Chapter 32: Reptiles and Birds Section 1: Reptiles What Is A Reptile? Reptiles are vertebrate animals that have lungs, a scaly skin, and a special type of egg adaptations that enable them to live their entire life out of water Reptiles are widely distributed over much of the Earth The reptiles thick skin helps prevent loss of body water The tough, scaly layer of skin does not grow when the rest of the reptile grows, so it must be shed periodically when a reptile increases in size What Is A Reptile? Reptilian eggs are surrounded by a shell and several membranes that create a protected environment in which the embryo can develop Amniotic egg Amniotic eggs also contain a yolk The yolk is rich in nutrients that the developing embryo uses until it is ready to hatch What Is A Reptile? Reptiles have an efficient respiratory system To exchange gases with the environment, reptiles have at least one efficient lung The chameleon, a modern reptile, moves slowly and deliberately, creeping up to its insect prey. Its eyes are able to move independently of each other, so that one eye can guide its movements and the other can sight the victim. Unlike most amphibians, reptiles are able to survive quite well in dry environments, as this snake in a cactus shows. Their survival is due in part to their dry, scaly skin, which must be shed periodically. The reptile egg shows adaptations to survive the dryness of life on land. This tiny turtle has just hatched and is breaking free of its shell. Evolution of Reptiles Because several fossils show characteristics of both amphibians and reptiles, it is difficult to say exactly when the first true reptiles appeared on Earth One determining factor that separates living reptiles from amphibians is the type of eggs they produce Because we cannot tell what kind of eggs these fossil animals laid, they must remain on the amphibian-reptilian borderline These animals are often called transition fossils Evolution of Reptiles Throughout most of the Carboniferous Period, amphibians greatly outnumbered reptiles But during the Permian Period, the Earths surface and climate changed dramatically The climate became cooler and less humid Many of the great swamps dried up These changes made life difficult for a large number of water-dependent amphibians But such was not the case with the reptiles It was during this time that they began their great period of adaptive radiation Evolution of Reptiles One early reptile line developed into a fascinating group pf mammal like reptiles that displayed a mix of reptilian and mammalian characteristics Although these animals were extremely successful at first, they became extinct in just a few million years Toward the end of the Triassic Period, about 195 million years ago, the mammal like reptiles were suddenly replaced in the fossil record by another group of reptiles that had remained in the background for millions of years the dinosaurs Evolution of Reptiles During the late Triassic and Jurassic Periods, a great adaptive radiation of the dinosaurs, or terrible lizards, took place The Triassic Period also saw the appearance of crocodiles and alligators, as well as the first birds At the end of the Cretaceous Period, about 65 million years ago, something happened to cause a worldwide mass extinction Evolution of Reptiles Within a few million years, dinosaurs and most other animal and plant groups became extinct Whatever happened at the end of the Cretaceous Period resulted in the death of virtually all the great and terrible lizards The disappearance of the dinosaurs left open many niches for animals, both on land and in the sea Form and Function in Reptiles Reptiles exhibit numerous variations in structure and behavior Some for example, turtle, crocodiles, and lizards move about on four legs Others move about without legs Snakes and certain lizards Feeding Some are herbivores and others are carnivores Some have sharp teeth to capture prey Others kill their prey by drowning it first Some reptiles have sticky tongues that can catch insects All snakes are carnivores. Many snakes eat small mammals. Because they are able to stretch their jaws wide, snakes swallow their prey whole. A chameleon obtains its food by flicking out its sticky tongue over a great distance. Any insects within striking range are gobbled up. Respiration May reptiles are able to expand their chest cavity to inhale and collapse the cavity to force air out Although most reptiles have two lungs, some species of snakes have only one You know that it is impossible for a person to breathe and swallow simultaneously Snakes have a special tube in the floor of their mouth through which they breathe, so they dont suffocate in the time it takes them to swallow their prey This tube can be extended out of a snakes mouth while it is dining Internal Transport Reptiles have a well-developed double-loop circulatory system One of the two loops brings blood to and from the lungs and the other loop brings blood to and from the rest of the body Have a well-developed heart Have a well-developed circulatory system This illustration shows the internal organs of a turtle. The turtles top shell is actually fused to its vertebrae. Other reptiles differ slightly from this body plan. Excretion Eliminate wastes in the form of urine, which is produced in the kidneys Urine flows through tubes directly into a cloaca similar to that of amphibians In some reptiles, a urinary bladder stores urine before it is expelled Response Most reptilian sense organs are well-developed Have complex eyes that contain photoreceptor cells Many snakes have a good sense of smell Some reptiles have simple ears to hear (eardrum, tympanic membrane) Some reptiles are able to gather heat information from their environment Unlike certain snakes, the gila monster does not have fangs to inject its venom. Instead, it bites its prey and lets its venom flow into the open wound. The fangs of this rattlesnake are so long they must fold in order for the snake to close its mouth. Note the position of the animals venom glands. Movement The reptilian muscle and skeletal systems exhibit many advances over those of amphibians Reptiles with legs have larger, stronger limbs whose movements are well-controlled