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26 A Closer Look at Amniotes

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<strong>26</strong>CHAPTERA <strong>Closer</strong> <strong>Look</strong><strong>at</strong> <strong>Amniotes</strong>KEY CONCEPTS<strong>26</strong>.1 <strong>Amniotes</strong>Reptiles, birds, and mammals are amniotes.<strong>26</strong>.2 ReptilesReptiles were the first amniotes.<strong>26</strong>.3 BirdsBirds have many adapt<strong>at</strong>ions for flight.<strong>26</strong>.4 MammalsEvolutionary adapt<strong>at</strong>ions allowed mammals to succeeddinosaurs as a dominant terrestrial vertebr<strong>at</strong>e.BIOLOGYCLASSZONE.COMBIOLOGYView anim<strong>at</strong>ed chapterconcepts.• Bird Flight• Beak Shape and DietKeep current with biology news.• Fe<strong>at</strong>ured stories• News feeds• CareersRESOURCE CENTERGet more inform<strong>at</strong>ion on• Body Temper<strong>at</strong>ure• Reptiles• Birds786 Unit 8: Animals


Is this a monkeyor a mouse?The large eyes and ears of this easterntarsier make it an excellent nocturnalhunter. These unusual mammals are prim<strong>at</strong>esand are closely rel<strong>at</strong>ed to modernmonkeys. About the same size as a kitten,a tarsier has strong hind legs similar tothose of frogs. The tarsier’s eyes cannotmove but it has a full range of view becauseit can rot<strong>at</strong>e its head almost 360 degrees.ConnectingCONCEPTSBiomes Tarsiers areexceptional climbers th<strong>at</strong>live only in the tropical rainforests of southeastern Asia.Deep within these junglesare areas of the highestbiodiversity on Earth. Highabove the ground, an entirecommunity of species haveadapted to become arboreal.They live almost their entirelives in the treetops, orforest canopy, very rarelysetting foot on the denseforest floor.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 787


<strong>26</strong>.1 <strong>Amniotes</strong>KEY CONCEPT Reptiles, birds, and mammals are amniotes.MAIN IDEAS• Amniote embryos develop in a fluid-filled sac.• An<strong>at</strong>omy and circul<strong>at</strong>ion differ among amniotes.• <strong>Amniotes</strong> can be ectothermic or endothermic.VOCABULARYpulmonary circuit, p. 789systemic circuit, p. 789ectotherm, p. 791endotherm, p. 791Connect When you were about nine weeks into your development, you had amass of about 2 grams and measured about 18 millimeters long, roughly the sizeof a dime. Over the next seven months, you grew and developed while livingsafely inside a fluid-filled membrane, or amniotic sac. There are many differenttypes of amniotes, but each of them, like you, begins life inside an amniotic sac.FIGURE <strong>26</strong>.1 Amniotic EggInside the shell of an amniotic egg, four membranesperform specific functions during development ofthe embryo.embryoAmnion Protectsand surroundsthe embryoChorion Allows gas exchangewith outside environmentMAIN IDEAAmniote embryos develop in a fluid-filled sac.Reptiles, birds, and mammals are all amniotes. Recall from Chapter 25 th<strong>at</strong>amniotes develop in a sac inside the mother’s abdomen. This sac containseverything an embryonic vertebr<strong>at</strong>e needs to grow and prepare for the worldoutside. In some amniotes, the sac is contained inside the mother’s body. Inother amniotes, a tough outer shell protects embryos as they develop outsideof the mother. This shell is semipermeable, which means th<strong>at</strong> it allows gasessuch as oxygen and carbon dioxide to pass through but prevents the embryofrom drying out by holding w<strong>at</strong>er inside.Allantois Holdswaste m<strong>at</strong>erials asthe embryo growsYolk sac Contains thenutrient supply for thegrowing embryoAn egg is a completely self-sustaining containerth<strong>at</strong> provides enough energy and nutrients toenable the embryo to m<strong>at</strong>ure. The illustr<strong>at</strong>ion inFIGURE <strong>26</strong>.1 shows the different membranes foundinside an amniotic egg. The egg you may havee<strong>at</strong>en for breakfast this morning was formed withall of the necessary membranes and nutrient storesto support a chicken embryo. But because the eggwas never fertilized, the genetic composition ofthe egg remained haploid and did not develop intoan embryo.The development of the amniotic egg was animportant adapt<strong>at</strong>ion because it allowed vertebr<strong>at</strong>esto reproduce on land. Without the self-containedsource of energy and w<strong>at</strong>er, an egg needed todevelop in w<strong>at</strong>er or else the embryo would dry out.Predict Wh<strong>at</strong> happens when all of the resources th<strong>at</strong>are stored inside the egg are used?788 Unit 8: Animals


MAIN IDEAAn<strong>at</strong>omy and circul<strong>at</strong>iondiffer among amniotes.Over time, amniotes have evolved manydifferent body shapes and sizes, resultingin many differences in an<strong>at</strong>omy andblood circul<strong>at</strong>ion.An<strong>at</strong>omyThe first amniotes walked in a sprawl similarto th<strong>at</strong> of the lizard in FIGURE <strong>26</strong>.2. A lizard’slegs stick out on either side of its body. Itwalks with its elbows and knees bent.Muscles around the ribs help propel the bodyforward, and their contractions make the lizard’s body sway from side to sidewith each step. Because these same muscles also infl<strong>at</strong>e the lungs, many animalswith a sprawling stance cannot run and bre<strong>at</strong>he <strong>at</strong> the same time. However,some reptiles have adapt<strong>at</strong>ions th<strong>at</strong> allow them to bre<strong>at</strong>he while running.<strong>Amniotes</strong> such as mammals, dinosaurs, and birds evolved a more uprightstance. The c<strong>at</strong> in FIGURE <strong>26</strong>.2 has straighter limbs than the lizard. Its legs areunderne<strong>at</strong>h its body and hold it far away from the ground. When it walks, itslegs swing back and forth like pendulums, and its body does not wiggle fromside to side. An upright stance uses less energy than a sprawling one. It alsosepar<strong>at</strong>es the muscles the animal uses to bre<strong>at</strong>he from the muscles it uses towalk and run. The evolution of the diaphragm, an independent muscle usedto expand the chest cavity and force air into the lungs, separ<strong>at</strong>ed the musclesneeded for walking and bre<strong>at</strong>hing. A diaphragm enables amniotes with anupright stance to run and bre<strong>at</strong>he <strong>at</strong> the same time.Circul<strong>at</strong>ionAs amniotes evolved, their bodies required more energy for movement andgrowth. To get this energy, their tissues demanded more energy and neededhighly efficient ways of delivering this oxygen. This need led to the developmentof many different types of circul<strong>at</strong>ory systems. All amniotes have acentralized heart th<strong>at</strong> moves blood through a complex system of blood vesselsto deliver nutrients to tissues and organs.All amniotes have two circuits of blood vessels. Because the circuits aresepar<strong>at</strong>e, amniotes can conserve energy more effectively. The two circuitsof blood vessels are the pulmonary and systemic circuits.• The pulmonary circuit moves oxygen-poor blood from the heart to thelungs, and oxygen-rich blood back to the heart.• The systemic circuit moves oxygen-rich blood from the heart to the restof the body.The differences in amniote circul<strong>at</strong>ory systems evolved over millions ofyears. As you will see, these differences affect the efficiency of an organism’severyday functions and behavior.FIGURE <strong>26</strong>.2 The sprawling walkingstyle illustr<strong>at</strong>ed by thisKomodo dragon is very differentfrom the upright stance of a c<strong>at</strong>.An<strong>at</strong>omical fe<strong>at</strong>ures make bre<strong>at</strong>hingeasier and more efficient forupright walkers.TAKING NOTESUse a two-column chart to takenotes on the pulmonary andsystemic blood circuits.Pulmonary CircuitSystemic CircuitChapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 789


ConnectingCONCEPTSCircul<strong>at</strong>ory System The heart isa muscle for pumping bloodthrough the body. It is made oftwo different types of chambers.The right and left <strong>at</strong>ria collectblood from the body and lungs,and the right and left ventriclespump blood to the lungs andbody. You will learn more aboutthe heart in Chapter 30.Like amphibians, reptiles have a three-chambered heart. A reptile’s hearthas two <strong>at</strong>ria and one ventricle, as shown in FIGURE <strong>26</strong>.3. One <strong>at</strong>rium collectsoxygen-poor blood from the body. The other collects oxygen-rich blood fromthe lungs. Both <strong>at</strong>ria send blood into the ventricle, which pumps blood intothe pulmonary and systemic circuits. This unique an<strong>at</strong>omy lets these animalstemporarily “turn off” their lungs. Like amphibians, amniotes such as lizardsand turtles do not bre<strong>at</strong>he continuously. Remember th<strong>at</strong> sprawling amniotesstop bre<strong>at</strong>hing when they run. Others spend a lot of time under w<strong>at</strong>er. Ineither case, a single ventricle can divert blood away from the lungs when theanimal is not using them. This str<strong>at</strong>egy lets these animals adjust blood flowin response to their oxygen needs.Mammals and birds have a four-chambered heart. As you can see inFIGURE <strong>26</strong>.3, four-chambered hearts have two <strong>at</strong>ria and two ventricles. Thisan<strong>at</strong>omy keeps oxygen-poor and oxygen-rich blood separ<strong>at</strong>e, but it cannotshift blood away from the lungs when the animal is not bre<strong>at</strong>hing. Keepingoxygen-rich and oxygen-poor blood separ<strong>at</strong>e effectively increases the flow ofoxygen-rich blood to tissues. This adapt<strong>at</strong>ion gives these active animals a largeand constant supply of oxygen. The development of the four-chambered heartallowed for an increase in energy use and eventually gave organisms increasedcontrol over their body temper<strong>at</strong>ure.Infer Many reptiles are ambush pred<strong>at</strong>ors, hiding and waiting for prey to come tothem as opposed to actively hunting. Explain how this behavior may be rel<strong>at</strong>ed totheir circul<strong>at</strong>ory system.FIGURE <strong>26</strong>.3 Amniote HeartsThe heart, the pump th<strong>at</strong> moves blood around an organism’sbody, has developed differently in reptiles and mammals.Oxygen-poor bloodOxygen-rich bloodTHREE-CHAMBERED HEARTReptile hearts have three chambers. A septum th<strong>at</strong> only partiallydivides the heart helps direct oxygen-rich and oxygenpoorblood.to bodyto bodyright<strong>at</strong>riumfrom lungsFOUR-CHAMBERED HEARTBirds and mammals have a heart divided into four chambers,which keeps oxygen-rich and oxygen-poor blood separ<strong>at</strong>e.from bodyto bodyfrom lungsto lungsto lungsleft <strong>at</strong>riumright<strong>at</strong>riumleft <strong>at</strong>riumfrom bodyventricleseptumrightventricleseptumleft ventricleContrast How do differences in the septum affect blood flow in these hearts?790 Unit 8: Animals


