland observe the following traits: hooves, flat-tened teeth, skeleton the size of a large dog.What can you infer about its way of life? Formore help, refer to Get the Big Picture in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

32.2 DIVERSITY OF MAMMALS 851

AA

BB

Figure 32.11(A) Eomaia is the oldestplacental mammal fossildiscovered. Anatomicalevidence shows that itmay have lived in trees.(B) Therapsids were theancestors of mammals.The lower jaw and mid-dle ear bones of therap-sids were like those ofreptiles. However, theyhad straighter legs thanreptiles and held themcloser to the body.

ca.bdol.glencoe.com/self_check_quiz

0848-0857 C32S2 BDOL-829900 8/4/04 10:25 PM Page 851

852 MAMMALS

Before YouBegin

Dogs make great compan-ions. They provide theirowners with an opportu-nity to love and nurtureanother living thing. Inreturn, they are loyal,offer protection to theirowners, and are fun tohave around. Dogs havebeen bred for a variety ofreasons. Some are workingdogs, such as herders,sporting dogs, sled dogs,and guide dogs. Othershave been bred for racing,while others are showdogs. However, all of thesebreeds have the samebasic dog characteristics.

Adaptations in Breeds of Dogs

ProblemWhat adaptations are important to various breeds of dogs.

ObjectivesIn this BioLab, you will:■ Observe the characteristics of dogs.■ Record the adaptations of different dog breeds.■ Use the Internet to collect and compare data from other

students.■ Compare and contrast the characteristics of breeds of dogs.

Materialsaccess to the Internet

Skill HandbookIf you need help with this lab, refer to the Skill Handbook.

1. Make a copy of the data table.2. Visit to find links

to sites that describe breeds of dogs.3. Find pictures and descriptions of these dogs. Record

the physical characteristics unique to each breed in the data table.

PROCEDUREPROCEDURE

PREPARATIONPREPARATION

ca.bdol.glencoe.com/internet_lab

Ken

t &

Don

na D

anne

n/P

hoto

Res

earc

hers

0848-0857 C32S2 BDOL-829900 8/4/04 10:27 PM Page 852

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Compare and Contrast Alaskan Malamutes, Greyhounds,Samoyeds, Siberian Huskys, and Whippets are all built forrunning. How are they similar and how arethey different?

2. Determine Which dogs would make goodguide dogs? Why?

3. Explain Why would a Collie make a goodherder?

4. Apply Assume you work for a local nursinghome and are asked to find a dog that couldlive in the home and be a good companionand perhaps even help some of the residents.Go to and select a breed of dog you think would beadapted for this work. Explain your reasoning.

Find this BioLab using the link below, andpost the data tables provided for this activity.Using the additional data from other stu-dents on the Internet, analyze the combineddata and complete your table.

ca.bdol.glencoe.com/internet_lab

32.2 DIVERSITY OF MAMMALS 853

Dogs

Breed Physical Temperament ClassificationCharacteristics

Alaskan Malamute

Australian Cattle Dog

Collie

German Shepherd Dog

German Shorthaired Pointer

Greyhound

Labrador Retriever

Old English Sheepdog

Samoyed

Siberian Husky

Whippet

Rough Collie

4. Record the temperaments of each breed in thedata table.

5. Find links at to find information on dogs that are classified asworking dogs, herding dogs, sporting dogs, andhounds.

6. Record the classification of each breed in thedata table.

ca.bdol.glencoe.com/internet_lab

ca.bdol.glencoe.com/internet_lab

John Henley/The Stock Market

0848-0857 C32S2 BDOL-829900 8/4/04 10:31 PM Page 853

Zoos were originally created for public enter-tainment. They began as a result of people’s

interest in exotic animals. The animals were keptin small cages with little attention given to theirneeds. Soon, however, people began to realize theanimals needed more than food and basic shelter.Zoos began providing better surroundings for theanimals, and giving the public information aboutanimals and their natural habitat.

