What You’ll Learn■ You will compare and contrast

various reptiles and birds.■ You will identify reptile and

bird adaptations that makethese groups successful.

Why It’s ImportantStudying reptiles, the first ani-mals to become independent ofwater, can help you understandthe adaptations required for lifeon land. Birds are unique in thatthey have feathers and wings—adaptations that contribute tobirds living in a wide variety ofhabitats throughout the world.

Reptiles and BirdsReptiles and Birds

Visit to• study the entire chapter

online • access Web Links for more

information and activities onreptiles and birds

• review content with theInteractive Tutor and self-check quizzes

Birds of prey, such as this barnowl, use their keen eyesight tofind their prey. Barn owls arenocturnal hunters of rodents.They are uncommon, but areeasily identified because of theheart-shaped appearance of the face, small dark eyes, andlong legs.

Understandingthe Photo

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Reptiles31.1SECTION PREVIEWObjectivesExplain how reptile adap-tations make them suitedto life on land.Compare the characteris-tics of different groups ofreptiles.

Review Vocabularyembryo: the earliest stage

of growth and develop-ment of both plants andanimals (p. 402)

New Vocabularyamniotic eggJacobson’s organ

reptile from theLatin word repere,meaning “tocrawl”; A reptile isan ectothermic ani-mal with dry skinand amniotic eggs.

Organize Information As you read Chapter 31, list characteristics of reptiles, as well as information about their diversity and origin, behind the appropriate tab.

Fold a vertical sheet of paper from side to side. Make the back edge about 2 cm longer than the front edge.

Turn lengthwise and fold into thirds.

Unfold and cut only the top layer along both folds to make three tabs.

Label your Foldableas shown.

Reptiles Make the following Foldable to help you organizeinformation about reptiles.

STEP 1

STEP 3

STEP 2

STEP 4

Originof Reptiles

What is a reptile?

Diversityof

Reptiles

Reptiles

31.1 REPTILES 817

What is a reptile?At first glance, it may be difficult to determine how a legless snake is

related to a tortoise. Snakes, turtles, alligators, and lizards are anextremely diverse group of animals, yet all share certain traits that placethem in the class Reptilia.

Early reptiles, called the stem reptiles, as shown in Figure 31.1,were the first animals to become adapted to life on land. All reptileshave adaptations that enable them to complete their life cycles entirely

on land. These adaptationsreleased the stem reptilesand other reptiles from theneed to return to swamps,lakes, rivers, ponds, oroceans for reproduction.

Figure 31.1This is an example of an early reptile, called a stem reptile, that was probably an ances-tor of the long-extinct dinosaurs as well as of today’s living reptiles, birds, and mammals.

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Reptiles have scaly skinUnlike the moist, thin skin of

amphibians, reptiles have a dry, thickskin covered with scales. Scaly skin, asshown in Figure 31.2, prevents theloss of body moisture and providesadditional protection from predators.Because gas exchange cannot occurthrough scaly skin, reptiles are de-pendent on lungs as their primaryorgan of gas exchange.

Reptiles reproduce on landMost reptiles reproduce by laying

eggs on land, as shown in Figure 31.3.Some snakes give live birth to well-developed young. Unlike amphibians,reptiles have no aquatic larval stage, soreptile young are not as vulnerable towater-dwelling predators.

Although all of these adaptationsenabled reptiles to live successfully onland, the evolution of the amniotic(am nee AH tihk) egg was the adapta-tion that liberated reptiles from adependence on water for reproduc-tion. An amniotic egg provides nour-ishment to the embryo and containsmembranes that protect it while itdevelops in a terrestrial environment.The egg functions as the embryo’stotal life-support system.

Skeletal changes in reptilesLook again at Figure 31.1. This

early reptile had legs that were placedmore directly under the body ratherthan at right angles to the body as inearly amphibians. This positioning ofthe legs provides greater body supportand makes walking and running onland easier for most reptiles. They havea better chance of catching prey oravoiding other predators. Reptiles thathave legs also have claws that helpthem obtain food and protect them-selves. Additional evolutionary changesin the structure of the jaws and teeth ofearly reptiles allowed them to use otherresources and niches on land.

Some reptiles have four-chambered hearts

Most reptiles, like amphibians,have three-chambered hearts. Somereptiles, notably the crocodilians,have a four-chambered heart thatcompletely separates the supply ofblood with oxygen from blood with-out oxygen. The separation enablesmore oxygen to reach body tissues.This separation is an adaptation thatsupports the higher level of energyuse required by land animals.

Figure 31.2Scales on a reptile’sskin overlap like tileson a roof.

This snake is shedding. Old scaly skin is dis-carded after new skin grows beneath it.Explain How are overlapping scales anadaptation to life on land?

B

The scales of reptiles, unlike theseparate glossy scales of fishes,are made of protein and are part

of the skin itself. The scalesare all connected to

one another byhinges of skin.

A

818(l)Joe McDonald/DRK Photo, (r)Zig Leszczynski/Animals Animals

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31.1 REPTILES 819William Leonard/DRK Photo

Embryo

Albumen

Chorion The chorion (KOR ee ahn) is a membranethat forms around the yolk,allantois, amnion, and embryo.It and the allantois allow gasexchange for respiration.

EE

Egg tooth A reptile hatches by breaking itsshell with the horny tooth on its snout. Thisegg tooth drops off shortly after hatching.

FF

Amnion The amnion (AM nee ahn) is amembrane filled with fluid that surroundsthe developing embryo. The fluid-filledamnion cushions the embryo and preventsdehydration.

AA

Shell The reptile egg is encased ina leathery shell. Most reptiles laytheir eggs in protected placesbeneath sand, earth, gravel, or bark.

BB

Yolk The main food supply for the embryo is the yolk, which is enclosed in a sac that is also attached to the embryo. The clear part of the egg is albumen (al BYEW mun), a source of additional food and waterfor the developing embryo.

