Susan Franko, age 12, of new Brunswick, ann., for tc r question:
How do amphibians differ from reptiles?
A salamander and a small lizard could be mistaken for first cousins but the little fellows are not even remotely related. They are cold blooded, backboned animals that share many other features, but the differences between them outweigh: their likenesses.
The differences between amphibians and reptiles are recorded in family trees that date back at least 200 million years. At about this time, their sea dwelling ancestors left their watery homes and tried to make a go of living on dry land. The amphibians were the first backboned animals to venture forth from their ancient seas. This bold adventure may have occurred 250 million years ago. The reptiles arrived later, about 50 million years later.
Most sea dwellers have gills for taking their oxygen from the water. When they become land dwellers, they must exchange their gills for air breathing lungs. Both amphibians and reptiles managed to perform this miracle, but the reptiles did it better. Most sea dwellers lay their eggs in the water and their infants need to swim. On land, water for the eggs and youngsters may be hard to find. The amphibians never managed to overcome this problem but the reptiles did.
Huge salamanders wallowed in the muddy swamps of the ferny forests during the carboniferous period. Some of these ancestral amphibians were seven feet long and their clammy skins needed moisture. They layed their eggs in water, and their infants went through a tadpole stage, fitted with gills to take oxygen from the water. They adapted to air breathing in easy stages. Even today, the amphibian goes through a
Complete metamorphosis and changes from a water to a land dweller. Lungs develop with time.
The ancestral reptiles had scaly skins that protected them from the drying air. They ventured farther from the water and left their eggs to hatch in the warm sand. ; then they hatched, their youngsters already had lungs. And unlike the soft toed amphibians, most reptiles developed hard, protective claws on their fingers and toes. Modern reptiles have inherited these features and they are the basic differences between the reptiles and the amphibians.
The young amphibian's need for water is, you might say, a handicap. But certain frogs, toads and salamanders manage to survive in moist hide sways, even in our arid deserts. What's more, nature has handed down a special gift from those first adventurous amphibians. The frog has lungs for breathing air and also an amazing skin for absorbing oxygen from the water.