Amphibians Vertebrate Phylogenetic Tree Feathers Hair Amniotic egg

Amphibians

Vertebrate Phylogenetic Tree Feathers Hair Amniotic egg Four limbs Jaws

Amphibian Ancestry • Scientists believe that amphibians evolved from fishes called crossopterygians • Crossopterygians had no gills but had a primitive lung that may have enabled them to breathe for periods of time on land

Characteristics of Amphibians • Phylum Chordata (vertebrates) • Class Amphibia • Cold-blooded (cannot internally regulate temperature) • Live both on land in water • Adaptations for living on land – Still need water to keep their skin and eggs wet

Four Orders • • Anura- frogs and toads Urodela- salamanders Trachystoma- mud eels Apoda- caecilians

Reproduction • Amphibians need to return to the water to reproduce – Eggs do not have a shell to keep from drying out • Most frogs start their life as tadpoles

Metamorphosis • Change from an aquatic larval stage to a terrestrial adult • Tadpoles undergo many changes to develop into adult frogs – Gills and lungs resorbed – Tail absorbed and legs are grown – Digestive, skeletal, nervous, and circulatory systems rearranged

External Anatomy • Eye – Nictitating membrane • • • Mouth Forelimb Hindlimb Webbed foot Tympanic membraneear drum

Nictitating Membrane • A transparent eyelid that keeps the eyeball moist and protects it when it is under water

Nervous System • Brain • Spinal cord • Nerves

Digestive System • • Mouth Esophagus Stomach Small intestine Large intestine Cloaca Liver- usually largest structure, three lobes – Detox materials and produces some digestive enzymes

Circulatory System • • Heart Dorsal aorta- large blood vessel along the back Veins- carry blood back to heart Arteries- carry blood away from heart

Respiratory System • Adult frogs lose the gills but can respire in three ways: through the lungs, through the skin, and through the mouth • Respiration through the lungs is called pulmonary respiration

Excretory System • Amphibians eliminate two primary types of metabolic waste products—CO 2 from respiration and waste products from the breakdown of foods • The kidneys filter nitrogenous wastes from the blood and dilute it with water to make urine

Urogenital System

Reproductive System • Male frogs have two bean-shaped white/yellowish testes located near the kidneys

Reproductive System • Female frogs have a pair of large, lobed ovaries (curly tubes) containing thousands of tiny immature eggs lie near the kidneys

Skeletal System • The frog’s spine has nine vertebrae • The pectoral girdle connects the front legs and protects internal organs since frog has no ribs • The pelvic girdle connects hind legs