CC

Allantois The embryo’snitrogenous wastes are excretedinto the allantois (uh LAN tuhwus), a membranous sac that isassociated with the embryo’sgut. When a reptile hatches, itleaves behind the allantois withits collected wastes.

DD

An Amniotic EggFigure 31.3The evolution of the amniotic egg was a major step in reptil-ian adaptations to land environments. Amniotic eggsenclose the embryo in amniotic fluid, provide a source offood in the yolk, and surround both embryo and food withmembranes and a tough, leathery shell. These structures inthe egg help prevent injury and dehydration of the embryoas it develops on land. Critical Thinking How is the leath-ery covering of a reptile egg more suited to being laiddeep in the sand than a hard-shelled bird egg would be?

Hatchling turtle with egg tooth

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All reptiles have internal fertiliza-tion. In most cases, the eggs are laidafter fertilization and embryosdevelop after eggs are laid. Most rep-tiles lay their eggs under rocks, bark,grasses, or other surface materials, buta few dig holes or collect materials fora nest. Most reptiles provide no carefor hatchlings, but female crocodileshave been observed guarding theirnests from predators.

Reptiles are ectothermsEven though reptiles are different

from amphibians in many ways, theyare similar in one way. Both amphib-ians and reptiles are ectotherms.They depend on an external heatsource and behavior to maintain theirbody temperature within the rangeneeded to perform life functions,such as digestion. In the cool morn-ing, a turtle might pull itself out ofthe pond or swamp and bask on a login the sunlight until noon. Then,when the temperature gets a little too

warm, the turtle may slipback into the cool water.Figure 31.4 shows otherexamples of behavioral ad-justment of body tempera-ture in reptiles.

Because reptiles aredependent on heat fromthe environment, they donot inhabit extremely coldregions. Reptiles are com-mon in temperate andtropical regions, where cli-mates are warm, and in hotdesert climates. Many

species of reptiles become dormantduring cold periods in moderatelycold environments such as in thenorthern United States.

Explain how reptilesregulate body temperature throughbehavior.

How reptiles obtain foodLike other animals, reptiles have

adaptations that enable them to findfood and to sense the world aroundthem. Most turtles and tortoises aretoo slow to be effective predators, butthat doesn’t mean they go hungry.Most are herbivores, and those thatare predators prey on worms andmollusks. Snapping turtles, however,are extremely aggressive, attackingfishes and amphibians, and evenpulling ducklings under water.

Lizards primarily eat insects. Themarine iguana of the GalápagosIslands is one of the few herbivorouslizards, feeding on marine algae. TheKomodo dragon, the largest lizard, isfound on several islands in Indonesia,north of Australia. It is an efficientpredator, sometimes even of humans.Although lizards such as the Komododragon may look slow, they are capa-ble of bursts of speed, which they useto catch their prey.

820 REPTILES AND BIRDS(t)Carmela Leszczynski/Animals Animals, (b)David Boyle/Animals Animals

Figure 31.4Different reptiles regulate their bodytemperatures by a variety of behaviors.

A bearded lizard sunsitself to get warm.

B

A desert horned lizard staysin the shade during thehottest part of a day.

A

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Snakes are also effective predators.Some, like the rattlesnake, have poi-son fangs that they use to subdue orkill their prey. A constrictor wraps itsbody around its prey, tightening itsgrip each time the prey animalexhales. Two predatory reptiles areshown in Figure 31.5.

How reptiles use their sense organs

Reptiles have a variety of senseorgans that help them detect dangeror potential prey. How does a rattle-snake know that you are nearby?

The heads of some snakes, as shownin Figure 31.6A, have heat-sensitiveorgans or pits that enable them todetect tiny variations in air tempera-ture brought about by the presence ofwarm-blooded animals.

Snakes and lizards are equippedwith a keen sense of smell. Have youever seen a snake flick out itstongue? The tongue is picking upmolecules in the air. The snakedraws its tongue back into its mouthand moves it past or inserts it into apitlike structure called Jacobson’sorgan, described in Figure 31.6B.

Figure 31.6Snakes have sense organs that enable them to detect preyor identify substances in their environment.

A pair of heat-sensitive pits below theireyes enable rattlesnakes to detect prey intotal darkness.

A

The Komodo dragon is a predator that cankill animals as large as a deer or even awater buffalo. Adult Komodo dragons canreach a length of more than 3 m.

A

The snapping turtleis common in NorthAmerica. It hasstrong claws and ahooked beak that issharp enough to bitethrough a person’sfingers.

B

Jacobson’s organ

Tongue

Figure 31.5Many reptiles are skillful predators thatobtain prey in a variety of ways.

821

The long, flexible tongues of snakes and lizardspick up molecules in the air and transfer themto the Jacobson’s organ in the roof of the ani-mal’s mouth where special cells identify them.

B

(tl)Michael Dick/Animals Animals, (tr)Joe McDonald/DRK Photo, (b)Michael Fogden/DRK Photo

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Diversity of ReptilesGracefully gliding snakes and

quickly darting lizards are groupedtogether in the order Squamata.Turtles, slowly plodding and carryingheavy shells, belong to the orderChelonia. Basking crocodiles and alligators, classified in the order Croc-odilia, may look clumsy but are surprisingly quick hunters. Tuataras

are lizardlike reptiles. They make upthe fourth order of reptiles,

Rhynochocephalia.

Turtles have shellsTurtles are the only reptiles pro-

tected by a shell made up of two parts.The dorsal part of the shell is the cara-pace, and the ventral part of the shellis the plastron. The vertebrae andexpanded ribs of turtles are fused tothe inside of the carapace. Most tur-tles have a two-layer shell—a hard,bony inner layer and an outer layer ofhorny keratin. In a few species, theshell is a covering made of tough,leathery skin. Most turtles can drawtheir limbs, tail, and head into theirshells for protection against predators.Although turtles have no teeth, theydo have powerful jaws with a beaklikestructure that is used to crush food.

