30.2 Amphibians

What is an Amphibian? The class Amphibia transitions from a completely aquatic larva to an air-breathing , semi terrestrial adult Includes three orders Caudata: salamanders and newts Anura: frogs and toads Apoda: legless caecilians

Characteristics: Thin, moist skin Four legs No claws on toes External fertilization

Amphibians are ectotherms An ectotherm is an animal in which the body temperature changes with the temperature of its surroundings Become dormant in regions that are too hot or cold for part of the year

Amphibians undergo metamorphosis Fertilized eggs hatch into tadpoles Possess fins gills, and two-chambered heart Develop legs, lungs, and three-chambered heart as they grow into adults

Walking requires more energy In the three chambered heart: One chamber receives oxygen-rich blood from the lungs and skin Another chamber receives oxygen-poor blood from the body tissue Blood from both chambers moves into the third chamber Pumps oxygen-rich blood to body tissues Pumps oxygen-poor blood back to lungs and skin Results in some mixing Skin is an important means of exchanging gases Must stay moist

Diversity of Amphibians Frogs and toads belong to the order Anura No tails Frogs: long hind legs smooth moist skin Toads: Short legs Bumpy dry skin

Many secrete chemicals through skin as a defense Have vocal chords Both: Have jaws and teeth Eat insects Many secrete chemicals through skin as a defense Have vocal chords Sound producing bands of tissue in the throat As air moves over it, they vibrate

Salamanders belong to the order Caudata Long slender body with a neck and tail Resemble lizards but have smooth moist skin and lack claws Newts are salamanders that live entirely in water

Caecilians are limbless amphibians Have no limbs Short, or no tail Primarily tropical animals with small eyes Eat invertebrates in the soil

Origins of Amphibians Challenges of life on land Air temperatures vary greatly Without the support of water the body was clumsy and heavy Amphibians probably evolved from an aquatic tetrapod around the middle of the Paleozoic Era Survived and dominated because of ability to breathe through their lungs, gills, or skin