Humans have always been fascinated by and sometimes

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1 31 1 Reptiles Humans have always been fascinated by and sometimes frightened of reptiles. Some people fear snakes because of their venomous bites or the way they crawl. Explorers encounters with lizards and crocodiles inspired images of dragons in European folk tales. Turtles, too, are the subject of many a fable. The truth about reptiles is that they are as astonishing as any creatures of human imagination. What Is a Reptile? The basic body plan of a reptile is typical of land vertebrates: a well-developed skull, a backbone and tail, two limb girdles, and four limbs. The iguana in Figure 31 1 exhibits this body plan. Two types of reptiles have slightly different body plans. Snakes are mostly limbless, while turtles have hard shells that are fused to their vertebrae. What characteristics do snakes, turtles, and other reptiles share? A reptile is a vertebrate that has dry, scaly skin, lungs, and terrestrial eggs with several membranes. These characteristics enable reptiles to live their entire lives out of water, unlike their amphibious relatives. Reptilian skin is dry and often covered with thick, protective scales. These scales may be smooth or rough. A reptile s body covering helps prevent the loss of body water in dry environments. But dry, waterproof skin can also be a disadvantage to reptiles. Because the tough, scaly layer of skin does not grow when the rest of a reptile grows, it must be shed periodically as the reptile increases in size. Today, reptiles are widely distributed on Earth. Temperate and tropical areas contain populations of reptiles that are remarkably diverse in appearance and lifestyle. The only places on Earth that most reptiles cannot live in are very cold areas. The reason for this will soon be apparent. for reptiles? Print: What are the advantages of dry, scaly skin Figure 31 1 Like all reptiles, this green iguana has lungs and dry, scaly skin. These characteristics help the iguana live on land. SECTION RESOURCES Laboratory Manual A, Chapter 31 Lab Teaching Resources, Lesson Plan 31 1, Adapted Section Summary 31 1, Adapted Worksheets 31 1, Section Summary 31 1, Worksheets 31 1, Section Review 31 1 Reading and Study Workbook A, Section 31 1 Adapted Reading and Study Workbook B, Section 31 1 Key Concepts What are the characteristics of reptiles? How are reptiles adapted to life on land? What are the four living orders of reptiles? Vocabulary ectotherm amniotic egg carapace plastron Reading Strategy: Outlining Before you read, use the headings in this section to make an outline about reptiles. As you read, add phrases or a sentence about each topic and subtopic in your outline. Issues and Decision Making, Issues and Decisions 34 Technology: itext, Section 31 1 Transparencies Plus, Section 31 1 Section FOCUS Objectives Describe the characteristics of reptiles Summarize the evolution of reptiles Explain how reptiles are adapted to life on land Identify the four living orders of reptiles. Vocabulary Preview Explain that the term ectotherm comes from the Greek words ecto, meaning external, and therm meaning heat. Ask: How do you think ectothermic animals maintain their body temperature? (By interacting with the environment; for example, moving into shade or into sunlight) Reading Strategy Review the structure of an outline. Remind students to include Vocabulary terms and Key Concepts in their outlines. 2 INSTRUCT What Is a Reptile? Comparing and Contrasting Students can make a Venn diagram to compare the characteristics of amphibians and reptiles. Ask: Do reptiles and amphibians have any characteristics in common? (Answers include lungs, backbone, limbs.) In what ways are reptiles better suited to live on land? (Scaly, waterproof skin keeps them from drying out; eggs that hatch on land do not need water.) Encourage students to continue making comparisons between amphibians and reptiles throughout the section. Answer to... The skin protects the body and prevents loss of body water in dry environments. Reptiles and Birds 797

2 31 1 (continued) Evolution of Reptiles Saurian describes an animal that has the characteristics of a lizard. Using Models Students can organize the sequence of events in the evolution of reptiles by making a timeline. Encourage students to customize their timelines to help them organize particular facts or events. For example, English language learners might wish to include phrases in their native languages. Advanced learners might add additional details about the time periods or the evolutionary steps that are not described in the section. Other students might illustrate their timelines with plants and animals living during the time periods. Make Connections Environmental Science Explain to students that climate changes always affect plants and animals. Ask: Why would a change in climate cause some animal populations to decline and others to grow? (Animals that cannot adapt to the changes will die out. Those that are more adaptable more genetically diverse