Some turtles are aquatic, and somelive on land. Turtles that live on landare called tortoises. Tortoises foragefor fruit, berries, and insects. Thelargest tortoises in the world, shownin Figure 31.7, are found on theGalápagos Islands off the coast ofEcuador.

Some adult marine turtles swimenormously long distances to lay theireggs. Like salmon, these turtlesreturn from their feeding grounds tothe place where they hatched. Forexample, green turtles travel from thecoast of Brazil to Ascension Island inthe Atlantic Ocean, a distance ofmore than 4000 km.

Crocodiles include the largest living reptiles

In contrast to marine turtles, croc-odiles don’t migrate to reproduce.They may spend their days alter-nately basking in the sun on a river-bank and floating like motionlesslogs. Only their eyes and nostrilsremain above water. Crocodiles canbe identified by their long, slendersnouts, whereas alligators have short,broad snouts. Both animals havepowerful jaws with sharp teeth that

Wildlife Artist/Photographer

I f you are determined andpatient, you can com-

bine your love of natureand your artistic skills intoa career as a wildlife artistor photographer.

Skills for the JobSome wildlife artists/photographers

spend weeks in the wilderness to find subjects for their art.Others draw, paint, or photograph animals in zoos ornature preserves. Becoming an artist or photographerdepends more on your natural abilities than training, butart or photography courses can help strengthen your skills.Many wildlife artists also study biology or zoology so theycan better understand their subjects. It can take yearsbefore artists are able to support themselves by selling theirwork, so many have another job, such as teaching art in ahigh school or college or giving private lessons.

For more careers in related fields, visit

Figure 31.7In the past, sailorskilled Galápagos tor-toises for food. As aresult, their numbersdeclined rapidly.

822

ca.bdol.glencoe.com/careers

(t)Johnny Johnson/DRK Photo, (b)Tom Brakefield/DRK Photo

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can drag prey underwater and hold itthere until it drowns. Another fea-ture that makes these animals effi-cient predators is that, unlike otherreptiles, they can continue to breatheair with their mouths full of food andwater. The American alligator isfound throughout many of the fresh-water habitats of the southeasternUnited States. The American croco-dile can be found only in salt waterand estuarine habitats in southernFlorida. The American alligator canreach a length of 5 m. Other croco-dilians, such as the Nile crocodile ofAfrica, can grow even longer.

Both alligators and crocodiles layeggs in nests on the ground. Unlikeother reptiles, these animals stay closeto their nests and guard them frompredators. Several crocodilian specieshave been observed holding theirnewly hatched offspring gently intheir mouths as they carried them tothe safety of the water.

Explain how croco-diles and alligators reproduce.

Snakes and lizards have diverse forms

Lizards, like the ones shown inFigure 31.8, are found in many typesof habitats throughout the world.Some live on the ground; some bur-row; some live in trees; and some areaquatic. Many are adapted to hot, dryclimates. Although a few species oflizards are limbless, most lizards havefour legs.

Snakes, in contrast to most verte-brates, have no limbs and lack thebones to support limbs. Exceptions arepythons and boas, which retain bonesof the pelvis. The many vertebrae ofsnakes permit fast undulations throughgrass and over rough terrain. Somesnakes even swim and climb trees.

Snakes usually kill their prey in oneof three ways. Remember that con-strictors wrap themselves aroundtheir prey. Common constrictorsinclude boas, pythons, and anacondas.

Venomous snakes use poison to par-alyze or kill their prey. These includerattlesnakes, cobras, and vipers, whichinject poison from venom glands.

31.1 REPTILES 823(l)Fritz Prenzel/Animals Animals, (r)Mike Bacon/Tom Stack & Associates

Geckos aresmall, nocturnallizards. They livein warm climates,such as those ofthe southernUnited States, WestAfrica, and Asia.

A

The Gila monster of the south-western United States andMexico is a poisonous lizard.

B

Figure 31.8Lizards have many struc-tural and physiologicaladaptations that allowthem to live in differenthabitats.

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(t)Michael Fogden/DRK Photo, (b)John Cancalosi/DRK Photo

Most snakes are neither constrictorsnor poisonous. They get food bygrabbing it with their mouths andswallowing it whole. Snakes eatrodents, amphibians, insects, fishes,eggs, and other reptiles, as shown inFigure 31.9.

The fourth order of reptiles,Rhynchocephalia, is represented bytwo living species of tuatara, one ofwhich is shown in Figure 31.10.Tuataras are the only survivors of aprimitive group of reptiles, most ofwhich died out 100 million years ago.

Origins of ReptilesYou may have marveled at dino-

saurs ever since you were very young.These animals were the most numer-ous land vertebrates during theMesozoic Era. Some were the size ofchickens, and others were the largestland dwellers that ever lived. Learnmore about dinosaurs on pages1084–1085 in the Focus On.

The ancestors of snakes and lizardsare traced to a group of early reptiles,called scaly reptiles, that branched offfrom the ancient stem reptiles. Thename “scaly reptiles” may be mislead-ing because it implies that other rep-tiles lacked scales—which is not true.Although the evolutionary history ofturtles is incomplete, scientists havesuggested that they may also bedescendants of stem reptiles. Dino-saurs and crocodiles are the thirdgroup to descend from stem reptiles,as you can see in Figure 31.11.

Although scientists used to thinkthat birds arose as a separate groupfrom this third branch, there is nowmuch fossil evidence that leads biolo-gists to suggest that birds are the liv-ing descendants of the dinosaurs.

Figure 31.9Many poisonous snakes have hollowfangs for injectingvenom. Venom caneither paralyze or killprey immediately.

Figure 31.10Tuataras are found onlyin New Zealand. Theyhave ancestral features,including teeth fused tothe edge of the jaws,and a skull structuresimilar to that of earlyPermian reptiles.

