Section 1 Origin and Evolution of Reptiles Chapter 41 Objectives • Summarizethe factors that led to the rise of reptiles as the dominant land vertebrates. • Identifythree factors that contributed to the success of dinosaurs. • Comparetwo hypotheses to explain the extinction of the dinosaurs. • Identifyexamples of the four modern orders of reptiles. • Describethree characteristics of modern reptiles that make them well adapted to life on land.

Section 1 Origin and Evolution of Reptiles Chapter 41 History of Reptiles Pangaea (the supercontinent formed by the joining of all of Earth’s land masses) had a drier interior climate than the coastal regions. Reptiles were well suited to dry climates.

Section 1 Origin and Evolution of Reptiles Chapter 41 History of Reptiles, continued The Mesozoic era is often called the Age of Reptiles. Reptiles flourished due to: • An abundance of food • A dry climate • A mass extinction of other species

Section 1 Origin and Evolution of Reptiles Chapter 41 Continental Drift (Pangaea) Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs Early in the Mesozoic era, Pangaea started to break apart. • The climate of the land masses started to change. • Some species of reptiles could not adapt and became extinct. • Other species flourished.

Section 1 Origin and Evolution of Reptiles Chapter 41 Breakup of Pangaea

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs, continued The evolution of reptiles has been marked by three mass extinction events, shown to the right.

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs,continued Triassic Dinosaurs • The oldest known dinosaur fossils date from the early Triassic period, about 235 million years ago. • These dinosaurs were small and carnivorous.

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs, continued Several factors contributed to the success of dinosaurs: • Legs positioned under the body made them faster and more agile than other reptiles. • Dinosaurs were well adapted to dry conditions. • A mass extinction at the end of the Triassic period reduced competition.

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs, continued Jurassic and Cretaceous Dinosaurs • The Jurassic period is called the golden age of dinosaurs. • Jurassic dinosaurs included the giant sauropods, carnivorous theropods, and large herbivores like triceratops.

Section 1 Origin and Evolution of Reptiles Chapter 41 Evolution of Dinosaurs, continued Dinosaur Diversity • Dinosaurs were not limited to terrestrial habitats. • Some dinosaurs, such as pterosaurs, flew. • Others, such as ichthyosaurs, inhabited the oceans.

Section 1 Origin and Evolution of Reptiles Chapter 41 Extinction of Dinosaurs • Dinosaurs became extinct about 65 million years ago. • Evidence suggests that environmental conditions over many years endangered dinosaur survival. • Either a single asteroid or multiple asteroid impacts might have triggered a mass extinction event that killed the dinosaurs.

Section 1 Origin and Evolution of Reptiles Chapter 41 Mass Extinction Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles There are four modern orders of reptiles: • Chelonia (turtles and tortoises) • Crocodilia (alligators and crocodiles) • Squamata (snakes and lizards) • Rhynchocephalia (tuataras)

Section 1 Origin and Evolution of Reptiles Chapter 41 Phylogenetic Diagram of Reptiles, Birds, and Mammals

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles, continued Three characteristics contribute to the success of reptiles on land: • The amniotic egg • Watertight skin • Efficient respiration and excretion

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles, continued The amniotic egg: • contains a large amount of yolk which nourishes the developing embryo • is usually surrounded by a leathery or hard shell within which the embryo develops • the embryo is surrounded by several membranes which protect the embryo and exchange gases and wastes

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles, continued Parts of the amniotic egg: • amnion - the thin membrane including the fluid in which the embryo floats • yolk sac - encloses the yolk, the fat-rich food supply for the developing embryo • allantois - stores the nitrogenous wastes produced by the embryo • chorion - surrounds all other membranes and helps protect the developing embryo • albumen - fluid containing protein and water needed by the embryo

Section 1 Origin and Evolution of Reptiles Chapter 41 Amniotic Egg Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Reptiles Chapter 41 Parts of an Amniotic Egg Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles, continued Watertight skin • Amphibians are able to exchange gases and water through their skin. As a result, they risk dehydration through evaporation and must live in moist environments. • Reptiles have thick, dry, scaly skin that prevents water loss. As a result, they are able to live in dry environments. • The scaly covering of reptile skin is made of keratin, a tough fibrous protein that makes up scales, hair, and fingernails.

Section 1 Origin and Evolution of Reptiles Chapter 41 Comparing Amphibian and Reptile Skin Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Reptiles Chapter 41 Success of Reptiles, continued Respiration and excretion • Modern reptiles have developed efficient respiratory and excretory systems that help them conserve water. • Respiratory organs (lungs) located inside the body reduce water loss through evaporation. • Nitrogenous wastes secreted in the form of uric acid, which requires little water for dilution, allows reptiles to lose only small amounts of water in their urine.

Section 1 Origin and Evolution of Reptiles Chapter 41 Key Features of Reptiles

Section 1 Origin and Evolution of Reptiles Chapter 41 Characteristics of Reptiles Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Reptiles Chapter 41 Objectives • Identifyadvantages associated with the structure of a reptile’s heart. • Describethe respiratory system of reptiles. • Describefour methods reptiles use to sense their environment. • Explainhow reptiles regulate their body temperature. • Compare oviparity, ovoviviparity, and viviparity as reproductive strategies.

