Copyright Pearson Prentice Hall 31-1 Reptiles Photo Credit: ©Bruce Coleman, Ltd./Natural Selection Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Reptile? What Is a Reptile? 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. Reptilian skin is dry and covered with thick, protective scales. Scales may be rough or smooth and prevent the loss of body water in dry environments. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Reptile? The scaly layer of skin doesn’t grow, so it must be shed periodically as the reptile increases in size. Today, reptiles are widely distributed on Earth. The only places on Earth that most reptiles cannot live in are very cold areas. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles Evolution of Reptiles Reptiles were the first vertebrates that were not dependent on water for reproduction. The first reptile fossil dates back to the Carboniferous Period. Earth’s climate became cooler and less humid. Lakes and swamps dried up, reducing the available habitat for water-dependent amphibians. Then the first great adaptive radiation of reptiles began. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles Mammal-like Reptiles Displayed a mix of reptilian and mammalian characteristics. These chordates eventually came to dominate many land habitats. Toward the end of the Triassic Period, 215 mya, dinosaurs began to become dominant. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles Dinosaurs During the late Triassic and Jurassic periods, a great adaptive radiation of reptiles took place. 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles Dinosaur structure and behavior varied: Ranged in size from small to enormous. Ran on two legs or on four legs. Ate leafy plants or other animals. Some lived in small family groups and some in large herds. Some may have had feathers as a means of regulating body temperature. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles All of dinosaurs belonged to one of two major groups: Ornithischia, or “bird-hipped” dinosaurs Saurischia, or “lizard-hipped” dinosaurs Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles At the end of the Cretaceous, a mass extinction occurred that killed the dinosaurs as well as other plant and animal groups. It was caused by a dramatic series of natural disasters: string of massive volcanic eruptions lava flows dropping of sea level impact of huge asteroid or comet into the Yucatan Peninsula in Mexico Copyright Pearson Prentice Hall

Form and Function in Reptiles Tough, scaly skin and the ability to control body temperature are two adaptations to terrestrial life. Adaptations that have contributed to the success of reptiles on land are: well-developed lungs a double-loop circulatory system a water-conserving excretory system strong limbs internal fertilization shelled, terrestrial eggs Copyright Pearson Prentice Hall

Form and Function in Reptiles Body Temperature Control  Reptiles are ectotherms. Ectotherms are animals that rely on behavior to control body temperature. To warm up, they bask in the sun or stay under water at night. To cool down, they move to the shade or take shelter in underground burrows. Copyright Pearson Prentice Hall

Form and Function in Reptiles Feeding  Reptiles eat a wide range of foods. Iguanas eat plants. Snakes eat small animals, bird eggs, or other snakes. Crocodiles and alligators eat fish and land animals. Most eat insects, such as the chameleon Copyright Pearson Prentice Hall

Form and Function in Reptiles Respiration  Reptile lungs are spongy, allowing for a larger area of gas-exchange. Many reptiles have muscles around the ribs that expand and collapse the chest cavity. Most reptiles have two lungs, but certain species of snakes have just one lung. Copyright Pearson Prentice Hall

Form and Function in Reptiles Circulation  Reptiles have a double-loop circulatory system: One loop brings blood to and from the lungs. One loop brings blood to and from the rest of the body. Copyright Pearson Prentice Hall

Form and Function in Reptiles Reptile hearts have two atria and either one or two ventricles. Most reptiles have one ventricle with a partial septum, or wall, that separates oxygen-rich and oxygen-poor blood. Crocodiles and alligators have two atria and two ventricles. Copyright Pearson Prentice Hall

Form and Function in Reptiles To body Right atrium From lungs To lungs Left atrium From body The internal organs of most reptiles include a three-chambered heart with two atria and one partially divided ventricle. Incomplete division Ventricle Copyright Pearson Prentice Hall

Form and Function in Reptiles Excretion  Urine is produced in the kidneys. In some reptiles, urine flows in tubes directly into a cloaca. In others, a bladder stores urine before it is expelled. Copyright Pearson Prentice Hall

Form and Function in Reptiles Reptiles that live mainly in water excrete most of their nitrogenous wastes as ammonia. Other reptiles that live mainly on land convert ammonia into uric acid. Uric acid is much less toxic than ammonia. In the cloaca, urine is reduced to crystals of uric acid that form a pasty white solid. By eliminating solid wastes, a reptile can conserve water. Copyright Pearson Prentice Hall