824 REPTILES AND BIRDS

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31.1 REPTILES 825

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

Snakes and Lizards6800 species

Early reptiles

Mammals

First turtles

Dinosaurs

Birds

Turtles250 species

Crocodiles andAlligators25 species

ANIMALS

Understanding Main Ideas1. Explain how the adaptations of early reptiles

enabled these animals to live on land.2. Describe two ways in which turtles protect

themselves.3. Describe how snakes use the Jacobson’s organ for

finding food.4. Analyze the relationship between modern reptiles

and dinosaurs.

Thinking Critically5. Analyze how having a four-chambered heart ben-

efits crocodiles and alligators on a daily basis.

6. Classify Set up a classification key that allowsyou to identify a reptile as a snake, lizard, turtle,or crocodile. For more help, refer to Classify in theSkill Handbook.

SKILL REVIEWSKILL REVIEW

ca.bdol.glencoe.com/self_check_quiz

Figure 31.11The radiation of orders of reptiles shows their relationships.

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31.2SECTION PREVIEWObjectivesExplain how bird adapta-tions make them suited tolife on land.Relate bird adaptations totheir ability to fly.Interpret the phylogenyof birds.

Review Vocabularyphylogeny: evolutionary

history of a speciesbased on comparativerelationships of struc-tures and comparisonsof modern life formswith fossils (p. 452)

New Vocabularyfeathersternumendothermincubate

Fascinating FeathersUsing Prior KnowledgeScientists use both physiologi-cal and structural characteris-tics to divide organisms intodifferent groups. You alreadyknow how fishes, amphibians,and reptiles differ from eachother. Just by looking at abird, you can see thatthere are obvious dif-ferences between birdsand reptiles. Infer What characteristicsdo birds have that makethem different from reptiles?

What is a bird?After conquering the sea and land, vertebrates took to the air, where there

was a huge source of insect food and a refuge from land-dwelling predators.The existence of more than 8600 species of modern birds, class Aves, shows

that flight was a successful adaptation for survival. Birds inhabit avariety of environments around the world, including

Antarctica, deserts, and tropical rain forests.Biologists sometimes refer to birds as feathereddinosaurs. Fossil evidence seems to indicate that

birds have evolved from small, two-leggeddinosaurs called theropods, illustrated inFigure 31.12. Like reptiles, birds haveclawed toes and protein scales on theirfeet. Fertilization is internal and shelledamniotic eggs are produced in bothgroups. Although some birds are flight-less, all birds have feathers and wings.

Birds have feathersA feather, shown in Figure 31.13, is a

lightweight, modified protein scale that pro-vides insulation and enables flight. You may

have seen a bird running its bill or beak through

Birds

Robin

Chickadee

826 REPTILES AND BIRDS

Figure 31.12Most scientists agree that birds evolved from a group ofreptiles called theropod dinosaurs, as shown in this artist’srendition. The skeletons of birds and theropods are similar.

(t)Steve Maslowski/Photo Researchers, (inset)George Robbins

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its feathers while sitting on a treebranch or on the shore of a pond.This process, called preening, keepsthe feathers in good condition forflight. During preening, a bird alsouses its bill or beak to rub oil from agland near the tail onto the feathers.This conditions feathers and helpsthem last longer. You can comparetypes of bird feathers in the MiniLabon this page.

Even with good care, feathers wearout and must be replaced. The shed-ding of old feathers and the growth ofnew ones is called molting. Mostbirds molt in late summer. However,most do not lose their feathers all atonce and are able to fly while they aremolting. Wing and tail feathers areusually lost in pairs so that the birdcan maintain its balance in flight.

Birds have wingsA second adaptation for flight in

birds is the modification of the frontlimbs into wings. Powerful flightmuscles are attached to a large breast-bone called the sternum and to theupper bone of each wing. The ster-num looks like the keel of a sailingboat and is important because it sup-ports the enormous thrust and powerproduced by the muscles as they moveto generate the lift needed for flight.

Flight requires energy Flight requires high levels of

energy. Several factors are involved inmaintaining these high energy levels.First, a bird’s four-chambered, rapidlybeating heart moves oxygenatedblood quickly throughout the body.While sleeping, a chickadee’s heart,for example, beats 500 times aminute. Compare this to an averagehuman heart, which beats 70 times aminute. This efficient circulation sup-plies cells with the oxygen needed toproduce energy.

31.2 BIRDS 827

Figure 31.13A feather’s structure relates to itsfunction.

Fluffy down feathers have no hooksto hold the filaments together.Down feathers act as insulatorsto keep a bird warm.

A

A large bird can have 25 000 or more con-tour feathers with amillion tiny hooks thatinterlock and make thefeathers hold together,making the bird’s bodystreamlined for flight.

B

Compare and ContrastComparing Feathers Birds have different kinds of feathers.Contour feathers used for flightare found on a bird’s body,wings, and tail. Down featherslie under the contour feathersand insulate the body.

Procedure! Examine a contour feather with

a hand lens, and make a sketch ofhow the feather filaments are hookedtogether.

@ Examine a down feather with a hand lens. Draw a diagram of the filaments of the down feather.

# Fan your face with each feather separately. Note how much air is moved past your face by each type of feather.CAUTION: Wash your hands with soap and water after handling animal material.

Analysis1. Explain How does the structure of a contour feather help

a bird fly?2. Explain How does the structure of a down feather keep a

bird warm?3. Infer What accounts for the differences you felt when

fanning with each feather?

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Second, a bird’s respiratory systemsupplies oxygenated air to the lungswhen it inhales as well as when itexhales. A bird’s respiratory systemconsists of lungs and anterior and pos-terior air sacs. You can see the path airfollows in a bird’s respiratory system inFigure 31.14. During inhalation, oxy-genated air passes through the tracheaand into the lungs, where gas exchangeoccurs. Most of the air, however, passesdirectly into the posterior air sacs.When a bird exhales deoxygenated airfrom the lungs, oxygenated air returnsto the lungs from the posterior air sacs.At the next inhalation, deoxygenatedair in the lungs passes into the anteriorair sacs. Finally, at the next exhalation,air passes from the anterior air sacs outof the trachea. Thus, air follows a one-way path in a bird. Find out moreabout bird flight in Figure 31.15.