Snakes, which lost their legs in the course of evolution, move by pressing large ventral scales against the ground The sidewinder, a type of rattlesnake, is able to move along shifting desert sands quite quickly. Tiny flaps of skin on its toes enable this gecko to cling to surfaces as smooth as glass. Reproduction Reptiles lay eggs that hatch into animals that resemble small adults Virtually all reptiles reproduce through internal fertilization, which means that a male deposits sperm into the body of the female From the outside, it is extremely difficult to tell the sex of a reptile Most reptiles provide minimal care for their young Tuataras The tuatara is the only surviving member of the order Rhynchocephalia Resembles reptiles that lived during the dinosaur age Tuataras are found only on a few small islands off the coast of New Zealand They are active at night They have a pineal gland that contains cells that are sensitive to light They use it to detect changes in day length Lizards and Snakes Order Squamata Most lizards have legs, clawed toes, external ears, and moveable eyelids Some have evolved into highly specialized forms The monitors are the only reptiles alive today that provide some idea of what small dinosaurs may have been like Quite intelligent and active Eat birds and mammals Largest are the Komodo dragons This male anole is displaying the bright red patch below its chin. The Komodo dragon is one of the largest lizards in the world, reaching a length of about 3 meters. The frilled dragon gets its name from a frill of skin around its neck that can extend, thus making itself appear larger and more fearsome to other animals. Lizards and Snakes Snakes are lizards that have lost both pairs of legs during their evolution Although being legless may seem to be a disadvantage, snakes are efficient and effective predators in the niches they occupy The distribution of snakes on Earth is limited only by temperature Snakes vary in size The ability of certain types of snakes to produce lethal poisons has caused people to fear snakes More people in the US die from bee stings than snake bites Crocodilians Order Crocodilia Alligators, crocodiles, caimans, and gavials Crocodilians are among the largest living reptiles Can grow up to 7m in length Live only in the tropics and subtropics, where the climate is warm year round Alligators and caimans live only in freshwater and are found in the Western Hemisphere Crocodiles may live in either fresh or salt water and are native to Africa, India, and Southeast Asia Turtles Order Chelonia Turtles live in water Tortoises live on land All have some sort of shell covering their body The shell consists of two parts: a dorsal part, or carapace, and a ventral part, or plastron The animals backbone is fused to the inside of the carapace, and its head, legs, and tail stick out through holes where carapace and plastron join Turtles Tortoises usually have a high, domed carapace and stubby, elephant-like legs Tortoises pull into their shells to protect their more delicate body parts In some species,the front end of the plastron is hinged and folds up to further seal out predators Turtles Turtles are adapted to freshwater ponds and lakes or the open sea The legs and feet of many aquatic turtles have developed into flippers Certain aquatic species cannot pull back into their shell completely, but they do have powerful jaws that are capable of biting if attacked How Reptiles Fit into the World Reptiles are important predators in many ecosystems Sea turtles are now in danger of extinction Turtle soup and turtle eggs Used to manufacture jewelry Destruction of nesting sites Chapter 32: Reptiles and Birds Section 2: The Evolution of Temperature Control Control of body temperature is important for animals, particularly in habitats where temperature varies widely with time of day and with season Each animal species has its own preferred operating range of temperatures In terms of how they generate and control their body heat, animals can be classified into two basic groups: ectotherms and endotherms The Evolution of Temperature Control Turtles, snakes, and other modern reptiles are ectotherms, which literally means heat from outside These animals have low metabolic rates when they are resting They do not generate much heat inside their bodies Any heat they do generate is lost to their surroundings These animals must pick up heat from the environment The Evolution of Temperature Control Birds and mammals are endotherms, which literally means heat from inside Birds and mammals have relatively high metabolic rates that generate a significant amount of heat, even when they are resting Body fat and either hair or feathers insulate the body, helping to retain that heat so that it is not lost to the environment Endotherms can move around at night more easily than ectotherms can The Evolution of Temperature Control In nature, lizards and snakes warm up when they need to by basking in the sun When their body reaches the right temperature, they go about their business If they get too hot during the day, reptiles duck into a cool burrow or under a rock to lose heat Neither endothermy nor ectothermy is superior Each strategy has its advantages and disadvantages The Evolution of Temperature Control Ectotherms cannot remain active for long periods Endotherms remain active for a long time In climates that remain warm all the time, ectothermy is a way of conserving energy Endotherms burn lots of calories to generate body heat Chapter 32: Reptiles and Birds Section 3: Birds Birds About 8700 living species belonging to more than 160 families There were even more kinds of birds in the past Paleontologists estimate that more than 100,000 species of birds have become extinct since the Jurassic period What Is a Bird? Birds are endothermic reptile-like animals with an outer covering of feathers, two legs used for walking or perching, and front limbs modified into wings that usually do not have useful claws The single most important feature that distinguishes birds from reptiles is feathers Feathers help birds fly and also keep them warm Birds have several different kinds of feathers What Is a Bird? Contour feathers are large feathers that cover a birds