MAIN IDEA<strong>Amniotes</strong> can be ectothermic or endothermic.Like all organisms, amniotes are more active when they are warm. Enzymesth<strong>at</strong> speed up the chemical reactions inside cells are more active <strong>at</strong> highertemper<strong>at</strong>ures. A warm amniote digests food faster and can send more nutrientsto its tissues. It can also move faster because its muscles contract morequickly and more often. All living organisms absorb he<strong>at</strong> from the environmentand release he<strong>at</strong> as a byproduct of metabolism. But all animals managehe<strong>at</strong> in different ways.You may have heard the term “cold-blooded” to describe asnake or a lizard. This term does not accur<strong>at</strong>ely describe reptilesand amphibians, because their blood is not actually cold.Instead, scientists use the term ectotherms to refer to organismswhose body temper<strong>at</strong>ures are determined by their surroundingenvironment. These organisms’ body temper<strong>at</strong>ure fluctu<strong>at</strong>eswith the temper<strong>at</strong>ure of their environment. They have higherbody temper<strong>at</strong>ures in a warm environment than in a cool one.Ectotherms regul<strong>at</strong>e their body temper<strong>at</strong>ure through theirbehavior. For example, many reptiles, such as the chameleon inFIGURE <strong>26</strong>.4, bask in sunny places to warm their tissues when theyare cold. Similarly, desert lizards move into shady burrows whenoutside temper<strong>at</strong>ures climb too high. Large animals have aharder time shedding he<strong>at</strong> than small animals. If an ectothermicanimal is massive enough, it will take a long time to cool down.Large ectotherms, such as crocodiles, can stay warm even whenthe environment is rel<strong>at</strong>ively cool.On the other hand, you have probably heard humans andother mammals described as “warm-blooded.” But to describethese organisms more accur<strong>at</strong>ely, scientists use the term endotherm.Endotherms are organisms th<strong>at</strong> use their own metaboliche<strong>at</strong> to keep their tissues warm. More specifically, endothermsregul<strong>at</strong>e their metabolic activity in ways th<strong>at</strong> keep their bodytemper<strong>at</strong>ure rel<strong>at</strong>ively constant all of the time. They may shiverwhen they get too cold, contracting their muscles to gener<strong>at</strong>eextra he<strong>at</strong>. If they get too hot, they may cool down by swe<strong>at</strong>ingor panting. Many endotherms, such as the polar bear inFIGURE <strong>26</strong>.4, are covered with insul<strong>at</strong>ion in the form of hair, f<strong>at</strong>cells, or fe<strong>at</strong>hers, which helps them control he<strong>at</strong> loss.You can think of endotherms and ectotherms as having two differentstr<strong>at</strong>egies for managing energy use. There is a trade-off between an animal’sbody temper<strong>at</strong>ure and the amount of energy it uses. Warm tissues workquickly and require more ATP, which requires an animal to e<strong>at</strong> more. Forexample, lions and crocodiles are both large pred<strong>at</strong>ors, but a crocodile cansurvive on much less me<strong>at</strong> than a lion can. In short, ectotherms are less activewhen it is cold but can survive on less food than endotherms. Endothermsare active all the time but must e<strong>at</strong> more than ectotherms e<strong>at</strong>.FIGURE <strong>26</strong>.4 As an ectotherm,a chameleon increases its bodytemper<strong>at</strong>ure by basking in sunlight.Endotherms such as thispolar bear can maintain a rel<strong>at</strong>ivelyconstant body temper<strong>at</strong>ureeven in cold environments.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 791


DATA ANALYSISCHOOSING GRAPHSChoosing an appropri<strong>at</strong>e type ofgraph to represent d<strong>at</strong>a collected inan experiment is an important partof the scientific process.The table to the right contains d<strong>at</strong><strong>at</strong>h<strong>at</strong> show the differences in energyrequirements for endotherms andectotherms. Despite having similarsizes, endotherms and ectothermsuse energy in different ways andtherefore require different amountsof food.TABLE 1. BODY MASS AND FOOD INTAKEOrganism Mass (kg) Food Intake (kg/yr)Nile crocodile 150 750Grey kangaroo 45 1108Komodo dragon 45 250Koala 8 252Monitor lizard 8 93Source: Nagy, K.A. Nutrition Abstracts and Reviews Series B:71.1. Graph Choose and construct one graph th<strong>at</strong> canrepresent both sets of d<strong>at</strong>a.2. Analyze Explain why there is a difference in energyrequirements between endotherms and ectotherms.The ability to regul<strong>at</strong>e their own temper<strong>at</strong>ure served as an importantfunction in the early stages of endotherm evolution. This adapt<strong>at</strong>ion gaveendotherms a distinct advantage over ectotherms as Earth’s clim<strong>at</strong>e changedmillions of years ago. Because they could stay warm in colder we<strong>at</strong>her, endothermswere able to exploit resources th<strong>at</strong> the ectotherms could not. Manyscientists believe th<strong>at</strong> the ability to regul<strong>at</strong>e their own body temper<strong>at</strong>ureallowed endotherms to survive the c<strong>at</strong>astrophic events th<strong>at</strong> led to theextinction of dinosaurs.Analyze As you move away from Earth’s equ<strong>at</strong>or into colder l<strong>at</strong>itudes, why are therefewer ectotherms and more endotherms?<strong>26</strong>.1 ASSESSMENTREVIEWINGMAIN IDEAS1. How did the development of anamniotic egg allow vertebr<strong>at</strong>es toreproduce on land?2. How does an<strong>at</strong>omy and circul<strong>at</strong>iondiffer among amniotes?3. Wh<strong>at</strong> is the difference between anendotherm and an ectotherm?CRITICAL THINKING4. Infer A 30-gram shrew will die ifit cannot e<strong>at</strong> for a few hours. A30-gram gecko thrives on a fewcrickets every other day. Why mightshrews need food more often?5. Compare Illustr<strong>at</strong>e the p<strong>at</strong>h ofblood through a three-chamberedheart when the animal is bre<strong>at</strong>hing.Show how the p<strong>at</strong>hway changeswhen the animal is not bre<strong>at</strong>hing.ConnectingONLINE QUIZClassZone.comCONCEPTS6. Survivorship When eggs arelaid by a species of reptile orbird, they generally stay in anest th<strong>at</strong> is closely guarded bya mother. How does thisbehavior affect the chancesfor offspring to survive toadulthood? Wh<strong>at</strong> type ofsurvivorship str<strong>at</strong>egy does thisrepresent?792 Unit 8: Animals


<strong>26</strong>.2 ReptilesKEY CONCEPT Reptiles were the first amniotes.MAIN IDEAS• Reptiles are a diverse group of amniotes.• Reptiles have been evolving for millionsof years.• There are four modern groups of reptiles.VOCABULARYreptile, p. 793oviparous, p. 793viviparous, p. 793Connect Basking on the sunny banks of the river, the lizard may look slow, butit has a top speed of almost 20 kilometers per hour, and strong jaws filled withsharp teeth. It is a daunting pred<strong>at</strong>or. The eastern w<strong>at</strong>er dragon may only growto 80 centimeters in length and may never compare to a crocodile as a thre<strong>at</strong> tohumans, but it hunts, kills, and e<strong>at</strong>s its prey in the same way th<strong>at</strong> its largercousins do. Wh<strong>at</strong> makes reptiles unique?VOCABULARYThe name reptile comes fromthe L<strong>at</strong>in word, reptilis, whichmeans “creeping.”FIGURE <strong>26</strong>.5 As a reptile, thiseastern w<strong>at</strong>er dragon must useenergy from sunlight to maintainits body temper<strong>at</strong>ure. From itsperch <strong>at</strong>op a rock, it can alsospot pred<strong>at</strong>ors or look for prey.MAIN IDEAReptiles are a diverse group of amniotes.About 200 million years ago, a mass extinction resulted in the loss of manyof Earth’s plant and animal species. One group of organisms th<strong>at</strong> survived—the reptiles—have thrived for millions of years. Reptiles are ectotherms th<strong>at</strong>are covered with dry scales or pl<strong>at</strong>es and reproduce by laying amniotic eggscovered with a tough outer shell.Unlike amphibians, reptiles produce a completely self-sustaining, amnioticegg th<strong>at</strong> allows an embryonic reptile to develop fully before it is born. Thereare two ways th<strong>at</strong> reptile eggs develop.• Oviparous reptiles deposit their eggs into an external nest, and the eggsdevelop completely independent of the adult reptile.• Viviparous reptiles hold the eggs inside their body through the dur<strong>at</strong>ionof development and give birth to live offspring.The shapes and sizes of modern reptiles vary widely. Some reptiles haveno legs. Other reptiles run swiftly on land or spend much of their time in thew<strong>at</strong>er. The oddly shaped turtles and tortoises carry their homes on their backs.Each reptile group has adapted different fe<strong>at</strong>ures th<strong>at</strong> allow it to be successful.But despite these differences, all reptiles share a few similarities.All living reptiles are ectotherms. Recall th<strong>at</strong> an ectotherm’s body temper<strong>at</strong>urechanges based on the surrounding environment. Similar to the easternw<strong>at</strong>er dragon in FIGURE <strong>26</strong>.5, many reptiles spend a gre<strong>at</strong> deal of time basking,or sunb<strong>at</strong>hing, to absorb energy from sunlight. In addition, reptiles have dryscales or pl<strong>at</strong>es th<strong>at</strong> absorb energy and help contain he<strong>at</strong> needed to maintainnormal body functions.Analyze Wh<strong>at</strong> advantages does a self-sustaining egg give reptiles?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 793