Birds are endothermsBirds are able to maintain the high

energy levels needed for flightbecause they are endotherms. Anendotherm is an animal that main-tains a nearly constant body tempera-ture that is not dependent on theenvironmental temperature.

Birds have a variety of ways to save or give off their body heat inorder to maintain a nearly constantbody temperature. Feathers reduceheat loss in cold temperatures. Thefeathers fluff up and trap a layer ofair that limits the amount of heatlost. Responses to high temperaturesinclude flattening the feathers andholding the wings away from thebody. Birds also pant to increase res-piratory heat loss.

A major advantage of being endo-thermic is that birds can live in all envi-ronments, from the hot tropics to thefrigid Antarctic. However, birds andother endotherms must eat largeamounts of food to sustain these higherlevels of energy. Find out what kinds offood birds in your area prefer by doingthe MiniLab on page 830.

Describe anendothermic animal.

Reproduction in birdsBirds, like reptiles, reproduce by

internal fertilization and lay amnioticeggs usually inside a nest. Bird eggsare encased in a hard shell, unlike theleathery shell of a reptile. Bird nestsmay be made out of bits of straw andtwigs, may consist of a depressionscratched into the sand, or may beelaborate structures that are added toyearly. Whatever the type of nest,birds do not leave the eggs to hatchon their own. Instead, birds incubateor sit on their eggs to keep themwarm. The eggs are turned periodi-cally so that they develop properly.

828 REPTILES AND BIRDS

Lung

Posteriorair sacs

Anteriorair sacs

Anteriorair sacs

Trachea Key: Breathing cyclesCycle 1

Cycle 2

Inhalation 1Exhalation 2

Inhalation 1Exhalation 2

Figure 31.14Birds require a great deal of oxygen because theirlarge flight muscles expend huge amounts of ATP.Follow the arrows to see how air passes through abird’s respiratory system. Notice that when a birdinhales, inhalation cycles 1 and 2 occur simultaneously.

PhysicalScience

Connection

Newton’s thirdlaw For everyforce applied byan object, there isan equal butopposite forceapplied on theobject. When youswim, you push onthe water as youpull your armsbackward and kickyour feet. Thewater pushes onyou, causing youto move forward.In the same way, abird forces airdownward byflapping its wings.The air in turnpushes the birdupward, enablingit to fly.

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Sternum

Lung

Crop

GizzardIntestine

Male cardinalWingsBirds have a variety of wing shapes and sizes.Some birds have longer, narrower wingsadapted for soaring on updrafts, whereasothers have shorter, broader wings adaptedfor quick, short flights among forest trees.

AA

Hollow bonesThe hollow bones of birdsare strengthened by bonycrosspieces. The sternum is the large breastbone towhich powerful flightmuscles are attached.

BB

BeaksBirds have beaks,sometimes called bills,covered by a proteincalled keratin, but theydo not have teeth.

CC

FlightFigure 31.15Humans have always dreamed of being able to fly. The popu-larity of hang gliding and parachute jumping may reflect thesedreams. For birds, the ability to fly is the result of complexselective pressures that led to the evolution of many adapta-tions. Critical Thinking Although flying is the main form oflocomotion for most birds, not all birds fly all the time.Some birds do not fly at all. What other forms of loco-motion do birds use? Give specific examples.

Air sacsAbout 75 percent of the airinhaled by a bird passes directlyinto the air sacs rather than intothe lungs. When a bird exhales,oxygenated air in the air sacspasses into the lungs. Birdsreceive oxygenated air whenthey breathe in and when theybreathe out.

FF

DigestionThe digestive system of a bird is adapted for dealingwith large quantities of food that must be eaten tomaintain the level of energy necessary for flight.Because birds have no teeth, many swallow smallstones that help to grind up food in the gizzard.

EE

31.2 BIRDS 829

LegsThe legs of birds are made upof mostly skin, bone, andtendons. The feet are adapted to swimming,perching, walking, or catching prey.

DD

Stephen J. Krasemann/DRK Photo

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In some species of birds, both parentstake turns incubating eggs; in others,only one parent does so. Bird eggs aredistinctive, and often the species ofbird can be identified just by thecolor, size, and shape of an egg. Youcan find out more about the adaptivevalue of bird egg shape in the BioLabat the end of this chapter.

Diversity of BirdsUnlike reptiles, which take on a

wide variety of forms from leglesssnakes to shelled turtles, birds are allvery much alike in their basic formand structure. You have no difficultyrecognizing a bird.

In spite of the basic uniformity ofbirds, they do exhibit specific adapta-tions, depending on the environmentin which they live and the food theyeat. As shown in Figure 31.16, ptar-migans have feathered legs and feetthat serve as snowshoes in the winter,making it easier for the birds to walkin the snow. Penguins are flightlessbirds with wings and feet modifiedfor swimming and a body sur-rounded with a thick layer of insulat-ing fat. Large eyes, an acute sense of

Figure 31.16Examine these birds and infer where they live and how theyare adapted to their environments.

Screech owls

Adélie penguins

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Ptarmigan

Compare and ContrastFeeding the Birds In the winter, it may be difficult for some birds to find food, especially if they live in an environment often blanketed with snow. Making a bird feeder and watching birds feed can be anenjoyable activity for you that may save some birds from starvation. If you do begin feeding birds in the winter, continue to feed them until nat-ural food becomes available in the spring.

Procedure! Obtain several large, plastic milk bottles. Cut holes, about

10 cm in diameter, 5 cm from the base on opposite sides ofeach bottle.

@ Place small drainage holes in the bottom of each bottle. Hang the bottles from wires strung through small holes in the neck of each one.

