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 Earth’s 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 don’t suffocate in the time it takes them to swallow their prey • This tube can be extended out of a snake’s 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 turtle’s 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 animal’s 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
Tiny flaps of skin on its toes enable this gecko to cling to surfaces as smooth as glass. The sidewinder, a type of rattlesnake, is able to move along shifting desert sands quite quickly.
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 animal’s 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
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 bird’s 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 bird’s 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