especially when environmental change is rapid, can better survive in the new climate and will increase in number.) Discuss the ways in which people have changed many environments in the world. Ask: How do these changes in the environment affect the plants and animals there? (Some cannot adapt to changes and become endangered or extinct. Others are able to thrive in the changes, sometimes even becoming a nuisance.) You might wish to lead the discussion into a debate about the pros and cons of changing the environment for the benefit of people or for preserving natural habitats for other organisms. Dinosaur is a combination of two Greek words: deinos, meaning terrible, and sauros, meaning lizard. The suffix -ian is used to turn a noun into an adjective. The adjective dinosaurian, for example, describes a dinosaurlike animal. What do you think the adjective saurian describes? Figure 31 2 In the Triassic Period, reptiles such as these lived in the forests. The herbivorous Plateosaurus (left), nibbling on leaves, was a dinosaur, as were the group of carnivorous Coelophysis (center). The large carnivorous Teratosaurus (right) was a reptile but not a dinosaur. Observing What characteristics did these reptiles have in common with modern reptiles? Evolution of Reptiles SUPPORT FOR ENGLISH LANGUAGE LEARNERS Comprehension: Key Concept Beginning On the board, rewrite the boldface sentence (page 800) as individual sentences that each express one adaptive characteristic of reptiles, such as, Strong limbs contributed to the success of reptiles on land. Explain each characteristic. Have students construct a concept circle with Success of reptiles on land in the center and the adaptive characteristics linked to the center by lines. To colonize dry habitats, animals needed a way to reproduce that did not require depositing eggs into water. Reptiles, which evolved from amphibian-like ancestors, were the first vertebrates to develop this adaptation. The fossil of the first known reptile dates back to the Carboniferous Period, some 350 million years ago. As the Carboniferous Period came to a close and the Permian Period began, Earth s climate became cooler and less humid. Many lakes and swamps dried up, reducing the available habitat for waterdependent amphibians. Under these drier conditions, the first great adaptive radiation of reptiles began. These environmental pressures had a negative impact on the survival of many amphibian populations. Mammal-like Reptiles By the end of the Permian Period, about 245 million years ago, a great variety of reptiles roamed Earth. One early group was the mammal-like reptiles, which displayed a mix of reptilian and mammalian characteristics. These chordates eventually came to dominate many land habitats. Toward the end of the Triassic Period, about 215 million years ago, another group of reptiles the dinosaurs became dominant. Enter the Dinosaurs During the late Triassic and Jurassic periods, a great adaptive radiation of reptiles took place. The vast diversity and abundance of reptiles during that time are the main reasons why the Mesozoic Era is often called the Age of Reptiles. Two separate groups of large aquatic reptiles swam in the seas. Ancestors of modern turtles, crocodiles, lizards, and snakes populated many land habitats. And dinosaurs were everywhere. Figure 31 2 shows two dinosaurs, Plateosauras and Coelophysis. The illustration also shows another kind of reptile, Teratosaurus. Intermediate Read aloud the boldface sentence on page 800. Ask individual students, including some ESL students, to identify characteristics that contributed to reptiles success. Then, pair ESL students with English-proficient students. Each pair should work together to summarize the contents following one of the green headings (Body Temperature Control, etc.). 798 Chapter 31

3 A Massive Controversy Dinosaurs were the largest animals ever to walk on Earth. The plant-eating dinosaur Brachiosaurus reached lengths greater than 22 meters and had a mass of about 50,000 kilograms. It would take about 10 elephants to match the mass of one Brachiosaurus. How could the skeleton of such an animal support its immense mass? Imagine that you are a paleontologist searching for an answer to this question. Your job is to examine fossil skeletons of large dinosaurs for clues. Defining the Problem Use your own words to describe the problem you face. Organizing Information List the kinds of skeletal adaptations that would help a dinosaur support its mass. Dinosaurs ranged in size from small to enormous. They ran on two legs or lumbered along on four. Some, like Plateosaurus, ate leafy plants. Coelophysis and other hunters traveled in herds. Others, such as duckbilled Maiasaura, lived in small family groups, caring for their eggs and young in carefully constructed nests. Certain dinosaurs may even have had feathers, which may have evolved as a means of regulating body temperature. All of the dinosaurs, however, belonged to one of two major groups: the Ornithischia (awr-nuh-thish-ee-uh), or bird-hipped dinosaurs, and the