FIGURE <strong>26</strong>.6 Turtles and tortoisesare anapsids. Aside fromthe holes for eyes and nose, thisskull of a modern turtle has notemporal holes.AMNIOTE SKULL TYPESSKULLTYPENUMBER OFHOLESAnapsid 0 turtlesSynapsid 1 mammalsDiapsid 2 birds, lizards,crocodiliansMAIN IDEAReptiles have been evolving for millions of years.Fossil evidence suggests th<strong>at</strong> reptiles began to emerge from the w<strong>at</strong>er duringthe l<strong>at</strong>e Paleozoic era, almost 350 million years ago. They became the dominantvertebr<strong>at</strong>e during the Mesozoic era.Synapsids, Anapsids, and DiapsidsScientists discovered th<strong>at</strong>, over time, amniotes evolved into three differentgroups. This discovery was based on temporal holes th<strong>at</strong> are found onthe sides of the amniote skull.Synapsids Reptiles th<strong>at</strong> had one hole in each temporal region were synapsids.The synapsids eventually gave rise to modern mammals.Anapsids Reptiles th<strong>at</strong> have skulls with no temporal holes are anapsids. Scientistsdo not know why anapsids have no skull holes. Some think th<strong>at</strong> they maystill have the same skull an<strong>at</strong>omy as the first amniotes or th<strong>at</strong> they may havelost skull holes through n<strong>at</strong>ural selection. The anapsids of today are turtles andtortoises, with skulls similar to the one shown in FIGURE <strong>26</strong>.6.Diapsids Reptiles th<strong>at</strong> have two holes in each temporal region, oneabove the other, are diapsids. Diapsid skulls came about as reptilesEXAMPLE began to colonize land. For the next 200 million years, diapsidreptiles ruled Earth. Eventually, this group gave rise to many of themodern reptiles and birds of today.Skull holes may have started out as a weight-reducing adapt<strong>at</strong>ion.Less bone would have made the skull lighter and easier to move andgiven more space for muscle <strong>at</strong>tachments, allowing jaw musclesto get larger. The phylogenetic tree in FIGURE <strong>26</strong>.7 shows how theancient and now extinct groups of reptiles may have evolved.Diversity of Extinct <strong>Amniotes</strong>Pelycosaurs were synapsids th<strong>at</strong> first appeared during the l<strong>at</strong>e Carboniferousperiod. This group included both carnivores and herbivores. Some pelycosaurshad a distinctive “sail-back” made of elong<strong>at</strong>ed vertebral spines. Most pelycosaursdied in a mass extinction 245 million years ago, but some of theirdescendants l<strong>at</strong>er gave rise to the mammals.Ichthyosaurs were some of the first diapsid reptiles. An ichthyosaur’s sleekbody, flipper-shaped limbs, and fleshy dorsal fin were similar to those of themodern day dolphin. Ichthyosaurs swam by be<strong>at</strong>ing their fishlike tails backand forth in the w<strong>at</strong>er, and their peglike teeth suggest th<strong>at</strong> they <strong>at</strong>e fish. Fossilevidence indic<strong>at</strong>es th<strong>at</strong> ichthyosaurs first appeared about 250 million years agoand went extinct about 90 million years ago.Plesiosaurs were some of the strangest prehistoric marine reptiles. They“flew” through the w<strong>at</strong>er like sea lions, using four limbs like elong<strong>at</strong>ed flippers.Some plesiosaurs had small heads and very long necks, which were likely usedto help them c<strong>at</strong>ch fish. Others had short necks and long heads and probablychased down larger prey. Fossils show the plesiosaurs first appeared around220 million years ago and then died out around 80 million years ago.794 Unit 8: Animals


FIGURE <strong>26</strong>.7 Phylogenetic Tree of ReptilesThe diversific<strong>at</strong>ion of ancient reptiles eventually led to the evolution of modern animals.lizards, snakes,mammals turtles and tu<strong>at</strong>aras crocodiliansbirdsMillions ofyears agoCenozoicCretaceousichthyosaursplesiosaurspterosaursdinosaurs50100150Jurassic200TriassicPermianpelycosaurs250300Carboniferousanapsidsdiapsids350synapsidsreptilesAnalyze Are there any diapsid mammals? Explain your answer using the diagram.Dinosaurs were the second gre<strong>at</strong> radi<strong>at</strong>ion of the amniote family. Theyappeared 230 million years ago and were the dominant land vertebr<strong>at</strong>es forthe next 150 million years. Many kinds of dinosaurs evolved during th<strong>at</strong> time.Herbivorous species included huge sauropods, tanklike cer<strong>at</strong>opsians, andduck-billed dinosaurs. They were hunted by carnivorous theropod dinosaurs,which eventually gave rise to birds. All of the nonavian, or walking, dinosaurswent extinct 65 million years ago.Pterosaurs were the first vertebr<strong>at</strong>es to evolve powered flight. Their wingsconsisted of skin supported by an extremely elong<strong>at</strong>ed fourth finger. Theearliest species, from the end of the Triassic, were small animals with longtails. L<strong>at</strong>er species, such as Pteranodon lost their tails and grew as large as smallairplanes. Recent fossils show th<strong>at</strong> pterosaurs may have been covered withhair, suggesting th<strong>at</strong> they were endothermic. They went extinct <strong>at</strong> the endof the Cretaceous along with the dinosaurs.Apply How did the discovery of temporal skull holes help scientists determinephylogeny of amniotes?ConnectingCONCEPTSPhylogeny Recall from Chapter17 th<strong>at</strong> a phylogeny is a type ofevolutionary tree th<strong>at</strong> illustr<strong>at</strong>eshow different species are rel<strong>at</strong>edto each other. The rel<strong>at</strong>ionshipsbetween modern animals andancient reptiles help scientistsunderstand evolution.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 795


MAIN IDEAThere are four modern groups of reptiles.Of all the reptiles th<strong>at</strong> evolved during the Mesozoic era, only four groupsare alive today: turtles, sphenodonts, snakes and lizards, and crocodilians.FIGURE <strong>26</strong>.8 Sea turtles live intropical ocean w<strong>at</strong>ers all over theworld.TurtlesThere are about 200 living species of turtles today. Turtles, tortoises, andterrapins are the only remaining anapsid group of amniotes. The distinctiveshape of a turtle is actually a bony shell th<strong>at</strong> encases the reptile’s body. Thedomed back of a turtle’s shell is called the carapace, while the smooth ventralpart is called the plastron. This shell is covered with tough, fl<strong>at</strong>tened pl<strong>at</strong>esmade of ker<strong>at</strong>in th<strong>at</strong> are fused to the turtle’s rib cage and vertebrae. Manyturtles can pull their head and limbs into the shell for protection.Turtles are toothless and have sharp, horny beaks. Most turtles are omnivorous—theye<strong>at</strong> plants as well as animals. They are found in terrestrial, freshw<strong>at</strong>er,and marine environments. Fully terrestrial turtles are called tortoises.They have high domed shells and thick stumpy limbs. Freshw<strong>at</strong>er turtles havefl<strong>at</strong>ter shells. Some species have lost the bone in their shells to become “softshell” turtles. The sea turtle in FIGURE <strong>26</strong>.8, like most marine turtles, has forelimbsth<strong>at</strong> are large flippers th<strong>at</strong> let it “fly” underw<strong>at</strong>er.FIGURE <strong>26</strong>.9 Snakes and lizardsprotrude a forked tongue to collecttiny molecules out of the air.These molecules are interpretedby the Jacobson’s organ to informthe reptile about its surroundings.braintongueJacobson’sorganSphenodontsThe only living sphenodonts are two species of tu<strong>at</strong>ara th<strong>at</strong> live on a few smallislands off the coast of New Zealand. They are closely rel<strong>at</strong>ed to lizards andsnakes, and look similar to a spiny iguana. Tu<strong>at</strong>aras have primitive characteristics,such as a diapsid skull and an eyespot in the center of their head.Snakes and LizardsSnakes and lizards are very closely rel<strong>at</strong>ed and share a number offe<strong>at</strong>ures. Snakes and lizards all shed their skin <strong>at</strong> regular intervals.They also have flexible skulls th<strong>at</strong> let them capture and swallowprey larger than their head. All snakes and lizards use a highlydeveloped organ th<strong>at</strong> allows them to “taste” the air. As shown inFIGURE <strong>26</strong>.9, when a snake or lizard flicks its forked tongue out ofits mouth, the tongue collects particles out of the air. Particles areinterpreted by a sensory receptor called the Jacobson’s organ,which is found in the top of the reptile’s mouth. This organallows lizards and snakes to loc<strong>at</strong>e prey and avoid pred<strong>at</strong>ors.Most lizards are carnivorous. Small species hunt insects,but large species such as the Komodo dragon prey on mammals.Some species, such as iguanas, are strict herbivores. Snakes are agroup of legless lizards. All snakes are pred<strong>at</strong>ors. Some snakes killtheir prey by constriction, wrapping their body around their preyand squeezing. Others use poisons th<strong>at</strong> are injected into theirprey through modified teeth.796 Unit 8: Animals


FIGURE <strong>26</strong>.10 Reptile An<strong>at</strong>omyThe unique fe<strong>at</strong>ures of reptiles include a three-chambered heartand a single reproductive and excretory opening called a cloaca.brainreproductivelung organovarystomachoviductkidneyuretercloac<strong>at</strong>racheaheartliversmall intestinebladderrectumApply How does reptile an<strong>at</strong>omy prevent the organism fromrunning and bre<strong>at</strong>hing <strong>at</strong> the same time?CrocodiliansThere are 23 species of crocodilians, including allig<strong>at</strong>ors, crocodiles, andcaimans. They are all semiaqu<strong>at</strong>ic pred<strong>at</strong>ors th<strong>at</strong> live in swamps and riversin the tropics and subtropics. They are ambush pred<strong>at</strong>ors, waiting underw<strong>at</strong>erto surprise other animals. Their sprawling resting posture makes them lookslow, but they are capable of lifting up their bodies and running <strong>at</strong> up to27 kilometers per hour (17 mph).Crocodilians are one of two groups of archosaurs th<strong>at</strong> survived the massreptile extinction 65 million years ago. Archosaurs were a large group ofreptiles th<strong>at</strong> included crocodiles, dinosaurs, and modern-day birds. Based onfossil evidence, crocodilians are actually more closely rel<strong>at</strong>ed to birds than theyare to lizards and snakes. Many of the body shapes and structures of ancientcrocodilians are similar to the fe<strong>at</strong>ures of modern crocodilians.Summarize Wh<strong>at</strong> fe<strong>at</strong>ures do all reptiles share?<strong>26</strong>.2 ASSESSMENTREVIEWINGMAIN IDEAS1. How is a viviparous reptile differentfrom an oviparous reptile?2. Wh<strong>at</strong> are the major groups ofextinct reptiles?3. Wh<strong>at</strong> fe<strong>at</strong>ures do modern reptilesshare?CRITICAL THINKING4. Classify You find a fossil of a reptileth<strong>at</strong> has a long neck and four longflippers for limbs. It is in marinesediments. To which group of ancientreptiles could it belong?5. Infer Explain why there are noreptiles found in the Arctic.ConnectingONLINE QUIZClassZone.comCONCEPTS6. Amphibians <strong>Amniotes</strong> emergefrom their shell fully developed.Amphibians must gothrough metamorphosis toreach their adult form. Wh<strong>at</strong> isthe advantage of directdevelopment for amniotes?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 797