# Place a different kind of seed (sunflower seeds, hulled oats, cracked corn, wheat, thistle, millet) in different bottles. Add new seed when needed. CAUTION: Alwayswash your hands with soap and water immediately afterrefilling the feeders.

$ Use a bird guide to make a list of numbers and kinds of birdsthat frequent each feeder. Note the type of food offered.

Analysis1. Observe What type of seed attracted the largest variety of

bird types?2. Observe Did any birds visit more than one feeder?3. Infer What do you think an ideal bird food would be?

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31.2 BIRDS 831

hearing, and sharp claws make owlswell-adapted, nocturnal predators ableto swoop with absolute precision ontotheir prey.

The shape of a bird’s beak or bill gives clues to the kind of food the bird eats. Hummingbirds, forexample, have long beaks that areused for obtaining nectar from flow-ers. Hawks, like the one shown inFigure 31.17, have curved beaks thatare adapted for tearing apart theirprey. Pelicans have huge bills withpouches that they use as nets for cap-turing fish. The short, stout beak of acardinal is adapted to cracking seeds.

Many bird species are now threat-ened with extinction due to changes intheir habitats. Read the Problem-SolvingLab to learn where birds are endan-gered. Then read the Biology and Societyat the end of this chapter to learn howillegal trade in wildlife threatens birdsand other animals.

(l)To

m B

leds

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to,

(r)M

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ham

berla

in/D

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Pelican

Hawk

Figure 31.17Different species of birds have differentlyshaped beaks. Explain What can the shapeof a bird’s beak reveal about that bird?

Analyze InformationWhere are the most endangered bird species? More than100 bird species have become extinct in the last 400 years.

Solve the ProblemExamine the world map. The key at the bottom right showsthe number of bird species that are currently threatened withextinction. The numbers appearing on the map indicate theactual number of threatened bird species in specific countries.

Thinking Critically1. Use Numbers If 50 species are

threatened, what is the approximate number of bird species in the United States? (Hint: 2.5 percent of the bird species in the U.S. are threatened.)

2. Estimate It is estimated that about 11 percent or 1107 ofthe world’s bird species are threatened. About how manybird species are there in the world?

3. Observe Hawaii, the Philippines, New Zealand, andMadagascar all show the highest percent of threatenedspecies. What common geographical feature do theseareas share?

4. Infer Use the map to support the fact that many areashave a lower number of threatened species and offer anexplanation as to why this is so.

Fewer than 5%5 to 9.9%More than 10%

Hawaii

Madagascar

Percent of threatenedbird species

50

6453 103

9073

104

47 86

Mauritius

New Zealand

Philippines

64

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832 REPTILES AND BIRDS

Woodpeckers,toucans, andhoney guides

383 species

Owls146 species

Archaeopteryx

Theropod dinosaurPenguins18 species

Herons, bitterns,and ibises114 species

Hawks, eagles, and falcons288 species

Swans, geese, and ducks150 species

Perching birds5200 species

Parrots, lories,and cockatoos

340 species

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

ANIMALS

Origins of BirdsCurrent thoughts about bird evo-

lution are illustrated in Figure 31.18.Scientists hypothesize that today’sbirds are derived from an evolution-ary line of dinosaurs that did not

become extinct. Figure 31.19 showsthe earliest known bird in the fossilrecord, Archaeopteryx. At first, scien-tists thought that Archaeopteryx was adirect ancestor of modern birds;however, some paleontologists now

Figure 31.18The radiation of orders of birdsshows their relationships.

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Understanding Main Ideas1. What features of birds enable them to live

on land?

2. Describe how a bird’s respiratory system works,and explain how air sacs improve a bird’s ability toobtain the energy necessary for flight.

3. What is an endotherm? How does being anendotherm have adaptive value for birds that live in polar regions?

4. Analyze the relationship between modern birds and dinosaurs.

Thinking Critically5. Large, flightless birds once were common in areas

that did not have large, carnivorous predators.Many of these birds are now extinct. Form ahypothesis about the evolution and extinction oflarge, flightless birds.

6. Get the Big Picture Make a table that summa-rizes the adaptations birds have that enable themto fly. For more help, refer to Get the Big Picturein the Skill Handbook.

SKILL REVIEWSKILL REVIEW

31.2 BIRDS 833

Archaeopteryx

Caudipteryx zoui

Figure 31.19The fossil bones of Archaeopteryx show that itwas definitely a bird, whereas those ofCaudipteryx zoui indicate that it was a feath-ered theropod dinosaur.

think that it most likely did not giverise to any other bird groups.Archaeopteryx was about the size of acrow and had feathers and wings likea modern bird. But it also had teeth,a long tail, and clawed front toes,much like a reptile.

Fossil finds in China support the idea that birds evolved from atheropod dinosaur. As illustrated inFigure 31.19, it was flightless and ranto capture prey. It was about 1 m talland had feathers similar to those of

modern birds. Scientists hypothesizethat their feathers helped insulate theanimal, or perhaps were adapted forcamouflage or courtship behavior.Most scientists studying the origins ofbirds hypothesize that feathersevolved before flight.

But feathers aren’t the only featuresshared by modern birds and sometheropod dinosaurs. Both also have asternum, a wishbone, shoulder blades,flexible wrists, and three fingers oneach hand.

ca.bdol.glencoe.com/self_check_quiz

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Before YouBegin

Not all bird eggs have thesame shape. An ostrich eggis almost totally round.Chicken eggs are almost a perfect oval on one end.Cliff-dwelling birds, such as the common guillemot(Uria aalge), have eggs thatcome almost to a point onone end. Why the varietyof shapes? Is there anyadaptive benefit to thisvariety of shapes? Couldegg shape be related towhere the bird nests?

Which egg shape is best?

ProblemWhat shape would be best for an egg to reduce the distanceit could roll if pushed from a nest on the ground or a cliff?