Form and Function in Reptiles Response  Reptilian brains are similar to amphibians. Their cerebrum and cerebellum are more developed than other parts of the brain. Reptiles that are active in the day have complex eyes and see color well. Many snakes also have an extremely good sense of smell. Most reptiles have a pair of nostrils and sensory organs in the roof of the mouth that detect chemicals when reptiles flick their tongues. Copyright Pearson Prentice Hall

Form and Function in Reptiles 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 can detect the body heat of their prey. Copyright Pearson Prentice Hall

Form and Function in Reptiles Movement  Reptiles with legs have large strong limbs that enable them to walk, run, burrow, swim, or climb. Some have legs that are rotated further under the body, enabling them to carry more body weight. The legs and feet of many aquatic turtles have developed into flippers. Reptiles’ backbones help accomplish much of their movement. Copyright Pearson Prentice Hall

Form and Function in Reptiles Reproduction  All reptiles reproduce by internal fertilization, in which the male deposits sperm inside the female’s cloaca. Most reptiles are oviparous, laying eggs that develop outside the mother’s body. After fertilization, the female’s reproductive system covers the embryo with several membranes and a leathery shell. Copyright Pearson Prentice Hall

Form and Function in Reptiles The shell and membranes protect the embryo and prevent the egg from drying out. This type of egg, an amniotic egg, is one of the most important adaptations to life on land. An amniotic egg has four membranes—the amnion, the yolk sac, the chorion, and the allantois. Copyright Pearson Prentice Hall

Form and Function in Reptiles The amnion is a fluid-filled sac that surrounds and cushions the developing embryo. Amnion 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. Copyright Pearson Prentice Hall

Form and Function in Reptiles The chorion regulates the transport of oxygen and carbon dioxide between the surface of the egg and the embryo. Chorion 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. Copyright Pearson Prentice Hall

Form and Function in Reptiles The yolk sac contains the yolk that serves as a nutrient-rich food supply for the embryo. 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. Yolk sac Copyright Pearson Prentice Hall

Form and Function in Reptiles The allantois stores the waste produced by the embryo. Allantois 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Groups of Reptiles The four surviving groups of reptiles are: lizards and snakes crocodilians turtles and tortoises tuatara Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Lizards Modern lizards and snakes belong to the order Squamata. Most lizards have four legs and clawed toes, external ears and movable eyelids. Some lizards have evolved into highly specialized forms. For example, Gila monsters, large, stocky lizards of the SW United States, have glands in the lower jaw that produce venom for defense against predators. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Snakes Snakes have no legs. They range in size beginning as small as an earthworm up to an 8 meter long python. They ability of snakes to produce venom has caused some people to harbor unjustified fear of all snakes. More people die from bee stings than snake bites. Snakes have immovable eyelids and no external ear openings. Snakes are very efficient predators. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Crocodilians Order Crocodilia: alligators, crocodiles, caimans and gavials Crocodilians have long, broad snouts and a squat appearance. They are fierce carnivores and prey on animals such as fishes, deer, and even humans. Females guard their eggs from predators and watch over their young after the eggs hatch. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolution of Reptiles Crocodilians live only where it is warm year-round. Alligators and caimans live only in fresh water and are found almost exclusively in North and South America. Crocodiles live in either fresh or salt water and are native to Africa, India, and Southeast Asia. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Turtles and Tortoises Order Testudines Turtles live in water, tortoises live on land. A terrapin is a turtle that lives in water that is somewhat salty. Turtles and tortoises have a two-part shell built into the skeleton: a dorsal part, or carapace and a ventral part, or plastron. The backbone forms the center of the carapace. The head, legs, and tail emerge from holes where the carapace and plastron join. Copyright Pearson Prentice Hall

Form and Function in Reptiles Liver Heart Kidney Cloaca The internal organs of most reptiles include a three-chambered heart with two atria and one partially divided ventricle. Digestive tract Lung Bladder Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Tortoises and most turtles pull into their shells for protection. Lacking teeth, these reptiles have horny ridges that cover the upper and lower jaws. The jaws are often very powerful. All possess strong limbs that lift their body off the ground when walking or to propel the body when swimming. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Reptiles Tuataras Order Sphenodonta Tuataras are the only surviving members of the order and are found only on a few islands off New Zealand. They resemble lizards in many ways but they lack external ears and retain primitive scales. They have a “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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ecology of Reptiles Ecology of Reptiles Many reptiles are in danger because of habitat destruction. Humans hunt reptiles for food, for pets, and for their skins. Laws protect some species, but more conservation efforts are needed to counteract their dwindling numbers. Copyright Pearson Prentice Hall