<strong>26</strong>.3 BirdsKEY CONCEPT Birds have many adapt<strong>at</strong>ions for flight.MAIN IDEAS• Birds evolved from theropod dinosaurs.• A bird’s body is specialized for flight.• Birds have spread to many ecological niches.VOCABULARYairfoil, p. 799sternum, p. 801air sac, p. 801Connect You may share certain fe<strong>at</strong>ures with your parents or siblings. Perhapsyour eyes are the same color or your nose is the same shape. Certain traits makeit easy to identify your ancestors. Birds have a bit more trouble. Th<strong>at</strong> cardinal <strong>at</strong>your bird feeder would probably be surprised to discover th<strong>at</strong> it is rel<strong>at</strong>ed to aferocious Velociraptor, but birds are the surviving rel<strong>at</strong>ives of those prehistoricanimals. Birds are dinosaurs th<strong>at</strong> evolved powered flight.FIGURE <strong>26</strong>.11 Fossil evidenceof Archaeopteryx shows fe<strong>at</strong>uressuch as fe<strong>at</strong>hers and a beaklikestructure not seen in dinosaurs.Archaeopteryx is an importantlink between dinosaurs andmodern-day birds.MAIN IDEABirds evolved from theropod dinosaurs.Most paleontologists agree th<strong>at</strong> birds are the descendants of one group oftheropod dinosaurs. Theropods were bipedal, or two-legged, dinosaurs th<strong>at</strong>evolved during the Triassic period of the Mesozoic era. Most were carnivorous,and some, such as Allosaurus and Tyrannosaurus, were enormous. Theropodfossils support the hypothesis th<strong>at</strong> these dinosaurs are closely rel<strong>at</strong>ed to birds.They show th<strong>at</strong> birds and many theropods share an<strong>at</strong>omical fe<strong>at</strong>ures, including• hollow bones• fused collarbones th<strong>at</strong> form a V-shaped wishbone, or furcula• rearranged muscles in the hips and legs th<strong>at</strong> improve bipedal movement• “hands” th<strong>at</strong> have lost their fourth and fifth fingers• fe<strong>at</strong>hersIn the 1990s scientists discovered theropod fossils with fe<strong>at</strong>hers. Thisimportant discovery showed th<strong>at</strong> fe<strong>at</strong>hers did not origin<strong>at</strong>e as an adapt<strong>at</strong>ionfor flight. These theropods were covered with fe<strong>at</strong>hers, but they did not havewings. They were running animals. This means th<strong>at</strong> fe<strong>at</strong>hers originally hadanother function in the theropods. They may have been insul<strong>at</strong>ion th<strong>at</strong>trapped air to keep the animals warm. Or they may have been used in courtshipor territorial displays. As birds evolved, they used the fe<strong>at</strong>hers they hadinherited from their theropod ancestors to form wings.The oldest undisputed fossil bird is shown in FIGURE <strong>26</strong>.11. Archaeopteryxwas a chicken-sized animal th<strong>at</strong> lived about 150 million years ago. Like allmodern birds, it had fe<strong>at</strong>hered wings and a furcula. But it also had manyreptilian fe<strong>at</strong>ures, including clawed fingers, a long tail, and teeth. Because ofits fe<strong>at</strong>ures, Archaeopteryx was classified as a dinosaur. However, its fe<strong>at</strong>hersmade it an important link between flightless dinosaurs and avian, or flying,dinosaurs, as well as the birds of today.798 Unit 8: Animals


Scientists have two hypotheses for the originof flight in birds. The “trees-down” hypothesissuggests th<strong>at</strong> birds evolved from animals th<strong>at</strong> usedtheir fe<strong>at</strong>hers to glide down to the forest floor. Incontrast, the “ground-up” hypothesis suggests th<strong>at</strong>birds evolved from running animals th<strong>at</strong> usedtheir fe<strong>at</strong>hered arms for balance.The fossil evidence showing a close rel<strong>at</strong>ionshipbetween theropods and birds tends to supportthe “ground-up” hypothesis. Many theropodswere bipedal carnivores th<strong>at</strong> hunted by runningdown their prey. Scientists still do not know howthese dinosaurs moved from running and grabbingto flapping and flying. Some recent researchsuggests th<strong>at</strong> small theropods could have flappedtheir fe<strong>at</strong>hered arms to run up trees and escapepred<strong>at</strong>ors. Whether they also used those fe<strong>at</strong>hered arms to glide back down tothe ground is unknown, but future fossil discoveries may provide an answer.Infer How might hollow bones have helped theropods move more efficiently?FIGURE <strong>26</strong>.12 The broad wings ofan eagle owl are adapted for silentflight, making this nocturnal bird aquiet and deadly pred<strong>at</strong>or.MAIN IDEAA bird’s body is specialized for flight.Birds such as the eagle owl in FIGURE <strong>26</strong>.12 have many specialized adapt<strong>at</strong>ionsfor powered flight. Some of them are modific<strong>at</strong>ions of fe<strong>at</strong>ures inheritedfrom their theropod ancestors. Others are unique to birds. These adapt<strong>at</strong>ionsinclude• wings th<strong>at</strong> produce flight• strong flight muscles th<strong>at</strong> move the wings• an active metabolism th<strong>at</strong> provides energy to the muscles• hollow bone structure th<strong>at</strong> minimizes weight• reproductive adapt<strong>at</strong>ionsWingsWings are structures th<strong>at</strong> enable birdsto fly. Bird wings are curved similar tothe shape of an airplane wing. Thiskind of curved surface is called anVISUAL VOCABAn airfoil is convex on the top andconcave on the bottom. Differencesin air pressure above and below theairfoil cre<strong>at</strong>e lift.airfoil. An airfoil is curved down onthe top (convex) and curved up onthe bottom (concave). The curvedshape makes air move faster over thetop of the airfoil than underne<strong>at</strong>h it.The difference in air speed above and below the airfoil produces a pressuredifference th<strong>at</strong> lifts the wing up. In birds, the airfoil is constructed of limbsth<strong>at</strong> are homologous to human arms and covered by large fe<strong>at</strong>hers.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 799


FIGURE <strong>26</strong>.13 Bird An<strong>at</strong>omyBird an<strong>at</strong>omy is highly adapted, with unique fe<strong>at</strong>uresth<strong>at</strong> help to conserve energy and allow flight.BIOLOGYSee bird flightin action <strong>at</strong>ClassZone.com.FEATHERSFe<strong>at</strong>hers are complex branching structuresmade of ker<strong>at</strong>in. Not only are fe<strong>at</strong>hersimportant for flight but they also provideinsul<strong>at</strong>ion th<strong>at</strong> helps maintain body temper<strong>at</strong>ureand protect the bird’s skin.Fe<strong>at</strong>hers can be shed and replaced if theyare damaged.barbbarbulelunggizzardcropkidneypectoral musclesternum(keel)heartliversmall intestinelarge intestinecloacaHOLLOW BONESstrutThe strut system found in the bonestructure of birds reduces weight withoutcompromising strength. Unlike otheramniotes, birds have bones th<strong>at</strong> are hollowand are directly connected to thebird’s respir<strong>at</strong>ory system.CRITICALVIEWINGA few species of birds do not actually fly. How might the unique fe<strong>at</strong>ures ofbirds be beneficial for penguins, which spend most of their time in w<strong>at</strong>er?800 Unit 8: Animals


MusclesA bird’s chest muscles provide the power for flight. In almost all vertebr<strong>at</strong>es,chest muscles <strong>at</strong>tach to the arms and the breastbone, or sternum. But anyonewho has carved a chicken knows th<strong>at</strong> a bird’s chest muscles are enormous.They are so large th<strong>at</strong> the sternum has evolved a large keel, or ridge, th<strong>at</strong>supports the muscles. The keel provides a large <strong>at</strong>tachment surface for the chestmuscles, and serves as an anchor th<strong>at</strong> they can pull against to flap the wings.When birds fly, their chest muscles contract to pull their wings backwardand down. The downstroke moves the wings to produce lift and propel theanimal forward. Deeper chest muscles contract during the upstroke, movingthe wings forward and up until the bird starts another downstroke.MetabolismFlying takes a lot of energy. Birds are endotherms and have active metabolismsth<strong>at</strong> can produce large amounts of ATP for the flight muscles. But maintainingan active metabolism during flight requires an enormous amount ofoxygen. Birds meet this challenge with a respir<strong>at</strong>ory system th<strong>at</strong> increases theamount of oxygen they can take out of the air.A bird’s body is filled with a series of air sacs AIR SACth<strong>at</strong> connect to the lungs. Air sacs store air astrache<strong>at</strong>he bird bre<strong>at</strong>hes. During flight, movementslungsof the furcula help push air through the air sacs air sacand lungs. Inhaled air travels through the lungsand air sacs in such a way th<strong>at</strong> oxygen-rich airis always available. In other vertebr<strong>at</strong>es, oxygenrichair mixes with oxygen-poor air inside thelungs during respir<strong>at</strong>ion. But because onlyoxygen-rich air flows through a bird’s lungs,the amount of oxygen th<strong>at</strong> can be absorbedinto the bloodstream is dram<strong>at</strong>ically increasedand maximizes a bird’s metabolism.TAKING NOTESUse a main idea diagram to takenotes on how the fe<strong>at</strong>ures ofbirds help them to achieveflight.adapt<strong>at</strong>ions for flightConnectingCONCEPTSCellular Respir<strong>at</strong>ion Birds requirelarge amounts of ATP to providethe energy needed for flight.Recall from Chapter 4 th<strong>at</strong>cellular respir<strong>at</strong>ion needs oxygenand glucose to produce ATP.Air sacs provide a gre<strong>at</strong> deal ofoxygen, but birds must also consumelarge amounts of food tosupport their active metabolism.Bone StructureThe structure of a bird’s skeletal system is different than th<strong>at</strong> of other amniotes.Birds have evolved bones th<strong>at</strong> are hollow. As you can see in FIGURE <strong>26</strong>.13,inside bird bones, a system of struts and support structures maintain thebird’s bones to meet the demanding requirements of flight. In all birds, manybones are connected to the air sacs, and air fills the cavities in the bone, aidingin flight. This adaption further increases the amount of air in a bird’s body,and makes flying easier. It also helps to decrease the mass of the bird. In fact, abird’s skeleton makes up only five percent of its overall body mass.Reproductive Adapt<strong>at</strong>ionsThe reproductive organs of both male and female birds are only active for thetwo to three months of the m<strong>at</strong>ing season. During the rest of the year, theunused organs shrink to reduce the mass of the bird. This weight-reducingadapt<strong>at</strong>ion serves to decrease the amount of energy needed for flight.Summarize How are bird bodies adapted to flying?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 801