Saurischia (saw-rish-ee-uh), or lizard-hipped dinosaurs. From one of these two branches of dinosaurs, probably the Saurischia, came the earliest members of evolutionary lines that would lead to modern birds. Exit the Dinosaurs At the end of the Cretaceous Period, about 65 million years ago, a mass extinction occurred worldwide. This extinction was caused by a dramatic series of natural disasters. These disasters probably included a string of massive volcanic eruptions and lava flows, the dropping of sea level, and a huge asteroid or comet smashing into what is now the Yucatán Peninsula in Mexico. The asteroid or comet collision produced major forest fires and enormous dust clouds. After these events, dinosaurs, along with many other animal and plant groups, became extinct. The disappearance of these organisms during the late Cretaceous Period provided opportunities for other kinds of organisms to evolve on land and in the seas. How did the extinction of the dinosaurs pave the way for modern reptiles? BIOLOGY UPDATE Creating a Solution Carefully study the above illustration of a large dinosaur. Make a model of the part of the spinal column that is supported by the animal s legs. Include the legs in the model. Make another model of an alternative shape for the spinal column, one that is not curved. Presenting Your Plan Describe what you might do to each model to discover which would support a greater mass. Show how you would test the models. Next to the models, place a card describing the steps in your test. NSTA For: Links on dinosaur extinction Visit: Web Code: cbn-9311 Scientists used to think that Brachiosaurus stayed submerged in water to help support its body weight. However, now scientists know that water pressure at the depths required to cover the body would have prevented the lungs from filling with air. Brachiosaurus had a strong, lightweight skeleton with broad, columnar legs that were probably strong enough to support its full weight. Defining the Problem Sample answer: Determine the features of the Brachiosaurus skeleton that enabled it to support its mass. Organizing Information Accept all reasonable responses. These include thick leg bones, legs placed directly under body, quadruped, lightweight vertebral column, large hip bones, and curved backbone. Creating a Solution Display diagrams of various sauropod skeletons for students to observe. You might also display skeletons of smaller dinosaurs for the sake of comparison. Provide students with materials, such as modeling clay or toothpicks and glue, to make their models. They might also draw sketches of the skeletons instead of building a threedimensional model. Presenting Your Plan Most students will describe a test in which they add weight to the top of their skeleton models. Assess the testing plans for logic, clarity, comprehensiveness, and creativity. NSTA Download a worksheet on dinosaur extinction for students to complete, and find additional teacher support from NSTA SciLinks. Evidence for extinction The impact that made the Chicxulub crater in the Yucatán Peninsula is thought by some to have caused the mass extinction at the end of the Cretaceous Period. Recently, a planetary geoscientist, Peter Schultz, analyzed the Chicxulub crater and compared it to craters on the moon, Venus, and Mercury. He concluded that the asteroid hit Earth at an angle pointing toward the northwest. He theorizes that a huge cloud of hot vapor continued northwest, instantly setting fire to most of North America. This scenario helps explain why the extinction rate of plants in North America was at least triple that in the rest of the world. It also explains why land species living in North America were nine times more likely to become extinct than aquatic species. This hypothesis will require further substantiating evidence. Answers to... The extinction provided opportunities for other kinds of organisms to evolve. Figure 31 2 Backbone; lungs; dry, scaly skin; terrestrial eggs Reptiles and Birds 799

4 31 1 (continued) Form and Function in Reptiles Demonstration Demonstrate how ectothermic animals control their body temperature by placing a rock under a heat lamp, a rock in cool water, and a rock in a shady spot. Have students predict the relative temperatures of the tops of the rocks in each location. Then, read the temperature of each location on a thermometer. (The rock under the heat lamp will be warmest.) Discuss different ways in which students keep themselves warm or cool. Then, relate their behaviors to the behaviors of ectotherms in controlling their body temperature. Observing If you have a reptile as a classroom pet, give students the opportunity to observe it feeding. Invite students to point out any special adaptations the reptile has for getting and eating food. For example, snakes have fangs to deliver poison to their prey or to hold the prey while swallowing it. Challenge students to classify the reptile as a carnivore or a herbivore. Have them infer the structure of its digestive system based on its feeding mode. (Herbivores have longer digestive