Modern zoos In modern zoos, animals arerarely kept in tiny cages. During the 20th century,zoos began providing a new experience for visitorsby replacing the bars and walls of cages with pro-tective moats and larger animal areas. But space isoften limited so architects struggle to make exhibitareas look large and interesting to their inhabi-tants and visitors. Many zoos also have enrichmentprograms that provide animals with activities simi-lar to those they would participate in if they wereliving in the wild. Zookeepers give animals games,

puzzles (such as fish stuffed into a block of ice forpolar bears to dig out), slides, pools, and streams,as well as other items that simulate their naturalenvironment.

Captive breeding Ensuring a future for theworld’s animals has become as much a priority forzoos as displaying them. Zoos use captive breedingto increase their populations. The animals beloware results of captive breeding. Advances in captivebreeding techniques, such as artificial inseminationand in vitro fertilization, have drawn public atten-tion to the potential for rescuing species. In somecases, captive breeding has meant the differencebetween survival and extinction of a species.However, there is not enough room in zoos tohouse many extra animals, and since some animalscan be domesticated in as little as two generations,few species can survive in the wild after beingraised for generations in captivity. Other limita-tions of captive breeding include inbreeding(which decreases the genetic diversity of the popu-lation), low fertility rates, lack of funding for pro-grams, and diseases spread by contact with speciesnot encountered in the wild.

Conservation Zoos also help preserve bio-diversity through public education, professionaltraining, research and support of conservationefforts in the wild. Some zoos and wildlife con-servationists try to manage ecosystems andwildlife populations through research, establish-ing natural preserves, maintaining geneticallydiverse captive-breeding programs, developingeducational programs, and many other activities.Scientists realize that wildlife species cannot be‘saved’ in the long term by protecting themexclusively in zoos. Without sustainable, wildpopulations each species will end up inbred, andwill eventually face extinction.

What should be therole of modern zoos?

These tiger cubs and thisblack-footed ferret (inset)are results of captivebreeding in zoos.

854

Debate the Issue What should be the role ofmodern zoos?

To find out more about modern zoos, visitca.bdol.glencoe.com/biology_society

(t)Steve Kaufman/DRK Photo, (b)David Ulmer/ImageQuest

ca.bdol.glencoe.com/biology_society

0848-0857 C32S2 BDOL-829900 8/4/04 10:33 PM Page 854

Section 32.1

Key Concepts■ Mammals are classified into three

subclasses—placentals, marsupials, and monotremes—based on how theyreproduce.

■ Placental mammals carry younginside the uterus until their bodysystems are fully functional.Nourishment inside the uterusoccurs through an organ called the placenta.

■ Marsupials carry partially devel-oped young in a pouch on theoutside of the mother’s body.

■ Monotremes are egg-layingmammals found only inAustralia, Tasmania, and New Guinea.

Vocabularygestation (p. 848)marsupial (p. 849)monotreme (p. 850)placenta (p. 848)placental mammal

(p. 848)therapsid (p. 851)uterus (p. 848)

STUDY GUIDESTUDY GUIDE

CHAPTER 32 ASSESSMENT 855

To help you reviewmammals, use the OrganizationalStudy Fold on page 841.

Diversity ofMammals

Vocabularydiaphragm (p. 843)gland (p. 842)mammary gland (p. 842)

MammalCharacteristics

Key Concepts■ Mammals are endotherms giving them the

ability to maintain a fairly constant bodytemperature.

■ Hair is present on all mammals at somepoint in their lives.

■ Mammals feed their young frommodified sweat glands called mam-mary glands.

■ Mammals with teethhave different kindsof teeth that areadapted to the typeof food they eat.

■ Highly developedbrains enable mam-mals to learn.

ca.bdol.glencoe.com/vocabulary_puzzlemaker

Section 32.2

(tl)M.C. Chamberlain/DRK Photo; (tr)E. Hanumantha Rao/Photo Researchers; (b)Mickey Gibson/Animals Animals

0848-0857 C32S2 BDOL-829900 8/4/04 10:34 PM Page 855

Review the Chapter 32 vocabulary words listed inthe Study Guide on page 855. Match the wordswith the definitions below.