QUICK LABOBSERVINGComparing Fe<strong>at</strong>hersFe<strong>at</strong>hers are fe<strong>at</strong>ures th<strong>at</strong> allow birds to adapt to a unique way of life. In this lab, you willexamine three different types of fe<strong>at</strong>hers.SKILL ObservingPROBLEM How do the structures and functions of different fe<strong>at</strong>hers compare?PROCEDURE1. Obtain a large quill fe<strong>at</strong>her and study its overall shape, structure and weight. Drawthe fe<strong>at</strong>ures.2. Examine the central shaft of the fe<strong>at</strong>her. Hold the end of the shaft with one hand.With your other hand, gently try to bend the upper third of the fe<strong>at</strong>her withoutbreaking it.3. Observe the vane, the fl<strong>at</strong> part of the fe<strong>at</strong>her on either side of the shaft. Separ<strong>at</strong>esome of the barbs of a vane. Join them again with your fingers.4. Hold the end of the shaft and wave the fe<strong>at</strong>her so th<strong>at</strong> it c<strong>at</strong>ches the air. Note theresistance you feel as you move the fe<strong>at</strong>her through the air.5. Repe<strong>at</strong> steps 1–4 with the contour and down fe<strong>at</strong>hers.ANALYZE AND CONCLUDE1. Analyze Wh<strong>at</strong> is the function of the shaft?2. Analyze How are down fe<strong>at</strong>hers different from contour and quill fe<strong>at</strong>hers?3. Infer Describe the function of each type of fe<strong>at</strong>her.4. Apply Wh<strong>at</strong> characteristics make quill fe<strong>at</strong>hers well suited for their function?5. Apply How are contour fe<strong>at</strong>hers designed to make a bird streamlined?6. Infer How do you think the structure of down fe<strong>at</strong>hers helps to insul<strong>at</strong>e a bird?MATERIALS• purchased quill fe<strong>at</strong>her• purchased contour fe<strong>at</strong>her• purchased down fe<strong>at</strong>herMAIN IDEABirds have spread to many ecological niches.Birds first evolved during the Mesozoic era, but most Mesozoic bird specieswent extinct with the dinosaurs. All modern birds are the descendants of theone group th<strong>at</strong> survived the mass extinction. This group diversified into themore than 9000 species of bird we see today. Through n<strong>at</strong>ural selection, birdshave adapted to many different habit<strong>at</strong>s and methods of feeding. This has ledto visible physical differences in the shapes of the wings, beaks, and feet.Differences in Wing ShapeThe shape of a bird’s wing reflects the way it flies. Most birds have short, broadwings th<strong>at</strong> allow them to maneuver very easily. In contrast, alb<strong>at</strong>rosses andgulls, such as the blue-footed booby in FIGURE <strong>26</strong>.14, have long, narrow wingsspecialized for soaring long distances over w<strong>at</strong>er. Hawks, eagles, and condorshave wide, broad wings specialized for soaring <strong>at</strong> low speeds over land. Manytypes of songbirds, including woodpeckers, finches, and robins, have stout,tapered wings th<strong>at</strong> help them to maneuver through tight spaces. Penguinshave short wings adapted to “fly” in w<strong>at</strong>er. Flightless birds, such as ostrichesand emus, have wings th<strong>at</strong> are too small to let them fly <strong>at</strong> all.802 Unit 8: Animals


Differences in Beak ShapeThe shape of a bird’s beak reflects how it e<strong>at</strong>s. A bird’sbeak is a she<strong>at</strong>h of ker<strong>at</strong>in th<strong>at</strong> covers the jaw bones. AsCharles Darwin observed in the many finch species ofthe Galapagos Islands, beak shapes are adapted for manydifferent functions. For example, the blue-footed boobyuses its long, spearlike beak to capture fish on the bird’sdives into the ocean. The beak of the bald eagle ishooked to tear flesh from its prey. Birds th<strong>at</strong> c<strong>at</strong>chinsects often have thin, pointed bills. Woodpeckers havebeaks like chisels to pry insects out of trees. Other birds,such as hummingbirds, have long, thin beaks th<strong>at</strong> canreach deep into flowers for nectar. Pelicans have largepouches of skin <strong>at</strong>tached to their beaks for scooping fishout of the w<strong>at</strong>er. Parrots use their thick, strong beaks forripping open fruits and cracking nuts.Differences in Foot ShapeWith few exceptions, bird feet have four toes. But asFIGURE <strong>26</strong>.14 shows, their feet can look very different.The blue-footed booby and other aqu<strong>at</strong>ic birds havewebbed feet, with skin connecting the toes to formpaddles. Pred<strong>at</strong>ory birds such as the bald eagle haveheavy claws th<strong>at</strong> they use to capture and kill prey. Birdsth<strong>at</strong> live in trees have feet th<strong>at</strong> can grab onto branchesand tree bark. Woodpeckers, for example, have two toespointing forward and two pointing backward, which letsthem cling to vertical tree trunks. Sparrows and crowshave three toes pointing forward and one pointingbackward, which lets them perch on horizontal tree limbs.Infer Where would you expect to find a bird with webbed feetand very long and narrow wings?blue-footed boobybald eaglegreen woodpeckerFIGURE <strong>26</strong>.14 Birds’ fe<strong>at</strong>uresare specifically adapted to theirhabit<strong>at</strong> and niche. N<strong>at</strong>ural selectionhas led to a wide array ofwings, beaks, and feet.<strong>26</strong>.3 ASSESSMENTONLINE QUIZClassZone.comREVIEWINGMAIN IDEAS1. Wh<strong>at</strong> are three an<strong>at</strong>omical fe<strong>at</strong>uresth<strong>at</strong> birds share with their theropodancestors?2. Wh<strong>at</strong> adapt<strong>at</strong>ions do birds haveth<strong>at</strong> help them with flight?3. Describe how the wings, beak, andfeet of an eagle are well adapted toits niche.CRITICAL THINKING4. Analyze The red-headed woodpeckerhas an unusually long tongueand a stout, pointed beak. How arethese fe<strong>at</strong>ures rel<strong>at</strong>ed to thewoodpecker’s feeding habits?5. Connect Reptiles and birds areclosely rel<strong>at</strong>ed. Why is the evolutionfrom being an ectotherm tobeing an endotherm so importantfor bird evolution?ConnectingCONCEPTS6. Selection Male cardinals havebright red fe<strong>at</strong>hers, whereasfemales have dull brownfe<strong>at</strong>hers. Wh<strong>at</strong> type of selectionlikely caused thesedifferences?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 803


CHAPTER <strong>26</strong>MATERIALS• balance• 100 mL gradu<strong>at</strong>edcylinder• 50 mL w<strong>at</strong>er• boiled chicken bone(flightless bird)• boiled duck or turkeybone (flying bird)• boiled cow bone(mammal)• hammer• hand lensPROCESS SKILLS• Observing• Measuring• AnalyzingINVESTIGATIONA Bird’s AirframeWings were an important adapt<strong>at</strong>ion for birds. The structure of wings gave birdsthe ability to fly and move gre<strong>at</strong> distances in search of resources. But for somebirds, flight was not necessary for survival. In this lab, you will investig<strong>at</strong>e thedifferences and similarities between flying and flightless birds, and compare themwith mammals.PROBLEM Besides wings, wh<strong>at</strong> major adapt<strong>at</strong>ion is beneficial for flight?PROCEDURE1. Measure the mass of each bone (chicken, duck, cow) using the balance.Record the mass for each.2. Pour the w<strong>at</strong>er in the gradu<strong>at</strong>ed cylinder and note the volume. Add oneof the bones to the cylinder and record the volume again. To find thevolume of the bone, subtract the original volume from the second reading.3. Repe<strong>at</strong> step 2 for each bone used.4. Attempt to break the bone by hand and note how easy or difficult it is.(If you can’t break the bone by hand, it is okay.)Caution: Wearing your safety goggles, carefully breakeach experimental bone with the hammer (w<strong>at</strong>ch out forflying pieces).5. Examine the internal structure of each bone with thehand lens. Make a labeled drawing for each bone.ANALYZE AND CONCLUDE1. Predict Which bone do you think has the gre<strong>at</strong>estdensity? Which bone is the least dense?2. Calcul<strong>at</strong>e Calcul<strong>at</strong>e the densities for each bone(density = _____ massvolume ).3. Apply Wh<strong>at</strong> can you conclude about bone density andthe ability to fly?4. Observe How does the structure of the flightless birdbone compare with th<strong>at</strong> of the flying bird bone? withthe cow bone?5. Infer Wh<strong>at</strong> bones are easier to break by hand thanothers? Explain why you think this is true.6. Analyze Wh<strong>at</strong> fe<strong>at</strong>ures of the bird bones might beadapt<strong>at</strong>ions for flight?7. Contrast Were there any significant differencesbetween bones from flying birds and those fromflightless birds? Why might one bird be able to flywhile another cannot fly?100 mL gradu<strong>at</strong>ed cylinder804 Unit 8: Animals