tracts.) Figure 31 3 The gaboon viper, like all snakes, is entirely carnivorous. It eats mice and other small mammals by stretching its jaws wide and swallowing its prey whole. Inferring Besides feeding, what other function might fangs serve in snakes? Form and Function in Reptiles Most reptiles have adapted to a fully terrestrial life. Tough, scaly skin is one adaptation to this type of life. Welldeveloped lungs; a double-loop circulatory system; a water-conserving excretory system; strong limbs; internal fertilization; and shelled, terrestrial eggs are the other adaptations that have contributed to the success of reptiles on land. In addition, reptiles can control their body temperature by moving to a different place. Body Temperature Control The ability to control their body temperature is an enormous asset for active animals. All the animals that you have read about so far are ectotherms (EK-toh-thurmz). Ectotherms rely on behavior to help control body temperature. Turtles, snakes, and other modern reptiles are all ectotherms. To warm up, they bask in the sun during the day or stay under water at night. To cool down, they move to the shade, go for a swim, or take shelter in underground burrows. Feeding Reptiles eat a wide range of foods. Iguanas, which are herbivores, tear plants into shreds and swallow the tough, fibrous chunks. Their long digestive systems enable them to break down plant material. Many other reptiles are carnivores. Snakes, for example, prey on small animals, bird eggs, or even other snakes, grabbing them with their jaws and swallowing them whole as shown in Figure Crocodiles and alligators eat fish and even land animals when they can catch them. Most reptiles eat insects. Chameleons have sticky tongues as long as their bodies that flip out to catch insects. Respiration The lungs of reptiles are spongy, providing more gas-exchange area than those of amphibians. This isn t surprising, because most reptiles cannot exchange gases through their skin the way many moist-skinned amphibians do. Many reptiles have muscles around their ribs that expand the chest cavity to inhale and collapse the cavity to force air out. Several species of crocodiles also have flaps of skin that can separate the mouth from the nasal passages, allowing these crocodiles to breathe through their nostrils while their mouth remains open. To exchange gases with the environment, reptiles have two efficient lungs or, in the case of certain species of snakes, one lung. Circulation Reptiles have an efficient double-loop circulatory system. One of the loops brings blood to and from the lungs, and the other loop brings blood to and from the rest of the body. The diagram in Figure 31 4 shows how blood flows through a turtle s heart. Reptile hearts contain two atria and either one or two ventricles. Most reptiles have a single ventricle with a partial septum, or wall, that helps separate oxygenrich and oxygen-poor blood during the pumping cycle. Crocodiles and alligators, however, have the most developed hearts of living reptiles. The heart consists of two atria and two ventricles an arrangement that is also found in birds and mammals. FACTS AND FIGURES Maintaining body temperature All animals have a specific internal temperature at which their muscles respond best. If body temperature becomes too high, muscles tire easily and other body systems are stressed. Ectothermic animals generally have relatively low metabolic rates when they are resting. Because of this, they do not generate much internal heat and much of this heat is lost because they don t have insulation, like hair or feathers. Controlling body temperature requires heat from the environment. So, for example, a lizard might bask in the sun to warm up. Once its body reaches a certain temperature, it will move around, going about its business. The action of its muscles generates more heat. If the lizard becomes too warm, it will find a shady place to lose heat. 800 Chapter 31

5 Kidney Cloaca Bladder Digestive tract Liver Lung Figure 31 4 The internal organs of most reptiles include a three-chambered heart with two atria and one partially divided ventricle. Interpreting Graphics According to the diagram, how does blood flow through a turtle s heart? Excretion Urine is produced in the kidneys. In some reptiles, urine flows through tubes directly into a cloaca similar to that of amphibians. In others, a urinary bladder stores urine before it is expelled from the cloaca. Reptiles urine contains either ammonia or uric acid. Reptiles that live mainly in water, such as crocodiles and alligators, excrete most of their nitrogenous wastes in the form of ammonia, a toxic compound. Crocodiles and alligators drink a large amount of water, which dilutes the ammonia in the urine and helps carry it away. In contrast, many other reptiles especially those that live entirely on land do not excrete ammonia directly. Instead, they convert ammonia into a compound called uric acid. Uric acid is much less toxic than ammonia, so it does not have to be diluted as much. In these reptiles, excess