body and wings Used for flight Contain barbs and barbules Preening Down feathers grow underneath and between the contour feathers Short, soft, and fluffy Trap warm air close to a birds body Powder feathers are important to birds that live on or in water Repels water Baby owls are covered with a coat of down feathers. The air spaces in these fluffy feathers help insulate the birds from temperature changes. Most of the down feathers will later be shed and a new coat of contour feathers will grow in. Evolution of Birds The first fossil ever found of an early birdlike animal is called Archaeopteryx and dates from late in the Jurassic Period Its skeleton looks much like a small running dinosaur Had teeth in its beak Had toes and claws on its wings There is much controversy over which fossils are those of birds and when birds first appeared on Earth Archaeopteryx, which lived about 147 million years ago, is the oldest fossil that has been confirmed to be that of a bird. Form and Function in Birds Many characteristic features of birds differ dramatically among species adapted to different ways of life Feathers, wings, bones, beaks, and legs It is important to study birds that live in different habitats and examine the adaptations they show The huge talons of this soaring eagle help the bird catch fish. Woodpeckers hear insects chewing beneath the bark of a tree. The beak of the woodpecker is strong enough to pierce the bark, revealing the bug beneath it. The featherless head of this vulture gives the bird a sinister look, but a lack of head feathers serves a useful function: A featherless head is easy to keep clean. Because vultures often put their head into the carcass of dead animals, cleanliness is important. Feeding Birds have high metabolic rates and burn many calories just to keep warm For that reason, birds need to eat large amounts of food The digestive system of birds shows specializations for carnivorous and herbivorous diets Feeding Many birds have organs called crop and gizzard The crop is an enlarged area of the esophagus, where food can be stored and moistened before it enters the stomach The gizzard is a muscular part of the stomach that often contains small bits of gravel swallowed by a bird Grinds the gravel and food together Crushes food particles and makes them easier to digest Respiration Extremely efficient in taking in oxygen and eliminating carbon dioxide Bird lungs are connected at both the anterior and posterior to large air sacs in the body cavity and bones When a bird inhales, air travels through passageways that lead into the lungs Respiration Some stays in the lungs, however, most goes into the posterior air sacs When a bird exhales, air from the posterior air sacs passes into the lungs for gas exchange Birds are able to remove oxygen from air when they inhale as well as when they exhale Internal Transport Four-chambered heart and two separate circulatory loops One half of the heart receives oxygen-poor blood from the body and pumps this blood to the lungs Oxygen-rich blood returns to the other side of the heart to be pumped throughout the rest of the body This system ensures that oxygen collected by the lungs is distributed with maximum efficiency A birds heart beats quickly From 150 to more than 1000 beats per minute Excretion Eliminate nitrogenous waste by filtering them from the blood in the kidneys Urine flows to the cloaca through the ureters Most water is reabsorbed in the cloaca, leaving uric acid crystals in a white paste like form bird droppings Bird species that are surrounded by sea water have special salt glands near their eyes Work like an extra pair of kidneys, except they specialize in secreting salt Response Birds are quite intelligent Cerebrum controls behaviors such as flying, nest building, care of young, courtship, and mating Cerebellum and medulla are much like those of reptiles Extraordinary well-developed eyes because of large optic lobes in the brain Response The senses of taste and smell are not well developed Small olfactory lobes Lack external ears Some use a magnetic sense to navigate Operates like a built-in compass, responding to Earths magnetic field The huge forward-facing eyes of an owl help this great bird hunt at night. Its eyes are able to spot a tiny mouse foraging among the leaves on the dark floor of a forest. Movement Travel through different environments with wings, bodies, legs, and feet adapted for various types of locomotion Many variations in bird wings, depending on whether the animals soar like eagles, flap their wings steadily like robins, or hover in place like hummingbirds Movement Bones are hollow so that the weight carried in fight is less Large chest muscles that attach directly to the sternum Many birds use their flying ability to migrate between summer breeding grounds in the North and winter resting grounds in the South or the tropics A number of birds have lost their ability to fly Ostriches and penguins Reproduction Similar to that of reptiles Reproductive tracts open to the cloaca Male birds have no external reproductive organs Instead, mating birds press the lips of their cloacas close together to transfer sperm from male to female Most birds incubate their eggs until they hatch The time between laying and hatching varies among species from 13 days to more than 50 days Reproduction When a chick is ready to hatch, it uses a small egg tooth on its bill to make a hole in the shell Some birds are able to take care of themselves as soon as they hatch Other newly hatched birds are blind and totally helpless when they hatch Birds have fascinating courtship and mating behaviors Some species mate for life Other pair up only briefly to mate How Birds Fit into the World Serve as pollinators for a number of plants Eat extraordinary numbers of insects Down feathers are good insulators Favorite foods around the world Raising them is part of the economy in many countries How Birds Fit into the World Healthful source of protein Because domestic strains of chickens and turkeys do not fly, their chest muscles are seldom used, making this part of the bird the juicy and tender white meat The leg and thigh muscles of these birds, used constantly for walking and running, are the dark meat