<strong>26</strong>.4 MammalsKEY CONCEPT Evolutionary adapt<strong>at</strong>ions allowed mammals to succeed dinosaurs as a dominantterrestrial vertebr<strong>at</strong>e.MAIN IDEAS• All mammals share several commoncharacteristics.• Modern mammals are divided into threemain groups.VOCABULARYmammal, p. 805mammary gland, p. 806monotreme, p. 807marsupial, p. 808eutherian, p. 809Connect Each time you get your hair cut, you are having a fe<strong>at</strong>ure clipped offth<strong>at</strong> sets humans and other mammals apart from reptiles, birds, amphibians, andfish. In addition to hair, wh<strong>at</strong> other traits make mammals unique?FIGURE <strong>26</strong>.15 This Yuma myotisb<strong>at</strong> has all of the basic mammalianfe<strong>at</strong>ures. B<strong>at</strong>s are the only mammalsth<strong>at</strong> can fly.MAIN IDEAAll mammals share several commoncharacteristics.All mammals are active, large-brained, endothermic animals with complexsocial, feeding, and reproductive behaviors. Modern mammals—such as theb<strong>at</strong> in FIGURE <strong>26</strong>.15—come in many shapes, but they share a set of four an<strong>at</strong>omicalcharacteristics.• hair• mammary glands• a middle ear containing three bones• a jaw th<strong>at</strong> lets them chew their foodMammals are as ancient as dinosaurs and are the only group of synapsidsalive today. They are descended from a group of carnivorous synapsids. Manyof the characteristics we now see only in mammals were actually inheritedfrom these reptilian ancestors. Earth’s first mammals appearedmore than 200 million years ago, when dinosaurs were alreadyon their way to becoming the top pred<strong>at</strong>ors and herbivores onthe planet. During the Cretaceous period, while Tyrannosaurusrex was hunting Tricer<strong>at</strong>ops, tiny rodentlike mammals hadfound a niche as nocturnal insect e<strong>at</strong>ers.Fossil evidence suggests th<strong>at</strong> early mammals had longnoses and short legs. They may have looked similar to moderndayshrews. They probably lived underground, reproduced by layingeggs, and nursed their young on nutrient-rich milk produced byhighly adapted glands. The ability to regul<strong>at</strong>e their own bodytemper<strong>at</strong>ure was an important adapt<strong>at</strong>ion th<strong>at</strong> gave mammals adistinct advantage over reptiles. When the dinosaurs went extinct,mammals survived and filled their vacant ecological niches. In time,mammals succeeded dinosaurs as a dominant terrestrial life form.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 805


ConnectingCONCEPTSN<strong>at</strong>ural Selection All mammalshave hair or, more accur<strong>at</strong>ely, hairfollicles. Whales are mammals,but most adult whales do nothave hair. Recall from Chapter 10th<strong>at</strong> n<strong>at</strong>ural selection favorstraits th<strong>at</strong> increase the fitnessof individuals. In the underw<strong>at</strong>erenvironment of whales, haircauses resistance and may beobstructions in c<strong>at</strong>ching prey,thus making them less likely tosurvive and reproduce.FIGURE <strong>26</strong>.16 Mammals producemilk in mammary glands to providenutrients to their offspring.These piglets will nurse from theirmother for three to eight weeks.HairMammals are furry. Most species are covered with a layer of hair th<strong>at</strong> helpsthem retain he<strong>at</strong>. Each hair is a long, thin shaft of dead, ker<strong>at</strong>inized cells th<strong>at</strong>grows out of a follicle in the skin. The hair traps a layer of air next to the skin,which insul<strong>at</strong>es the animal, much like a down vest insul<strong>at</strong>es you. When mammalsget cold, muscles around the follicles pull the hair upright. When you get“goose bumps,” your insul<strong>at</strong>ing air layer is thickening to help keep you warm.Hair also has other functions. Anyone who has w<strong>at</strong>ched a frightened c<strong>at</strong>fluff up knows th<strong>at</strong> mammals can use hair for behavioral displays. P<strong>at</strong>ternsof pigmented hairs provide camouflage for many mammals. Porcupines andhedgehogs have modified hairs th<strong>at</strong> form stiff protective quills. And manymammals have long, stiff whiskers th<strong>at</strong> collect sensory inform<strong>at</strong>ion. Evenmammals th<strong>at</strong> have lost most of their hair, such as whales, retain somesensory bristles.Mammary GlandsAll mammals take care of their babies after they are born.Females feed them a specialized fluid called milk.Mammary glands are specialized glands th<strong>at</strong> produce milk.Milk contains w<strong>at</strong>er, sugars, protein, f<strong>at</strong>s, minerals, andantibodies th<strong>at</strong> help young animals grow and develop.Mammary glands are unique to mammals. They arepresent in both males and females but produce milk only infemales. Some mammals, such as pigs or dogs, have a seriesof glands along the belly. Other mammals have glands onlyin specific areas, such as udders in a cow’s groin or the pairof glands on a prim<strong>at</strong>e’s chest. Mammary glands containmasses of milk-producing tissues th<strong>at</strong> are connected to aseries of ducts. The ducts bring milk to the surface of theskin. In most mammals, the ducts empty into nipples orte<strong>at</strong>s th<strong>at</strong> young mammals, such as the piglets inFIGURE <strong>26</strong>.16, can hold in the mouth and suckle.Middle EarMammals have three small bones in their middle ear. One of the bones, thestapes, is also found in other tetrapods. The other two, the malleus and incus,are unique to mammals. They were derived from reptilian jaw bones.The top part of the hyoid arch became modified to form the stapes in earlytetrapods. Bones th<strong>at</strong> supported the jaws in fish became bones th<strong>at</strong> transferredvibr<strong>at</strong>ions to the inner ear in tetrapods. A similar shift, illustr<strong>at</strong>ed inFIGURE <strong>26</strong>.17, occurred as mammals evolved from their reptilian ancestors.Synapsids such as the pelycosaur had jaws th<strong>at</strong> were made of many bonesfused together. The middle ear of these reptiles contained only one bone, thestapes, which transmitted sound to the inner ear, where it was converted tonerve impulses and interpreted by the brain. This is the same configur<strong>at</strong>ion ofbones we see in reptiles today.806 Unit 8: Animals


Over time, the form<strong>at</strong>ion of these bones changed.Two bones, the quadr<strong>at</strong>e and the articular bones,once formed the joint between the jaws of reptiles.These bones evolved to serve a different function—hearing. In mammals, the quadr<strong>at</strong>e and articularbones are now tiny and are incorpor<strong>at</strong>ed into themiddle ear as the malleus and the incus. Soundscollected in the ear canal vibr<strong>at</strong>e the eardrum. Thesevibr<strong>at</strong>ions are transferred through the malleus andincus bones to the stapes. These tiny vibr<strong>at</strong>ions areconverted into nerve impulses in the inner ear andthen interpreted by the brain. The ability to detectsmall vibr<strong>at</strong>ions allowed mammals to hear higherpitchedsounds.ChewingMammals developed the ability to chew their food.Amphibians, reptiles, and birds usually bite off largechunks of food or swallow it whole. Most of theirmechanical processing occurs inside their digestivetract. Mammals, in contrast, start to break up theirfood as soon as it enters the mouth.REPTILIAN EAR BONEeardrum inner earmiddle earstapesMAMMALIAN EAR BONESeardruminner earmalleusincusA set of adapt<strong>at</strong>ions in the mammalian jawmakes chewing possible. While food is in the mouth,ear canal stapesa secondary pal<strong>at</strong>e separ<strong>at</strong>es the nasal and oralcavities. It keeps the passages for air and food separ<strong>at</strong>e, so mammals can chewand bre<strong>at</strong>he <strong>at</strong> the same time. In addition, complex muscles can move the jawfrom side to side.Infer Hair was an important adapt<strong>at</strong>ion for mammals. How might hair and otheradapt<strong>at</strong>ions have enabled mammals to survive where reptiles could not?FIGURE <strong>26</strong>.17 As mammalsevolved, the structures of theinner ear changed. The incusand malleus bones th<strong>at</strong> wereonce part of reptilian jawstructures evolved in waysth<strong>at</strong> enhanced hearing.MAIN IDEAModern mammals are divided into threemain groups.More than 4500 species of mammal are alive today. They can be classified intothree groups: monotremes, marsupials, and eutherian mammals.MonotremesThe monotremes are mammals th<strong>at</strong> lay eggs. They are remnants of an ancientgroup of mammals th<strong>at</strong> have characteristics of both mammals and reptiles.The group split off from the line th<strong>at</strong> led to the other living mammals sometimeduring the Mesozoic. Their fossils suggest th<strong>at</strong> they once lived throughoutthe Southern Hemisphere. But today only three species of monotremesurvive. The duck-billed pl<strong>at</strong>ypus is found only in Australia and Tasmania.Two types of echidna live in Australia, Tasmania, and New Guinea.VOCABULARYThe name monotreme comesfrom a Greek word th<strong>at</strong> means“single opening,” referring tothe cloaca opening, whichthese mammals have in commonwith birds and reptiles.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 807


FIGURE <strong>26</strong>.18 The shovel-likebill of the duck-billed pl<strong>at</strong>ypus istightly packed with nerve endings.The pl<strong>at</strong>ypus uses this bill toscrape the bottom of rivers andlakes in search of food.FIGURE <strong>26</strong>.19 The red kangarooof Australia gives birth to tinybabies th<strong>at</strong> develop within apouch in the mother’s abdomen.Inside the pouch, the infant<strong>at</strong>taches to a mammary gland,where it will stay until it is m<strong>at</strong>ure.Monotremes such as the pl<strong>at</strong>ypus in FIGURE <strong>26</strong>.18 have a mix of ancestralmammalian and reptilian fe<strong>at</strong>ures. Monotremes have retained reptiliancharacteristics such as• a sprawling posture• a single external opening, called the cloaca, for their urinary, digestive, andreproductive tracts• amniotic eggs with le<strong>at</strong>hery shells th<strong>at</strong> develop outside the bodyMonotremes also have characteristic mammalian fe<strong>at</strong>ures, including mammaryglands. When monotreme babies h<strong>at</strong>ch, their mothers feed them milk.But monotremes do not have nipples. Their babies lick milk from pools ontheir mother’s belly.MarsupialsKangaroos, womb<strong>at</strong>s, koalas, and opossums are a few of the 282 living speciesof marsupial. Marsupials are mammals th<strong>at</strong> give birth to imm<strong>at</strong>ure, underdevelopedlive young th<strong>at</strong> grow to m<strong>at</strong>urity inside a marsupium, or pouch.After fertiliz<strong>at</strong>ion, marsupial embryos begin to develop internally, <strong>at</strong>tached toa placenta th<strong>at</strong> exchanges nutrients and wastes with the mother. But theamount of time the embryo develops inside the mother is very short. Mostmarsupial species give birth only a few weeks after fertiliz<strong>at</strong>ion. The imm<strong>at</strong>urebabies, such as the one seen in FIGURE <strong>26</strong>.19, <strong>at</strong>tach themselves to a nipple insidethe marsupium and nurse for up to six months before emerging from theirmother’s pouch.Fossil evidence shows marsupials once lived all over the world. They havegone extinct over most of their former range. Most living species are foundonly in Australia and New Guinea. A few live in South America.One species, the Virginia opossum, lives in North America.Australian marsupials have diversified into many forms,and there are many examples of convergent evolutionbetween these marsupials and eutherian mammals. Ineach case, the animals share similar ecological roles.For example, Australia is home to mouselike, molelike,ante<strong>at</strong>ing, and gliding marsupials th<strong>at</strong> are physicallysimilar to unrel<strong>at</strong>ed mice, moles, ante<strong>at</strong>ers, andflying squirrels.808 Unit 8: Animals