water is absorbed in the cloaca, reducing urine to crystals of uric acid that form a pasty white solid. By eliminating wastes that contain little water, a reptile can conserve water. Response The basic pattern of a reptile s brain is similar to that of an amphibian, although the cerebrum and cerebellum are considerably larger compared to the rest of the brain. Reptiles that are active during the day tend to have complex eyes and can see color well. Many snakes also have an extremely good sense of smell. In addition to a pair of nostrils, most reptiles have a pair of sensory organs in the roof of the mouth that can detect chemicals when the reptiles flick their tongues. Reptiles have simple ears with an external eardrum and a single bone that conducts sound to the inner ear. Snakes can also pick up vibrations in the ground through bones in their skulls. Some snakes, such as the viper in Figure 31 5, have the extraordinary ability to detect the body heat of their prey. Heart To lungs From body To body Ventricle Right atrium Incomplete division From lungs Left atrium Figure 31 5 The heatsensitive pits above this eyelash viper s mouth enable it to locate prey, even in total darkness. Snakes that have these pits are commonly called pit vipers. Inferring How would these organs give pit vipers an advantage over other reptiles? Use Visuals Figure 31 4 Have students trace the path of blood through the heart. Make sure they understand that the circulatory system has two loops, just as the amphibian circulatory system has. Point out that oxygenated blood from the lungs and deoxygenated blood from the body go through the single ventricle at the same time. Ask: What structure in the ventricle helps separate oxygen-rich and oxygen-poor blood? (Partial internal walls in the ventricle) Which reptiles have two ventricles instead of one? (Crocodiles and alligators) How does a reptile s brain compare to an amphibian s? FACTS AND FIGURES Excreting nitrogenous wastes Excess amino acids cannot be stored or excreted. They are broken down and used as fuel for the body. Ammonia is produced when amino acids are broken down. Cells cannot survive high concentrations of ammonia. To be transported without harming cells, 1 gram of ammonia must be dissolved in 300 to 500 ml of water. In many small aquatic animals, ammonia simply diffuses from their body tissues directly into the water. Terrestrial animals, however, must conserve water. Most reptiles convert ammonia to uric acid. Uric acid is less toxic than ammonia and less soluble. One gram of uric acid needs only 10 ml of water to be transported. In the excretory system, most of the water is returned to the body, and solid crystals of uric acid are removed as a thick paste. Answers to... It is similar, although the cerebrum and cerebellum are proportionally larger. Figure 31 3 Protection from predators Figure 31 4 From body to right atrium to ventricle to lungs to left atrium to ventricle to body Figure 31 5 They can supplement chemical senses with an ability to sense heat from prey and thus locate prey. Reptiles and Birds 801

6 31 1 (continued) Comparing and Contrasting Give students the opportunity to compare and contrast the positions of limbs in amphibians and reptiles. Students will probably have the best success comparing lizards and salamanders. You might provide three-dimensional models of the animals, schematic diagrams, or photographs. Challenge students to develop a method to quantitate the differences by determining the angles of attachment. Figure 31 6 The shovel-snouted lizard (left) is not moving forward; rather, it lifts its feet to limit contact with the hot desert sand. The sidewinding adder propels itself forward by digging its ventral scales against the dunes while pushing its body into long curving waves. Comparing and Contrasting How are the lizard s legs different from those of an amphibian? Inferring Challenge students to make inferences about the relative survival rates of oviparous and ovoviviparous reptilian embryos. Ask: Which embryos are more likely to survive: turtle eggs abandoned in nests or lizard eggs inside the mother s body? (Lizard eggs; better protected from predators) What adaptive advantage does an ovoviviparous reptile have over an oviparous one? (There is a greater chance of eggs hatching, so it can produce fewer eggs. But point out that the final result may be about the same. In both oviparous and ovoviviparous species, enough survive to perpetuate the species. The oviparous species spend energy producing eggs, whereas the ovoviviparous species spend energy protecting their young.) Figure 31 7 After a female box turtle digs a hole in the ground for her nest, she lays her eggs, dropping them one by one and gently lowering them into the hole with her hind feet. When she finishes, she will cover up her nest and leave without a backward glance. Inferring Why would it be an advantage for turtles to lay a large number of eggs? Movement Compared with most amphibians, reptiles with legs tend to have larger, stronger limbs that enable them to