HypothesesThere are several hypotheses that you can test. Your hypo-thesis might be that egg shape influences the distance an eggrolls, or that shape determines the tightness of circular rollingpatterns.

ObjectivesIn this BioLab, you will:■ Design an experiment to test your hypotheses.■ Model different egg shapes and egg masses.■ Experiment to test your hypothesis. ■ Draw conclusions based on your experimental data.

Possible Materialsclay table-tennis ballruler golf ballstring balancehard-cooked egg protractor

Safety PrecautionsCAUTION: Always wear goggles in the lab. Never eat any-thing used in the lab.

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

1. Form a hypothesis and decide on a way to test yourgroup’s hypothesis. Keep the list of available materialsin mind as you plan your procedure.

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

PREPARATIONPREPARATION

Matt Meadows

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31.2 BIRDS 835

2. Consider the following questions as you design yourexperiment: How will you incorporate a control? Howmany egg shapes will you test? How will you model youregg shapes? How many trials will you perform? Howmight you keep egg models identical in mass? Where will you start to measure distance rolled?

Check the PlanDiscuss the following points with other group members todecide the final procedure for each of your experiments.1. What is your independent and dependent variable?2. How will you eliminate all other variables?3. What data will you collect? How many trials will

you run?4. Will you need a data table and how might it be

organized?5. Make sure your teacher has approved your experi-

mental plan before you proceed further.6. Record your hypothesis and carry out your

experiments.7. As you clean up after the lab,

make wise choices about the disposal and recycling of labmaterials.

CLEANUP AND DISPOSAL

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Interpret Data Describe your results after testing your hypothesis.2. Conclude Do your data support your hypothesis? Explain using both

quantitative and qualitative observations.3. Identify Variables What were your independent and dependent

variables?4. Conclude In general, how does mass influ-

ence the distance an egg will roll? How doesegg shape influence the distance an egg willroll or the pattern taken when it rolls?

5. Predict Predict why egg shape or mass maybe helpful adaptations when considering the variety of bird habitats.

6. Compare your data to that of other student groups. What revisionscould be made to your hypothesis or experi-ment based on these comparisions?

ERROR ANALYSIS

Knowledge Find out the chemical andphysical nature of bird shells. Find out howand where birds produce a shell.

Web Links To find out more aboutbirds and bird eggs, visitca.bdol.glencoe.com/birds

Chuck Dresner/DRK Photo

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836 REPTILES AND BIRDS

In May 1998, the U.S. Fish and Wildlife Servicewith the assistance of several foreign law

enforcement agencies, broke up an internationalsmuggling ring. Their three-year investigation—code-named Operation Jungle Trade—ended inthe arrest of smugglers operating in a dozencountries. In what illegal products were thesecriminals trafficking? Not diamonds or drugs, butin animals and rare birds.

Species for sale Some people pay large sumsof money for parrots, tropical fishes, monkeys,snakes and lizards to add to their animal collec-tions or to keep as exotic pets whether it is legalor not. Worldwide, millions of illegal wildlifeproducts—from jewelry made from sea turtleshells to snow leopard coats and lizard skinbelts—are bought and sold annually on thewildlife black market.

Unintended backing People can unknowinglysupport the illegal wildlife trade when they buyseashells, coral jewelry, or ivory trinkets that aresold as souvenirs in many countries. Also, buyingfashion accessories made from animal skins canhelp finance illegal wildlife trade.

Many traditional remedies manufactured incertain countries are made with body parts fromthreatened species. Some users of traditionalremedies believe strongly in the power of certainparts of animals or plants to enhance their physi-cal attractiveness or treat health-related condi-tions. The fact that these parts come fromendangered species and are traded on the blackmarket may be unknown to the user.

Government action An international tradeagreement called CITES (the Convention onInternational Trade in Endangered Species ofWild Fauna and Flora) was enacted in July 1975.Its purpose is to ensure that the buying and sell-ing of wild animals and plants do not endangertheir survival. CITES regulates the internationaltrade of about 5 000 animal species and 25 000plant species living or dead, and any part of or

Illegal Wildlife Trade

Analyze the Issue Research one example of anendangered species that is traded illegally. How has thispractice altered the equilibrium of the ecosystem inthat area? What, if anything, is being done to furtherprevent illegal trading of the organism? Present yourfindings to your class as a multimedia presentation.

To find out more about the illegal wildlife trade, visit

(t)Angelina Lax/Photo Researchers, (inset)M. Wendler/Okapia/Photo Researchers

ca.bdol.glencoe.com/biology_society

products made from them. Currently, 160 gov-ernments are members of CITES. Despite thisglobal agreement, the illegal wildlife trade is amultibillion-dollar-a-year business.

Perspectives The illegal wildlife trade is con-tributing to the near extinction of many species,and with every new extinction, Earth’s biodiversityis decreased. Once a species is gone, illegal wildlifetraders turn to a different species to fulfill thedemands of the market. Education, stricter lawsregulating all trade not just international trade, andbetter enforcement of current laws are needed inorder to curtail the booming illegal wildlife trade.

Confiscated productsfrom endangered speciesand a jaguar skin (inset)

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Section 31.1

Section 31.2

Key Concepts■ Reptiles are ectotherms that have dry, scaly

skins; legs under the body; internal fertil-ization; and amniotic eggs. Most reptileshave three-chambered hearts. Some rep-tiles have four-chambered hearts.

■ Present-day reptiles belong to one of fourgroups. Turtles have shells and no teeth.Crocodiles and alligators have streamlinedbodies and powerful, toothed jaws. Lizardshave a variety of adaptations, includinglong bodies, tails, and short limbs. Snakeshave no limbs. Tautaras are lizardlike rep-tiles with some primitive characteristics.

■ The ancestors of present-day reptiles arose from ancient stem reptiles, which were also the ancestors of the dinosaurs.

