Amphibians Section 30.2

Animal Classification Sponges Cnidarians Worms Mollusks Arthropods Echinoderms Order Anura Order Caudata Order Apoda Invertebrates Animals Fishes Amphibians Reptiles Ectotherms (cold-blooded) Amphibians Vertebrates Phylum Chordata Birds Mammals Endotherms (warm-blooded)

What is an Amphibian? Class Amphibia – means “double life” Starts life in water and changes on land Evolutionary advantages over fishes Thin, moist skin Most amphibians have four legs Lungs

What is an Amphibian? Nearly all amphibians rely on water for reproduction Undergo external fertilization Water is needed to transport sperm

Ectotherms Ectotherm – an animal that has a variable body temperature and gets its heat from external sources (can’t regulate their body temperature on their own)

Ectotherms Amphibians become dormant in regions that are too hot or cold for part of the year Many of them burrow into mud and stay there until suitable conditions return

Metamorphosis Tadpoles possess fins, gills, and a two-chambered heart as seen in fish Tadpoles develop legs, lungs, and a three-chambered heart to become adults

Metamorphosis Young salamanders resemble adults, and they have gills and usually have a tail fin Most adult salamanders lack gills and fins Adult salamanders have no lungs and breathe only through their skin

Walking Requires More Energy The evolution of the three-chambered heart in amphibians ensured that cells received the proper amount of oxygen

Walking Requires More Energy One chamber receives oxygen-rich blood from the lungs and skin Another chamber receives oxygen-poor blood from the body tissues Blood from both chambers then moves to the third chamber which mixes the two types of blood

Walking Requires More Energy Because of the mixture of blood, the skin is much more important than the lungs as an organ for gas exchange

Walking Requires More Energy Because the skin of an amphibian must stay moist to exchange gases, most amphibians are limited to life on the water’s edge or other moist areas

Frogs and Toads Frogs and toads belong to the order Anura Frogs have long hind legs and smooth, moist skin Toads have short legs and bumpy, thick, dry skin

Frogs and Toads Adult frogs and toads are predators that eat invertebrates, such as insects and worms Many species of frogs and toads secrete chemicals through their skin as a defense against predators Frog eating bird

Frogs and Toads Frogs and toads also have vocal cords Vocal cords – sound-producing bands of tissue in the throat As air moves over the vocal cords, they vibrate and cause molecules in the air to vibrate

Frogs and Toads Tympanic membrane – amplifies sounds frogs and toads make Throat pouches and tympanic membranes increase the loudness of their calls

Frogs and Toads Frogs and toads are among the first organisms to be exposed to pollutants in the air, on land, or in the water Declining numbers of frogs species sometimes indicate the presence of pollutants in the environment

Salamanders A salamander (order Caudata) has a long, slender body with a neck and tail Salamanders resemble lizards, but have smooth, moist skin and lack claws

Salamanders The young hatch from eggs, look like small salamander adults, and are carnivorous

Caecilians Caecilians (order Apoda) are burrowing amphibians, have no limbs, and have a short (or no) tail They are tropical animals with small eyes that often are blind

Caecilians They eat earthworms and other invertebrates found in the soil All caecilians have internal fertilization

Challenges of Life on Land Some dangers living on land 1. Temperature of water remain fairly constant while air temperatures can vary greatly

Challenges of Life on Land 2. Without the support of water, the body was clumsy and heavy The legs of a salamander are set at right angles to the body. This prevent the belly from dragging on the ground.

Challenges of Life on Land Raised trunks from the ground increases mobility