Section 2 Characteristics of Reptiles Chapter 41 Circulatory System The reptile circulatory system consists of two loops: • Pulmonary loop - carries blood from the heart to the lungs and then back to the heart • Systemic loop - carries blood from the heart to the body and then back to the heart

Section 2 Characteristics of Reptiles Chapter 41 Circulatory System, continued • Most reptiles have a three-chambered heart. • The single ventricle is partially divided by a wall of tissue called a septum. • Reptiles can divert blood from the lungs to conserve energy and warm their bodies. • Crocodiles have a four-chambered heart.

Section 2 Characteristics of Reptiles Chapter 41 Turtle Heart Structure

Section 2 Characteristics of Reptiles Chapter 41 Reptile Heart Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Reptiles Chapter 41 Respiratory System • The lungs of reptiles are large, and the lining may be folded into numerous small sacs called alveoli that increase the internal surface area. • Reptiles inflate their lungs by expanding their ribs. This lowers pressure in the chest cavity and draws air in. • When the ribs relax, air is forced out.

Section 2 Characteristics of Reptiles Chapter 41 Alveolus/Alveoli Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Reptiles Chapter 41 Nervous System • A reptile’s brain has a large cerebrum, a well-developed olfactory lobe, and large optic lobes.

Section 2 Characteristics of Reptiles Chapter 41 Nervous System Reptile senses: • Sight - Reptiles have large, well-developed eyes. • Hearing - Sound waves strike the tympanum (eardrum) and are transmitted by the columella to the inner ear. • Vibrations - Snakes lack a tympanum and can sense only low-frequency sounds and ground vibrations. • Smell - Smell is important for most reptiles. Snakes have a special structure called the Jacobson’s organ, located in the roof of the mouth, that also detects odors. • Heat detection - Pit vipers have a heat-sensitive pit below each eye that detects prey.

Section 2 Characteristics of Reptiles Chapter 41 Thermoregulation • The control of body temperature is called thermoregulation. • All living reptiles are ectotherms. Ectotherms warm their bodies by absorbing heat from their environment. • Endotherms generate heat internally to maintain their body temperature.

Section 2 Characteristics of Reptiles Chapter 41 Thermoregulation, continued Advantages and limitations of ectothermy: • Ectotherms have a slow metabolism and require very little energy. They need about one-tenth as much food as an endotherm of the same size. • Ectotherms cannot live in very cold climates. • Ectothermic metabolism cannot provide enough energy for sustained exertion.

Section 2 Characteristics of Reptiles Chapter 41 Changes in Lizard Body Temperature

Section 2 Characteristics of Reptiles Chapter 41 Comparing Endotherms and Ectotherms Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Reptiles Chapter 41 Reproduction and Parental Care There are three patterns of reproduction among reptiles: • Oviparity - Eggs are laid in a tough protective shell. • Ovoviviparity - Eggs have shells but develop within the female’s body. • Viviparity - Eggs have no shells, develop within the female’s body, and are nourished through a structure called the placenta.

Section 2 Characteristics of Reptiles Chapter 41 Reproduction and Parental Care, continued • Many species of reptiles provide no parental care for their young. • Some species of lizards and snakes guard and warm the eggs until they hatch. • Crocodiles and alligators provide the most parental care of any reptile. They build a nest, guard the nest, and carry the hatched young to the water. A mother crocodile may protect her young for a year or more.

Section 2 Characteristics of Reptiles Chapter 41 External Structures of a Timber Rattlesnake

Section 2 Characteristics of Reptiles Chapter 41 Internal Structures of a Timber Rattlesnake

Section 3 Modern Reptiles Chapter 41 Objectives • Comparethe anatomy of turtles with that of other reptiles. • Describethe structure that allows crocodilians to swallow prey under water. • Explainthree antipredator defenses of lizards. • Describetwo ways snakes subdue their prey. • Identifytwo reasons that tuataras are rarely seen.

Section 3 Modern Reptiles Chapter 41 Order Chelonia • Chelonia includes turtles and tortoises. • Turtles generally refers to chelonians that live in water. • Tortoises generally refers to chelonians that live on land. • Turtles and tortoises have a shell made out of bony plates. • The carapace is the top part of the shell. The plastron is the lower part of the shell. • The vertebrae and ribs are fused to the interior surface of the carapace.

Section 3 Modern Reptiles Chapter 41 Order Crocodilia • Crocodilians are large, aquatic or semiaquatic carnivores. • Order includes crocodiles, alligators, caimans, and gavials. • A valve in the oral cavity covers the esophagus and windpipe, allowing crocodilians to capture and swallow prey underwater.

Section 3 Modern Reptiles Chapter 41 Order Squamata Lizards • Most lizards rely on speed, agility, and camouflage to elude predators. • Some lizards can detach their tail to distract predators. This ability is called autotomy.

Section 3 Modern Reptiles Chapter 41 Order Squamata, continued Snakes • Some snakes kill their prey by wrapping their body around the prey and suffocating it. This is called constriction. • Other snakes kill their prey by injecting venom. • Prey must be swallowed whole. A snake’s jaw and skull are joined by a ligament that allows the snake’s head to stretch around its prey.

Section 3 Modern Reptiles Chapter 41 Order Squamata, continued Snakes can inject venom in three different ways: • Snakes may have grooved fangs at the back of the mouth that guide poison into puncture. • Elapid snakes inject poison through two small, fixed fangs in the front of the mouth. • Vipers inject venom through large, hinged fangs in the front of the mouth.

Section 3 Modern Reptiles Chapter 41 Anatomy of a Snake Click below to watch the Visual Concept. Visual Concept

Table of Contents