Eutherian MammalsAll the mammals most familiar to you are eutherians. Eutherian mammalsgive birth to live young th<strong>at</strong> have completed fetal development. Eutherianmammals are commonly called placental mammals, but this term is misleadingbecause most marsupials also use a placenta during embryo development.In most eutherian development, an embryo is <strong>at</strong>tached to themother’s uterine wall. The connection between the fetus and themother forms an organ called the placenta. Through the placenta,the mother delivers oxygen and nutrients to the embryo andremoves waste products. The placenta only forms during gest<strong>at</strong>ionand leaves the mother’s body following birth. The placenta isthe only example of a disposable organ.Eutherian gest<strong>at</strong>ion lasts longer than in marsupials—oftenmonths—and the babies are born <strong>at</strong> a more advanced stage ofdevelopment. In some species, including the Bengal tiger inFIGURE <strong>26</strong>.20, newborns are still rel<strong>at</strong>ively helpless and need extensiveparental care until they can survive on their own. In others,such as deer or horses, the time shortly after birth is when thenewborn is most vulnerable to pred<strong>at</strong>ors, so it is important th<strong>at</strong>they are able to get up and run within hours of birth.After the extinction of the dinosaurs, eutherians quickly filledvacant ecological niches, and the modern groups of mammalsappeared quickly. Rodents and carnivores appeared about 55million years ago, and the first known species of b<strong>at</strong>, elephant,man<strong>at</strong>ee, and horse appeared soon afterwards. Modern eutherians includefast carnivores such as cheetahs, and massive herbivores such as elephants.Three groups of aqu<strong>at</strong>ic eutherians—whales, man<strong>at</strong>ees, and seals—evolvedfrom land-dwelling mammals. B<strong>at</strong>s evolved powered flight. And one groupof prim<strong>at</strong>es, the humans, evolved the ability to think about their ancestors.FIGURE <strong>26</strong>.20 The cubs of thisBengal tiger will stay with theirmother for up to 18 months untilthey are able to hunt on theirown. Many eutherian mammalscare for their young after birth.To find out more about mammals,visit scilinks.org.Keycode: MLB0<strong>26</strong>Compare and Contrast Compare and contrast the advantages and disadvantages ofmarsupial and eutherian mammal reproduction.<strong>26</strong>.4 ASSESSMENTONLINE QUIZClassZone.comREVIEWINGMAIN IDEASCRITICAL THINKINGConnecting CONCEPTS1. Wh<strong>at</strong> fe<strong>at</strong>ures make mammalsdifferent from reptiles?2. How does fetal development differamong the three living groups ofmammals?3. Summarize How did the massextinction th<strong>at</strong> ended the reptilereign help lead to today’s mammaldiversity?4. Classify Monotremes were confusingto early scientists because theyhad both reptilian and mammalianfe<strong>at</strong>ures. How might scientists haveclassified monotremes differently?5. Ecology A sea turtle may layup to 200 eggs in a nest, thenleave and return to the ocean.When the young turtles h<strong>at</strong>chthey must fend for themselves.How do mammals differ in thenumber of offspring producedand in the role of parental careof offspring?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 809


CHAPTER <strong>26</strong>OPTIONS FOR INQUIRYUse these inquiry-based labs and online activities to deepen yourunderstanding of amniotes.INVESTIGATIONThe Parts of an EggBirds, some reptiles, and even a few mammals lay eggs. Inthis lab, you will dissect and identify the parts of an egg.SKILL ObservingPROBLEM Wh<strong>at</strong> are the parts of an egg, and wh<strong>at</strong> aretheir functions?PROCEDUR1. Use colored pencils to illustr<strong>at</strong>e and label thestructures you observe.2. With the various dissecting tools, carefully chip away<strong>at</strong> the eggshell without breaking the delic<strong>at</strong>eMATERIALS• chicken egg• dissecting tray• Egg Drawing• colored pencils• fine scissors• dissecting needle• dissecting forceps• hand lensmembranes bene<strong>at</strong>h the shell or the yolk. Make observ<strong>at</strong>ions with the hand lensand record them.3. In an unfertilized egg, you will find several structures, including the vitellinemembrane, which surrounds the yolk; a white spot on the yolk called the germinaldisk; and two cordlike strands on either side of the yolk, called chalazae.4. In a fertilized egg, you may find an embryo <strong>at</strong>tached to the yolk and twoadditional membranes within the yolk: the amnion and the allantois.Surrounding the yolk is chorion.5. Use the Egg Drawing to identify and illustr<strong>at</strong>e additional structures.6. When you have identified all structures and investig<strong>at</strong>ed both fertilizedand unfertilized eggs, dispose of the eggs and wash your hands.ANALYZE AND CONCLUDE1. Infer Wh<strong>at</strong> do you think would happen to the yolk if the egg wereto become fertilized?2. Infer Wh<strong>at</strong> is the function of the vitelline membrane and the albumen? Explain.810 Unit 8: Animals


INVESTIGATIONMigr<strong>at</strong>ion and RangeEach year, when thedays begin to getshorter and thetemper<strong>at</strong>ure begins todrop, you may noticeflocks of birds flyingacross the sky. Theseasonal movement ofbirds is called migr<strong>at</strong>ion. Birds use a gre<strong>at</strong>deal of energy to migr<strong>at</strong>e.Tiny ruby-thro<strong>at</strong>ed hummingbirds, for example,spend much of the spring and summer in theeastern United St<strong>at</strong>es and Canada. But each year,they make an incredible migr<strong>at</strong>ion, flying southaround the Gulf of Mexico to Central America, andsome go as far south as Panama. Compare this tothe Arctic tern, which travels over 32,000 kilometers(20,000 mi) per year.In this activity, you will research aspects of birdmigr<strong>at</strong>ion.SKILL ResearchingMATERIALS• pencil• North America mapBIOLOGYCLASSZONE.COMANIMATED BIOLOGYBeak Shape and DietThe shape of a bird’s beak allows it to takeadvantage of specific food sources. Examine aset of bird images and use the shape of eachbeak as a clue to identify the food source.WEBQUESTThere are seven species of sea turtles onEarth; all are endangered or thre<strong>at</strong>ened. Inthis WebQuest, you will explore the thre<strong>at</strong>ssea turtles face and the actions people aretaking to save them. Find out if we canreverse the sea turtles’ p<strong>at</strong>hs to extinction.PROBLEM Why do birds migr<strong>at</strong>e?PROCEDUREChoose three of the following questions to researchand help explain bird migr<strong>at</strong>ion.1. Why do birds migr<strong>at</strong>e?2. How do birds know when to start migr<strong>at</strong>ing?3. How do migr<strong>at</strong>ing birds navig<strong>at</strong>e?4. Wh<strong>at</strong> methods do scientists use to monitor birdmigr<strong>at</strong>ion?5. Wh<strong>at</strong> problems do migr<strong>at</strong>ing birds face?6. Wh<strong>at</strong> are the major routes of bird migr<strong>at</strong>ions inNorth America? On the <strong>at</strong>tached map, shade inareas of major flyways over the United St<strong>at</strong>es.DATA ANALYSIS ONLINEInternal body temper<strong>at</strong>ure can provideinform<strong>at</strong>ion about an unknown amniote.Graph and compare body temper<strong>at</strong>ures offour hypothetical animals over a range ofenvironmental temper<strong>at</strong>ures. Use d<strong>at</strong>a in thegraphs to make inferences about the animals.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 811


CHAPTER<strong>26</strong>@ CLASSZONE.COMKEY CONCEPTS Vocabulary Games Concept Maps Anim<strong>at</strong>ed Biology Online Quizamnionembryochorionallantoisyolk sac<strong>26</strong>.1 <strong>Amniotes</strong>Reptiles, birds, andmammals areamniotes. Organismsth<strong>at</strong> develop inside anamniotic sac are calledamniotes. Inside thissac, an embryo is providedwith the necessarynutrients to help it develop and prepare forlife. <strong>Amniotes</strong> pump blood through pulmonaryand systemic circuits and use lungs to exchangeessential gases with the environment and providefor the body. In ectotherms, the external environmentplays an important role in maintainingbody temper<strong>at</strong>ure, while endotherms control theirbody temper<strong>at</strong>ure by regul<strong>at</strong>ing their metabolism.<strong>26</strong>.2 ReptilesReptiles were the first amniotes. Reptiles comein many shapes and sizes, but all have a threechamberedheart and are ectotherms. Oviparousreptiles lay eggs externally, and viviparous reptilesretain eggs internally to full development.Scientists have traced the ancestorsof modern reptiles based on skullan<strong>at</strong>omy and have determined howmodern birds, reptiles, and mammalsare descended from ancient reptiles.Today, turtles, sphenodonts, snakes andlizards, and crocodilians are the majorreptile groups.Synthesize Your NotesConcept Map Use a concept map like the one below tosummarize distinctive amniote characteristics.<strong>26</strong>.3 BirdsBirds have many adapt<strong>at</strong>ions for flight. All birdsshare unique fe<strong>at</strong>ures such as hollow bones, ahighly modified circul<strong>at</strong>ory system, and fe<strong>at</strong>hers.Bird wings have a convex curved shape, called anairfoil, to enable flight. Their strong chest musclesare <strong>at</strong>tached to a large sternum, or keel. Birdshave a very high metabolism and a unique onewaybre<strong>at</strong>hing system th<strong>at</strong> is highly efficient.Birds are directly descended from dinosaurs. Birdscome in many shapes and sizes, and fe<strong>at</strong>uressuch as wings, beak, and feet are highly adaptedto each species’ niche.<strong>26</strong>.4 MammalsEvolutionary adapt<strong>at</strong>ionsallowed mammals to succeeddinosaurs as a dominantterrestrial vertebr<strong>at</strong>e.Mammals evolved whiledinosaurs were walking Earth.After the dinosaurs wentextinct, many new species ofmammals evolved and filledthe vacant niches. Mammalsshare four fe<strong>at</strong>ures—hair,mammary glands, a modifiedmiddle ear, and a jaw th<strong>at</strong>lets them chew food. Mammals are endotherms,and hair plays an important role in keeping theirbody temper<strong>at</strong>ure stable. Mammary glands producenutrient-rich milk, which is the primaryfood source for growing infant mammals. Thereare three major groups of mammals: monotremes,marsupials, and eutherians.Main Idea Web Use a main idea web like the one below tosummarize the fe<strong>at</strong>ures of mammals, birds, and reptiles.<strong>Amniotes</strong>hairincludeincludeMammalsdeveloparedeveloparein an eggendothermsmiddle ear812 Unit 8: Animals


