Section 1 Origin and Evolution of Amphibians Chapter 40 Objectives • Describethe three preadaptations involved in the transition from aquatic to terrestrial life. • Describetwo similarities between amphibians and lobe-finned fishes. • Listfive characteristics of living amphibians. • Namethe three orders of living amphibians, and give an example of each.

Section 1 Origin and Evolution of Amphibians Chapter 40 Adaptation to Land • Preadaptations - are adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection. Lobe-finned fishes had several preadaptations that allowed them to transition to life on land. • bone structure • pouches in digestive tracts for gas exchange • nostrils • higher metabolism • efficient hearts

Section 1 Origin and Evolution of Amphibians Chapter 40 From Fin to Limb

Section 1 Origin and Evolution of Amphibians Chapter 40 Adaptation to Land, continued Characteristics of Early Amphibians Amphibians and lobe-finned fishes share many anatomical similarities, including: • similar skull • similar vertebral column • similar bone structure in fins and limbs • early amphibians had a large tail fin and lateral line canals

Section 1 Origin and Evolution of Amphibians Chapter 40 Characteristics of Early Amphibians

Section 1 Origin and Evolution of Amphibians Chapter 40 Adaptation to Land, continued Diversification of Amphibians • About 300 million years ago amphibians split into two main evolutionary lines. • One line included ancestors of reptiles, the other line included the ancestors of modern amphibians.

Section 1 Origin and Evolution of Amphibians Chapter 40 Adaptation to Land, continued Diversification of Amphibians Today there are about 4,500 species of amphibians belonging to three orders: • Anura - includes frogs and toads • Caudata - includes salamanders and newts • Gymnophiona - includes caecilians (legless tropical amphibians)

Section 1 Origin and Evolution of Amphibians Chapter 40 Modern Amphibians Modern amphibians share several key characteristics • Most change from an aquatic larval stage to a terrestrial adult form, in a transformation called metamorphosis. • Most have moist, thin skin with no scales. • Feet, if present, lack claws and often are webbed. • Most use gills, lungs, and skin in respiration. • Eggs lack multicellular membranes or shells, are usually laid in water, and are usually fertilized externally.

Section 1 Origin and Evolution of Amphibians Chapter 40 Characteristics of Amphibians Click below to watch the Visual Concept. Visual Concept

Section 1 Origin and Evolution of Amphibians Chapter 40 Modern Amphibians, continued Order Anura • Order includes frogs and toads. • Members may be fully aquatic, fully terrestrial, or amphibious. • Most reproduce in water, laying eggs that hatch into swimming larvae called tadpoles. • Larvae are herbivores. Adults are carnivorous and will eat any animal they can capture.

Section 1 Origin and Evolution of Amphibians Chapter 40 Modern Amphibians, continued Order Caudata • Includes salamanders (may also be called newts). • Members may be fully aquatic, fully terrestrial, or amphibious. • Many reproduce in water. Some reproduce on land, with no swimming larval stage. • Larvae and adults are carnivorous. • Some have no lungs, and respire through their skin only.

Section 1 Origin and Evolution of Amphibians Chapter 40 Modern Amphibians, continued Order Gymnophiona • Includes caecilians (legless amphibians that resemble small snakes). • Most are burrowing. They have small eyes beneath skin or bone, and are often blind. • All are carnivorous. • All are thought to have internal fertilization. • Some lay eggs which the female guards, others develop inside the female.

Section 1 Origin and Evolution of Amphibians Chapter 40 Phylogenetic Diagram of Amphibians

Section 1 Origin and Evolution of Amphibians Chapter 40 Types of Amphibians Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Amphibians Chapter 40 Objectives • Relatethe structure of amphibian skin to the types of habitats in which amphibians can survive. • Identifythree adaptations for life on land shown by the skeleton of a frog. • Sequencethe flow of blood through an amphibian’s heart. • Describehow a frog fills its lungs with air. • Describethe digestive and excretory systems of amphibians. • Discussan amphibian’s nervous system.

Section 2 Characteristics of Amphibians Chapter 40 Skin Amphibian skin serves two important functions: • Respiration - The skin is permeable to gases and water. Mucous glands secrete a lubricant that keeps the skin moist in air. • Protection - The skin protects amphibians from infection and secretes a foul-tasting or poisonous mucus that protects amphibians from predators.

Section 2 Characteristics of Amphibians Chapter 40 External Structure of a Frog

Section 2 Characteristics of Amphibians Chapter 40 Skeleton A strong skeleton supports the body of amphibians against the force of gravity. • Vertebrae interlock to form a strong, rigid structure. • Strong limbs assist with standing and walking. • Pectoral and pelvic girdles transfer weight to the limbs. • Skeletons of frogs are specialized for jumping and landing.

Section 2 Characteristics of Amphibians Chapter 40 Skeleton, continued • Fused bones add strength to the forelimbs and hind limbs. • Thick arm bones and pectoral girdle absorb shock of landing. • Long hind legs allow frogs to jump farther. • Lengthened pelvic girdle and fused vertebrae add support.