walk, run, burrow, swim, or climb. The legs of some reptiles are also rotated further under the body than those of amphibians, enabling reptiles to carry more body weight. The legs and feet of many aquatic turtles have developed into flippers. Figure 31 6 shows some ways that reptiles can move. As with amphibians, the backbones of reptiles help accomplish much of their movement. Reproduction All reptiles reproduce by internal fertilization, in which the male deposits sperm inside the body of the female. Most male reptiles have a penislike organ that allows them to deliver sperm into the female s cloaca. After fertilization has occurred, the female s reproductive system covers the embryos with several membranes and a leathery shell. Most reptiles are oviparous, laying eggs that develop outside the mother s body. Some species, such as the box turtle in Figure 31 7, lay their eggs in carefully prepared nests, then abandon them. Alligators also lay their eggs in nests, but they guard the eggs until they hatch, and provide some care after hatching. Some snakes and lizards are ovoviviparous, and the young are born alive. By carrying her eggs within her body, the female can protect the eggs and keep them warm. Unlike an amphibian egg, which almost always needs to develop in water, the shell and membranes of a reptilian egg create a protected environment in which the embryo can develop without drying out. This type of egg is called an amniotic (am-nee-aht-ik) egg, named after the amnion, one of the four membranes that surrounds the developing embryo. The other three membranes are the yolk sac, the chorion, and the allantois. Find each of these membranes in Figure 31 8 and learn about their functions. The amniotic egg, also seen in birds, is one of the most important adaptations to life on land. What are the four membranes of an amniotic egg? FACTS AND FIGURES Reptilian mothers Surprisingly, alligators and crocodiles are very motherly reptiles. They build a nest with mud, sticks, and vegetation. This compost pile incubates the eggs as the vegetation breaks down. The mother stays near the nest, protecting it from predators. A large percentage of eggs hatch because of this protection. When the mother hears the babies squeaking after hatching, she uncovers the nest and picks up the babies in her mouth. Sometimes she carries the babies to water for food and protection. Baby alligators and crocodiles often stay together in groups, called pods, for their first year. During that year, they are highly susceptible to predators, but their mothers often stay nearby to provide protection. 802 Chapter 31

7 FIGURE 31 8 THE AMNIOTIC EGG Amnion The amnion is a fluid-filled sac that surrounds and cushions the developing embryo. It produces a protected, watery environment. Chorion The chorion regulates the transport of oxygen from the surface of the egg to the embryo and the transport of carbon dioxide, one product of respiration, in the opposite direction. Yolk sac This baglike structure contains a yolk that serves as a nutrient-rich food supply for the embryo. Groups of Reptiles Embryo Shell Since the dinosaurs disappeared, modern reptiles have had plenty of time and space to diversify. The four surviving groups of reptiles are lizards and snakes, crocodilians, turtles and tortoises, and the tuatara (too-uh-tah-ruh). Lizards and Snakes Modern lizards and snakes belong to the order Squamata (skwa-mah-tuh), or scaly reptiles. Most lizards have legs, clawed toes, external ears, and movable eyelids. Some lizards have evolved into highly specialized forms. For example, Gila (HEE-luh) monsters large, stocky lizards that live in the southwestern United States and Mexico have glands in the lower jaw that produce venom for defense against predators. Snakes have lost both pairs of legs during the course of their evolution. Although they are legless, snakes are highly efficient predators, even in the ocean. Some snakes are so small that they resemble earthworms. Others, such as some species of python, can grow to more than 8 meters in length. The ability of certain snakes to produce venom has caused some people to harbor an unjustified fear of all snakes. More people in the United States die from bee stings than from snakebites. In fact, snakes tend to avoid people, not confront them! Allantois The allantois stores the waste produced by the embryo. It later fuses with the chorion and serves as a respiratory organ. An amniotic egg contains several membranes and an external shell. Although it is waterproof, the egg shell is porous, allowing gases to pass through. The shell of reptile eggs is usually soft and leathery. The amniotic egg is one of the most important adaptations to life on dry land. Use Visuals Figure 31 8 Review the structure and function of the amniotic egg. Then, compare the amphibian egg to the reptilian amniotic egg. Ask: How do the parts of the amniotic egg enable it to survive on land? (Shell: protects from drying out; allantois and chorion: gas exchange and waste storage; yolk sac: food for embryo; amnion: water environment to