Chapter AssessmentChapter Vocabulary<strong>26</strong>.1 pulmonary circuit, p. 789systemic circuit, p. 789ectotherm, p. 791endotherm, p. 791<strong>26</strong>.2 reptile, p. 793oviparous, p. 793viviparous, p. 793<strong>26</strong>.3 airfoil, p. 799sternum, p. 801air sac, p. 801<strong>26</strong>.4 mammal, p. 805mammary gland, p. 806monotreme, p. 807marsupial, p. 808eutherian, p. 809Reviewing VocabularyVocabulary ConnectionsWrite a sentence or two to clearly explain how thevocabulary terms in this chapter are connected. Forexample, for the terms mammal and mammary gland,you could write, “The mammary gland is one of theunique characteristics of a mammal.”1. endotherm, mammal2. reptile, viviparous3. marsupial, eutherianGreek and L<strong>at</strong>in Word OriginsUse the definitions of the word parts to answer thefollowing questions.Partpulmo-endo--parousMeaninglunginnerto give birth4. Explain why the prefix pulmo- is used to describe bloodcircuits.5. Why is the prefix endo- used to describe thetemper<strong>at</strong>ure regul<strong>at</strong>ion str<strong>at</strong>egy of mammals and birds?6. How is the meaning of the suffix -parous rel<strong>at</strong>ed to itsuse in the word oviparous?Compare and ContrastDescribe one similarity and one difference betweenthe two terms in each of the following pairs.7. pulmonary circuit, systemic circuit8. oviparous, viviparous9. endotherm, ectothermReviewing MAIN IDEAS10. Name the four membranes found in an amniotic egg andexplain the function of each.11. Describe one similarity and one difference between thefunctions of a three-chambered heart and those of afour-chambered heart.12. The desert tortoise, an ectotherm, spends as much as95 percent of its time in underground burrows. Evenin a pred<strong>at</strong>or-free environment, why might it have todo this?13. Birds live in hot deserts and in Antarctica. How is itpossible for birds to live in hot and frigid environmentswhere reptiles cannot survive?14. Wh<strong>at</strong> are two ways th<strong>at</strong> reptiles can reproduce?15. Summarize the rel<strong>at</strong>ionships between modern birds,reptiles, and mammals and their ancient ancestors.16. Compare how snakes and lizards find prey with howcrocodiles find prey.17. Wh<strong>at</strong> five pieces of evidence indic<strong>at</strong>e th<strong>at</strong> birds evolvedfrom theropod dinosaurs?18. Wh<strong>at</strong> is the sternum? How does it help make flightpossible for birds?19. How is the reproductive system of a bird adapted forflight?20. Wh<strong>at</strong> three parts of a bird’s body can indic<strong>at</strong>e wh<strong>at</strong>ecological niche the bird fills?21. How is the mammalian middle ear different from th<strong>at</strong>of reptiles?22. How does development differ among the three groupsof mammals?Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 813


Critical Thinking23. Analyze A person goes out for a jog wearing a jacketbecause the morning is cool. After about 15 minutes, theperson feels very warm and has to take off the jacket,even though the temper<strong>at</strong>ure hasn’t changed. Explainwh<strong>at</strong> is happening.24. Classify Imagine th<strong>at</strong> a new animal has been discoveredin the rain forest. It has four limbs and a tail. Scientistsobserve th<strong>at</strong> it can e<strong>at</strong> prey larger than its head. It givesbirth to live young. Based on this inform<strong>at</strong>ion, howwould you classify this animal? Explain your answer.25. Apply Explain why the number of n<strong>at</strong>ive reptile speciesdecreases as you move away from Earth’s equ<strong>at</strong>or.<strong>26</strong>. Analyze Fe<strong>at</strong>hers are one of the most importantadapt<strong>at</strong>ions for birds. Why are fe<strong>at</strong>hers a more usefuladapt<strong>at</strong>ion for flying than hair?27. Infer Elephants and leopards both live in Africa, where itis hot. But elephants have very little hair, and leopardshave a full co<strong>at</strong> of hair. Explain why this might be.28. Analyze Though it is bad manners, why is it possible fora person to talk while chewing a mouthful of food?Interpreting VisualsUse the following illustr<strong>at</strong>ion to answer the next threequestions.to bodyto lungs3to body1from lungs2Analyzing D<strong>at</strong>aThe table below shows the weight loss of two boxturtles during hibern<strong>at</strong>ion. A box turtle should loseonly about 1 percent of its body weight during eachmonth of hibern<strong>at</strong>ion and no more than 5 percentduring the entire hibern<strong>at</strong>ing period. Use the d<strong>at</strong>a toanswer the next two questions.WEIGHT LOSS DURING HIBERNATIONTurtle Nov Dec Jan Feb MarNo. 1 600g 594g 588g 582g 576gNo. 2 600g 590g 585g 580g 576g32. Graph Which type of graph would best represent bothsets of d<strong>at</strong>a in the table? Why?33. Evalu<strong>at</strong>e Based on the differences in mass over thecourse of hibern<strong>at</strong>ion, which turtle will be healthier <strong>at</strong>the end of hibern<strong>at</strong>ion? Explain your reasoning.Connecting CONCEPTS34. Write a Script Birds, reptiles, and mammals coexist inmany environments on Earth. But many times their p<strong>at</strong>hscross and confront<strong>at</strong>ions occur. Perhaps while a lion isfeeding, a vulture may fly down to try and get a bite toe<strong>at</strong>, or maybe a bird’s nest is being invaded by a reptile.Choose a place where two very different amniotesmight interact, and write a script of their convers<strong>at</strong>ion.Using wh<strong>at</strong> you have learned about birds, reptiles, andmammals and how they function, have them discussadvantages and disadvantages of each other’s lifestylesand how their conflict could be resolved.35. Apply <strong>Look</strong> again <strong>at</strong> the picture of the tarsier onpage 787 and read the description. Despite body partsth<strong>at</strong> might remind you of other types of animals, whyare scientists sure th<strong>at</strong> the tarsier is a mammal?29. Analyze Blood coming from the lungs enters which partof this heart? Give the number and identify the part.30. Analyze Blood going to the body comes from whichpart of the heart? Give the number and identify the part.31. Synthesize Is this a three-chambered heart or a fourchamberedheart? Explain how you know.814 Unit 8: Animals


For more test practice,go to ClassZone.com.1. A researcher studies dairy cows to determineif feed type affects milk production. Theresearcher gives each cow one of the threetypes of feed for a month and measures milkproduction. Which of the following sources oferror were unavoidable in this experiment?A the genetic make up of cows in each groupB the average age of cows in each groupC the number of cows in each groupD the types of cows in each group2.Fossils discovered1000Fossils Discovered <strong>at</strong> Hypothetical Site750500AB250C0500 250 1Millions of years agoThis graph shows the number of fossils found <strong>at</strong>a hypothetical site from each time period overthe past 500 million years. Which of thesest<strong>at</strong>ements is best supported by the d<strong>at</strong>a?A Many speci<strong>at</strong>ion events occurred <strong>at</strong> Node A.B Nodes B and D indic<strong>at</strong>e a lack of biodiversity.C Species diversity increased after Node D.D A possible mass extinction occurred <strong>at</strong> Node C.3. During the summer, the arctic fox producesenzymes th<strong>at</strong> cause its fur to become reddishbrown. These enzymes do not function duringthe winter, causing the fox’s fur to become whiteand blend in with the snow. Which of thefollowing st<strong>at</strong>ements is most likely true?A The genes in arctic fox popul<strong>at</strong>ions areunstable.B Reddish brown fur during the fall is likely notselected for in arctic fox popul<strong>at</strong>ions.C White fur during the winter is a trait th<strong>at</strong> wasselected for in arctic fox popul<strong>at</strong>ions.D The enzyme th<strong>at</strong> controls fur color is notaffected by temper<strong>at</strong>ure.D4. <strong>Amniotes</strong> are multicellular animals whoseembryos develop in an enclosed membrane.Wh<strong>at</strong> else must be true of all amniotes?A They can only reproduce asexually.B Fertiliz<strong>at</strong>ion is always external.C They lay eggs during their life cycle.D Half of their DNA comes from each parent.THINK THROUGH THE QUESTIONFirst, think about wh<strong>at</strong> an embryo is. Can anembryo be produced asexually? Next, elimin<strong>at</strong>eanswer choices th<strong>at</strong> could be true for someamniotes, but may not be true for all amniotes.5. During chewing, digestive enzymes in themouths of mammals begin breaking down foodparticles. Which is true about enzymes?A Without enzymes, certain chemical reactionswould require more energy input.B Once enzymes react, new ones must replacethose th<strong>at</strong> were changed during the reaction.C Enzymes work faster <strong>at</strong> high temper<strong>at</strong>ures.D Enzymes bond to substr<strong>at</strong>es, forming newmolecules.6.These illustr<strong>at</strong>ions show the bones of theforelimbs of three organisms. The similarities inbone arrangement supports the hypothesis th<strong>at</strong>these organismsA are members of one species.B descended from a common ancestor.C have adapt<strong>at</strong>ions for similar environments.D have the same genetic inform<strong>at</strong>ion.Chapter <strong>26</strong>: A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Amniotes</strong> 815

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