Reptiles and Birds

Reptiles

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.

What is a reptile? Reptilian skin is dry and covered with thick, protective scales.  This prevents the loss of body water in dry environments. The scaly layer of skin doesn’t grow, so it must be shed periodically as the reptile increases in size.

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.

Evolution of Reptiles Dinosaurs During the late Triassic and Jurassic periods, a great adaptive radiation of reptiles took place. adaptive radiation – a single species or a small group of species has evolved into diverse forms that live in different ways  The Mesozoic Era is often called the Age of Reptiles.

Triassic Reptiles

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.  Some may have had feathers.

Evolution of Reptiles All of dinosaurs belonged to one of two major groups:  Ornithischia, or “bird-hipped” dinosaurs  Saurischia, or “lizard-hipped” dinosaurs At the end of the Cretaceous, a mass extinction occurred that killed the dinosaurs as well as other plant and animal groups.

Form and Function: Reptiles Tough, scaly skin and the ability to control body temperature are two adaptations to terrestrial life.

Form and Function: Reptiles 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

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.

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.  Chameleons eat insects.

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.

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.

Circulation Kidney Liver Heart Cloaca Bladder Lung Digestive tract

Circulation Reptile hearts have two atria and either one or two ventricles.  Most reptiles have one ventricle with a partial septum that separates oxygen-rich and oxygen-poor blood.  Crocodiles and alligators have two atria and two ventricles.

Circulation Right atrium Left atrium Incomplete division Ventricle From body To lungs To body From lungs

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.

Excretion Other reptiles convert ammonia into uric acid.  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.

Response Reptilian brains are similar to amphibians. Their cerebrum and cerebellum are more developed than other parts of the brain.

Response 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 sensory organs in the mouth that detect chemicals when reptiles flick their tongues.

Response 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.

Movement Reptiles with legs have large strong limbs.  Some have legs that are rotated further under the body, enabling them to carry more body weight.

Movement The legs and feet of many aquatic turtles have developed into flippers.  Reptiles’ backbones help accomplish much of their movement.

Reproduction Most reptiles are oviparous, laying eggs that develop outside the mother’s body. All reptiles reproduce by internal fertilization, in which the male deposits sperm inside the female’s cloaca.

Reproduction After fertilization, the female’s reproductive system covers the embryo with several membranes and a leathery shell.  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.

The Amniotic Egg Amnion Chorion Yolk sac Allantois

The Amniotic Egg The amnion is a fluid-filled sac that surrounds and cushions the developing embryo. The chorion regulates the transport of oxygen and carbon dioxide between the surface of the egg and the embryo.

The Amniotic Egg The yolk sac contains the yolk that serves as a nutrient-rich food supply for the embryo. The allantois stores the waste produced by the embryo.

Groups of Reptiles The four surviving groups of reptiles are:  lizards and snakes  crocodilians  turtles and tortoises  tuatara

Lizards

Lizards and Snakes Most lizards have four legs and clawed toes.lizards Most lizards have external ears and movable eyelids. Some lizards have evolved into highly specialized forms.

Snakes

Lizards and Snakes Snakes have no legs. Snakes have immovable eyelids and no external ear openings. Snakes are efficient predators.

Crocodilians

Crocodilians have long, broad snouts and a squat appearance. They 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.

Crocodilians 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.

Turtles and Tortoises Turtles live in water. Tortoises live on land. A terrapin is a turtle that lives in water that is somewhat salty.

Turtles and Tortoises

Turtles and tortoises have a two-part shell built into the skeleton: a dorsal part, or carapace a ventral part, or plastron The head, legs, and tail emerge from holes where the carapace and plastron join. Tortoises and most turtles pull into their shells for protection.

Tuataras Tuataras are found only on a few islands off New Zealand.  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.

Tuataras

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.