Amphibians
1. Amphibians are ectothermic vertebrates.
2. Their skin lacks scales, hair, and feathers, and is either smooth (like a frog) or rough (like a toad). They are dependent upon moisture and subject to desiccation; their skin must remain moist to aid in breathing.
3. They lay eggs in water, which hatch into an intermediate life form (tadpole or larva) that usually breathes with gills, and change into the adult form that breathes air and can live outside water.
4. They have three-chambered hearts.
5. They lack claws on their toes.
You already knew all the facts that are in bold, didn't you? Let's think of the various kinds of amphibians that Cazadero has, and you can probably figure out all the characteristics of the class. The frog at the top is the Pacific treefrog, one of the most famous frogs in the world. Do you know why? It is the frog heard round the world! Most Hollywood movies have used the croaking of Pacific treefrogs when they want frog noises, because they are champion croakers. They are treefrogs, so they do not spend much of their time in water, but are found in trees.
The toad (below, left) is the Western Toad, which you can find in the thousands down by Austin Creek in later summer when they have hatched out from their tadpole stage. The amphibian (below, right) is the California Newt. Newts are like salamanders, but they have the rougher, dryer skin like a toad. Frogs are like salamanders, and toads are like newts. They all have moist skins, through which they can breathe (they also have lungs for breathing).The salamander at the bottom is the California Slender Salamander, which is about 3 inches long but only 1/4 inch wide.
The name "amphibian" comes from the Latin for "two lives", which refers to the fact that all amphibians have a larval stage (we call the larval stage of frogs and toads a "tadpole" or "pollywog") and an adult stage. This is unique in the vertebrate world, because fish, reptiles, birds, and mammals are all born as small versions of the adult, not a completely different form. This dual life, one aquatic with gills and one terrestrial with lungs, may be representative of the evolution of animals out of water and onto dry land.
Now, lets look at the characteristics of the class amphibian. You already knew that frogs were cold-blooded if you ever picked one up. You also knew that tadpoles hatched into frogs, and that frogs do not have feathers, scales, or hair ("fine as frog fur" is a famous phrase), and that their skin was moist. You probably already knew that frogs lay eggs. So you are already an expert on what makes an amphibian an amphibian! The other characteristics may be fun to know, but you can classify an animal as an amphibian just by what you already know.
Frogs, toads, salamanders, and newts are all amphibians because they are cold-blooded, have no scales, hair, or feathers, their skin is moist, they lay eggs in water, and their life cycle has two stages, the "pollywog" or larval stage and the adult stage.