cushion embryo) Why are reptiles completely independent of water for reproduction? (Internal fertilization and amniotic egg) Groups of Reptiles Using Models When students have learned about the four groups of reptiles, challenge them to choose one reptilian order and create a model of their own reptile based on the characteristics of the group. Students can illustrate their models, or they can create models from clay or other materials. Have students present their models to the class. Challenge other students to classify each model into a group based on its characteristics. FACTS AND FIGURES Color, shape, and regeneration Lizards have many adaptations to help them survive. Geckos, for example, have pads on their toes to help them cling to trees and move across diverse terrain speedily to escape predators. Geckos can also cast off their tails if grabbed by a predator. The tailless gecko escapes, and its tail will quickly regenerate. Some lizards blend into the environment to escape predators. Anoles and chameleons change their skin color when frightened or alarmed. The change in skin color can startle a predator or enable the lizard to better blend into its environment. The frilled dragon is a lizard with a frill of skin around its neck. When startled, it extends and opens up the frill, making itself appear larger and more fearsome than it really is. Answers to... Amnion, yolk sac, chorion, and allantois Figure 31 6 The lizard s legs are stronger and larger than those of an amphibian and rotated further under the body. Figure 31 7 To increase the chance that some will survive predation, because turtles do not protect their young from predators Reptiles and Birds 803

8 31 1 (continued) Use Visuals Figure 31 9 Have student volunteers match each reptile pictured to its order. Ask: How do snakes differ from lizards? (Snakes are legless.) Why are tuataras in a separate order from snakes and lizards? (Tuataras lack external ears, have primitive scales, and have a third eye. ) Classifying Display pictures of a snapping turtle, a sea turtle, a tortoise, and a painted turtle. Challenge students to identify which live on land (tortoise) and which live in water (snapping turtle, painted turtle, sea turtle). Make sure students give reasons for their classifications by identifying the adaptations or characteristics that they used for classification. The four orders of living reptiles are the Squamata, Crocodilia, Testudines, and Sphenodonta. The common names of these modern reptile groups are lizards and snakes, crocodilians, turtles and tortoises, and the tuatara. FIGURE 31 9 DIVERSITY OF REPTILES Crocodilians Examples of crocodilians and other reptile groups are shown in Figure Any member of the order Crocodilia including alligators, crocodiles, caimans, and gavials can easily be recognized by its long and typically broad snout and its squat appearance. Crocodilians are fierce carnivores that prey on animals such as fishes, deer, and even humans. Crocodilians are very protective of their young. The females guard their eggs from predators. After the eggs are hatched, the mother gently carries her young to a nursery area and watches over them. Crocodilians live only in the tropics and subtropics, where the climate remains warm year-round. Alligators, and their relatives the caimans, live only in fresh water and are found almost exclusively in North and South America. Crocodiles, on the other hand, may live in either fresh or salt water and are native to Africa, India, and Southeast Asia. Turtles and Tortoises Turtles and tortoises are members of the order Testudines (tes-too-dih-neez). The name turtle usually refers to members of this order that live in water; the name tortoise refers to those that live on land. A terrapin is a turtle that is found in water that is somewhat salty. Nile crocodile Inferring Challenge students to infer why tuataras still exist. Discuss the possible causes of the mass extinction at the end of the Cretaceous Period and the location of New Zealand. Ask: How might an island location contribute to the survival of the tuatara? (Tuataras were isolated from predators and from competition for resources by better adapted animals.) Jackson s chameleon (lizard) Tropical kingsnake Tuatara Red-eared slider turtle BIOLOGY UPDATE Saving sea turtles Sea turtles have inhabited Earth s oceans for millions of years. However, their existence on Earth is threatened. Their demise has been caused by many different factors, but all of them are the result of human activity. Sea turtles are hunted directly for their meat, eggs, leather, and shells. They are harmed indirectly by their accidental capture in fishing nets, by ingestion of trash, by polluted ocean water, and by the loss of nesting sites. Many laws have been enacted to help protect sea turtles. Recently, several nations from North and South America ratified a treaty to protect sea turtles. A multinational treaty is necessary, because sea turtles have large migratory routes. Identifying these migratory routes has been made easier by tagging turtles with satellite global positioning transmitters. 804 Chapter 31