1. the hollow, muscular organ in which the off-spring of placental mammals develop

2. a mammal that reproduces by laying eggs3. organ that provides food and oxygen to and

removes waste from the young inside theuterus of placental mammals

4. time during which placental mammalsdevelop inside the uterus

5. in mammals, a sheet of muscles located below the lungs that separates the chest cavity from the abdominal cavity

6. Which of the following is NOT a character-istic of mammals?A. endothermicB. three-chambered heartC. hairD. mammary glands

7. Which of these is NOT an endothermicanimal?A. rattlesnake C. catB. penguin D. gorilla

8. Hair helps mammals by providing camou-flage and helping them to maintain________.A. evolution C. reproductionB. running speed D. body temperature

9. ________ are examples of egg-laying mammals.A. Numbats and lemursB. Anteaters and shrewsC. Platypuses and spiny anteatersD. Seals and whales

10. Which pair of terms is most closely related?A. gland—secretionB. diaphragm—heartC. placenta—Golgi bodiesD. gestation—molars

11. Which type of teeth pictured below wouldbe most suited for feeding on grasses?A. C.

B. D.

12. Like bird feathers, mammalian hair probablyevolved from ________.A. teeth C. clawsB. scales D. setae

13. ________ is a behavioral adaptation for cool-ing off a mammal’s body.A. Running C. JoggingB. Panting D. Gnawing

14. Open Ended How does endothermy enablemammals and birds to survive in the Arcticand in the Sahara of Africa?

15. Open Ended Biologists hypothesize that thewhiskers of harbor seals are sensitive to thewakes their prey fish leave behind as theyswim. Design an experiment to test thishypothesis.

16. Concept Map Complete the concept mapby using the following vocabulary terms:marsupials, monotremes, placental mam-mals, placenta.

include

Three groups of

mammals

eggspouch

that have a that lay that have a

1. 2. 3.

4.

856 CHAPTER 32 ASSESSMENT ca.bdol.glencoe.com/chapter_test

0848-0857 C32S2 BDOL-829900 8/4/04 10:35 PM Page 856

Multiple ChoiceThere are only 80–120 wild ocelots left in theUnited States. They are members of the cat familythat require a thorn-scrub habitat. They live insouth Texas, some are protected on the LagunaAtascosa National Wildlife Refuge and the LowerRio Grande Valley National Wildlife Refuge.Examine the map and answer questions 19–21.

19. The best way to improve protection forendangered ocelots would be to ________.A. educate people to the needs of wild ani-

mals and their role in the ecosystemB. have a short hunting seasonC. discontinue agriculture D. capture all ocelots and transport them to

zoos

20. If ocelots disappear from south Texas,________.A. this wild population will rise in the futureB. they can be easily replaced by zoo animalsC. they will be extinct in the United StatesD. their disappearance will not be a problem

for ecosystems since there are so few left

21. Ocelots are found in south Texas ________.A. exclusively on two wildlife refugesB. on wildlife refuges and areas outside the

refugeC. exclusively on South Padre IslandD. only of the seashore of south Texas

Texas

Laguna AtascosaNational Wildlife

Refuge

Lower Rio Grande ValleyNational Wildlife

Refuge

PadreIsland

South PadreIsland

LagunaMadre

Gu

l fo

fM

ex

i co

Documentedocelot

CHAPTER 32 ASSESSMENT 857

ca.bdol.glencoe.com

ca.bdol.glencoe.com/standardized_test

17. There are recovery efforts taking place in the lower 48 states to save the grizzly bear from extinction. In order for this to happen, there must be support by the public for endangered species protection.Visit to investigatethis problem. Prepare a pamphlet that will

educate the public about the grizzly bears’physical appearance, habitat, feedinghabits, winter survival, management andrestoration efforts, encounters with people,and what to do when hiking and campingin grizzly bear country. Present your pam-phlet to your class.

18. Differentiate You find the skeleton of ananimal. What features would indicate that itis a mammal rather than a reptile?

REAL WORLD BIOCHALLENGE

Constructed Response/Grid InRecord your answers on your answer document.

22. Open Ended How does the development of young inside a uterus enable mammals to adapt toenvironments that reptiles cannot?

23. Open Ended Mammals and insects are both considered to be extraordinarily successful animals.Explain the criteria used in both cases that give them this distinction.

0848-0857 C32S2 BDOL-829900 8/4/04 10:35 PM Page 857