Vocabularyamniotic egg (p. 818)Jacobson’s organ (p. 821)Reptiles

Vocabularyendotherm (p. 828)feather (p. 826)incubate (p. 828)sternum (p. 827)

Birds

STUDY GUIDESTUDY GUIDE

CHAPTER 31 ASSESSMENT 837(tl)David Boyle/Animals Animals, (tr)Michael Fogden/DRK Photo

To help you review reptiles, use the Organizational StudyFold on page 817.

Key Concepts■ Birds have adaptations for flight including

feathers; a keel-shaped sternum; a four-chambered heart; endothermy; reinforced,hollow bones; a beak; and air sacs.

■ Birds may be derived from a line ofdinosaurs that did not become extinct.

■ Female birds lay hard-shelled, amnioticeggs usually in a nest. Each bird specieshas unique eggs.

■ Adaptations, such as beak shape and modi-fied feet and wings, ensure the survival ofbirds in their specific habitats.

Characteristics of Class Reptilia and Class AvesClass Organisms Characteristics

Snakes, lizards, Dry, scaly skin; ectothermic; four limbs (some limbless); three- or four-Reptilia crocodiles, alligators, chambered heart; internal fertilization; leathery-shelled, amniotic egg

tuataras

AvesCardinals, penguins, Feathers; wings; sternum; flight (most); endothermic; four-chambered

ostriches, owls heart; internal fertilization; hard-shelled, amniotic egg

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Review the Chapter 31 vocabulary words listed inthe Study Guide on page 837. Determine if eachstatement is true or false. If false, replace theunderlined word with the correct vocabulary word.

1. Jacobson’s organ is a sense organ in snakesthat picks up and analyzes airborne chemicals.

2. A feather is a large breastbone that providesa site for muscle attachment.

3. A sternum is a lightweight, modified scalethat provides insulation and enables flight.

4. An endotherm provides nourishment tothe embryo and contains membranes thatprotect it while it develops in a terrestrialenvironment.

5. What function does the amnion perform inan amniotic egg?A. collects the nitrogenous wastes of the embryoB. supplies food to the embryoC. cushions the embryo and prevents dehydrationD. allows gas exchange during respiration

6. Which of the following is NOT an exampleof a reptile?A. turtle C. penguinB. snake D. tuatara

7. Three features that modern-day birds shareare ________.A. endothermy; a three-chambered heart; dry,

scaly skinB. endothermy, feathers, a three-chambered heartC. internal fertilization, amniotic eggs, feathersD. ectothermy, internal fertilization, hard-

shelled eggs8. Three features that modern-day reptiles

share are ________.A. endothermy; a four-chambered heart; and

dry, scaly skinB. endothermy, feathers, a three-chambered heartC. internal fertilization, an amniotic egg, leath-

ery-shelled eggsD. ectothermy, internal fertilization, hard-

shelled eggs that hatch inside the female

9. Concept Map Complete the concept mapby using the following vocabulary terms:sternum, feathers, endotherms.

10. Open Ended Nest temperature determinesthe gender of a reptile embryo. In alligatorsand crocodiles, low nest temperatures pro-duce all female offspring. High nest temper-atures produce all male offspring. Explainhow this phenomenon could affect futurepopulations of species in a particular area.

11. Open Ended Explain how a bird’s circula-tory and respiratory system interrelate toallow birds to achieve flight.

12. Open Ended Why are the fossils ofArchaeopteryx and Caudipteryx zoui significantin explaining the evolutionary history of birds?

13. Predict Most dinosaurs had their center ofmass near the hips, while most modern birdshave their center of mass near the wings.Predict where the center of mass of thero-pod dinosaurs would be.

14. Visitto investigate the rea-

sons for declining numbers of sea turtles.Select one species of sea turtle and design apamphlet that describes your selected turtle,the reasons for decline, and the efforts thatcould be made to protect this species.

REAL WORLD BIOCHALLENGE

838 CHAPTER 31 ASSESSMENT

Birds can live in any environmentbecause they are

1.

2. 3.

flight

and they have adaptations for

such as

two types ofa keeled

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ca.bdol.glencoe.com/chapter_test

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15. Design an Experiment Alligator faces arecovered with small, pigmented domes.Scientists hypothesize that the domes areextremely sensitive to small disturbances onthe water’s surface. Design an experimentthat would test this hypothesis.

16. Infer Bar-headed geese migrate over the topof Mount Everest where oxygen levels areonly one third of what they are at sea level.What parts of bar-headed geese bodiesmight have adaptations to survive in areaswith low levels of oxygen?

CHAPTER 31 ASSESSMENT 839

Ru

nn

ing

sp

eed

Leg length

Running Speed Versus Leg Length in Anole Lizards

017.5

18.0

18.5

19.0

19.5

2 4 6 8 10 12 14

Size

of

each

new

ly h

atch

ed b

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(mas

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gra

ms)

Number of eggs

Relationship Between Nestling Sizeand Number of Eggs

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

20. Open Ended Describe the relationship between the number of eggs laid and the size of a newlyhatched bird for the species described in questions 18 and 19. Explain why this occurs.

21. Open Ended Most reptiles lay between one and 200 eggs at a time. Amphibians lay thousands ofeggs at a time. Is there an adaptive advantage to laying fewer eggs on land?

ca.bdol.glencoe.com/standardized_test

Multiple ChoiceUse the graph below to answer question 17.

17. The relationship between running speed andleg length in anole lizards can best bedescribed as which of the following:A. As leg length increases, running speed

increases.B. As leg length decreases, running speed

increases.C. Leg length and running speed are not

related.D. Running speed decreases as leg length

increases.

Use the graph below to answer questions 18 and 19.

18. If 13 eggs are laid, what is the mass of anewly hatched bird?A. 17.5 gB. 17.6 gC. 18.1 gD. 18.3 g

19. How many eggs were laid if the mass of anewly hatched bird is 18.8 g?A. 5 C. 7B. 6 D. 8

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