Section 2 Characteristics of Amphibians Chapter 40 Circulatory System The circulatory system is divided into two loops. • Pulmonary circulation - carries deoxygenated blood from the heart to the lungs and back to the heart. • Systemic circulation - carries oxygenated blood from the heart to the body and back to the heart.

Section 2 Characteristics of Amphibians Chapter 40 Circulatory System, continued Three chambered heart:

Section 2 Characteristics of Amphibians Chapter 40 Amphibian Heart Structure

Section 2 Characteristics of Amphibians Chapter 40 Frog Heart and Double-Loop Circulation Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Amphibians Chapter 40 Respiration Amphibians use two forms of respiration • Pulmonary respiration - respiration through the lungs • Cutaneous respiration - respiration through the skin

Section 2 Characteristics of Amphibians Chapter 40 Respiration, continued Amphibians use positive pressure breathing, shown below.

Section 2 Characteristics of Amphibians Chapter 40 Amphibian Lung Structure

Section 2 Characteristics of Amphibians Chapter 40 Respiration in Amphibians Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Amphibians Chapter 40 Digestive System • Includes the pharynx, esophagus, stomach, liver, gallbladder, small intestine, large intestine, and cloaca. • The upper part of the small intestine is called the duodenum. • The coiled middle portion of the small intestine is the ileum. • A membrane that holds the small intestine in place is called the mesentery. • Waste materials are stored in the cloaca and exit the body through the vent.

Section 2 Characteristics of Amphibians Chapter 40 Digestive System, continued Accessory Glands • The liver produces bile, which is stored in the gallbladder and helps break down fat. • The pancreas secretes enzymes that help break down food into particles that can be absorbed by the blood.

Section 2 Characteristics of Amphibians Chapter 40 Internal Structure of a Frog

Section 2 Characteristics of Amphibians Chapter 40 Excretory System • The kidneys are the primary excretory organ, and filter nitrogenous wastes from the blood. • Wastes combined with water are known as urine. • Urine flows from the kidneys to the cloaca and then to the urinary bladder, which branches off the cloaca. • Nitrogenous wastes are converted from ammonia to urea, which is highly concentrated and helps conserve water.

Section 2 Characteristics of Amphibians Chapter 40 Nervous System • The olfactory lobes are larger in amphibians than in fish. • The cerebrum is responsible for behavior and learning. • The optic lobes process information from the eyes. • The cerebellum is responsible for muscular coordination. • The medulla oblongata controls heart rate and respiration rate.

Section 2 Characteristics of Amphibians Chapter 40 Nervous System Sense Organs - • Larvae have a lateral line, most adults do not. • The eyes are covered by a nictitating membrane, a transparent moveable membrane that protects the eye. • Sound is detected by the inner ear. • Sounds are transmitted to the inner ear by the tympanic membrane, or eardrum, and the columella, a small bone that extends between the tympanic membrane and the inner ear.

Section 2 Characteristics of Amphibians Chapter 40 Anatomy of a Frog Click below to watch the Visual Concept. Visual Concept

Section 2 Characteristics of Amphibians Chapter 40 Anatomy of a Frog (part 2) Click below to watch the Visual Concept. Visual Concept

Section 3 Reproduction in Amphibians Chapter 40 Objectives • Explainhow a male frog attracts a female of the same species. • Discussthe reproductive system of a frog. • Describethe life cycle of a frog. • Describethe changes that occur during metamorphosis in frogs. • Identifytwo examples of parental care in amphibians.

Section 3 Reproduction in Amphibians Chapter 40 Courtship and Fertilization • Males attract females with a mating call. • Females only respond to males of the same species. • The male clings to the female in an embrace called amplexus. • Eggs and sperm are released into the water. • Fertilization is external.

Section 3 Reproduction in Amphibians Chapter 40 Courtship and Fertilization, continued Reproductive system • Male - includes two bean-shaped testes located near the kidneys that produce sperm during the breeding season. • Female - includes a pair of large ovaries containing thousands of tiny immature eggs. During the breeding season the eggs mature.

Section 3 Reproduction in Amphibians Chapter 40 Life Cycle • When the eggs hatch, a tadpole is released. • The tadpole grows and slowly changes from an aquatic larva into an adult in a process called metamorphosis. • Metamorphosis is controlled by a hormone called thyroxine. • Some amphibians do not produce thyroxine and remain in the larval stage their entire life. • Some amphibians do not have a larval stage and hatch from the egg as small versions of the adult.

Section 3 Reproduction in Amphibians Chapter 40 Life Cycle of a Frog

Section 3 Reproduction in Amphibians Chapter 40 Amphibian Life Cycle Click below to watch the Visual Concept. Visual Concept

Section 3 Reproduction in Amphibians Chapter 40 Parental Care Parental care increases the likelihood that the offspring will survive. • Some species guard their eggs until they hatch. • Some species sit on their eggs to prevent them from drying out. • The male Darwin’s frog carries the eggs in his vocal sacs until the larvae finish metamorphosis. • Female gastric brooding frogs swallow their eggs and the larvae mature in the stomach.

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