9 Turtles and tortoises have a shell built into the skeleton, although in a few species the shell is not very hard. The shell consists of two parts: a dorsal part, or carapace, and a ventral part, or plastron. The animal s backbone forms the center of the carapace. The head, legs, and tail stick out through holes where the carapace and plastron join. Tortoises and most turtles pull into their shells to protect themselves. Several other adaptations allow turtles and tortoises to live in a wide range of habitats dry, wet, and in-between. Lacking teeth, these reptiles have horny ridges that cover the upper and lower jaws. The jaws are often powerful enough to deliver a damaging bite. All possess strong limbs that lift their body off the ground when walking or, in the case of sea turtles, to drag themselves across a sandy shore to lay eggs. Tuataras The tuatara is the only surviving member of the order Sphenodonta (sfen-uh-dont-uh). It is found only on a few small islands off the coast of New Zealand. Tuataras resemble lizards, but they differ from lizards in many ways. For example, they lack external ears and retain primitive scales. Tuataras also have a legendary third eye, which is part of a complex organ located on top of the brain. This eye can sense the level of sunlight, but its function is unknown. Ecology of Reptiles Many reptiles are in danger because their habitats have been, and are being, destroyed. In addition, humans hunt reptiles for food, to sell as pets, and for their skins, from which bags, boots, and combs are made. Laws now protect some species, such as sea turtles, which were once numerous in both the Atlantic and Pacific oceans. Sea turtle recovery programs, such as the one shown in Figure 31 10, give many young turtles a head start on survival. Although there are many other programs in place that protect reptiles, more conservation efforts are needed worldwide to counteract their dwindling numbers. Figure This wildlife ranger is retrieving green sea turtle eggs on Turtle Island National Park in Borneo. He will bring the eggs to an incubation station, where they can hatch safe from harm. After hatching, the young turtles will be released to the sea. Inferring What might harm sea turtle eggs that are left on a beach to hatch? Ecology of Reptiles Make Connections Environmental Science Make sure students realize how human activity can change the environment to make it unfavorable for species living there. Ask: How might sea turtles be affected if the beaches on which they lay their eggs become popular tourist beaches? (Eggs have a greater chance of being destroyed; fewer sea turtles will hatch and grow to adulthood.) 3 ASSESS Evaluate Understanding Play a quiz game in which you give students the answers and they give you the questions. Focus on adaptations that enable reptiles to live on land and the features of the four reptile groups. Reteach Instruct students to draw a diagram of a typical reptile that shows the main characteristics of reptiles. They should also show how reptiles are adapted to live on land Section Assessment 1. Key Concept List the main characteristics of reptiles. 2. Key Concept List five ways that reptiles are adapted to life on dry land. 3. Key Concept Name the four orders of modern reptiles and give an example of each. 4. How is excretion carried out in reptiles that live on land? 5. How does a lizard control its body temperature? 6. Critical Thinking Predicting What might happen to reptiles if conditions on Earth became permanently warmer and much damper? Interdependence in Nature In Chapter 4, you learned about different biomes, including deserts. In Chapter 30, you learned about the characteristics of amphibians. Use this knowledge to explain why more reptiles than amphibians can tolerate the hot, dry climate of deserts. Students should explain that reptiles are well adapted to live in a hot, dry desert climate because they have many water-conserving adaptations. For example, reptiles can reproduce in the absence of water because of internal fertilization and the amniotic egg. Their efficient excretory system helps to conserve water, as does their scaly skin. Well-developed lungs eliminate the need for gas exchange through moist skin Section Assessment 1. Vertebrate, scaly skin, lungs, amniotic egg 2. Any five: lungs, double-loop circulatory system, strong limbs, efficient excretory system, shelled eggs, internal fertilization 3. Squamata: lizard, snake; Crocodilia: alligator, crocodile, caiman, gavial; Testudines: turtle, tortoise; Sphenodonta: tuatara 4. They convert ammonia to uric acid. 5. By basking in the sun, moving to shade, resting under water, or moving to burrows 6. Some reptiles might colonize areas that are now too cold for them. Others might die out if they cannot successfully compete with damploving competitors, such as amphibians. If your class subscribes to the itext, use it to review the Key Concepts in Section Answer to... Figure Predators, storms, human activities Reptiles and Birds 805