Most scientists believe that all life began in the ocean, but some of the creatures were not destined to remain in their watery home. Did you know that a fish called the lungfish is able to use its fins to walk on land? If the water where it makes its home dries up, it comes ashore and may spend months or years buried in mud until it rains. Scientists think that the amphibians evolved from a similar fish. As their fins gradually changed into legs, they became the first animals to live only part of their lives in the water. They were born with gills like the fishes, but eventually developed lungs, so that they were able to take in oxygen even after they had left the water. The only time today's amphibians have to return to the water is to lay their eggs.
Have you ever seen an amphibian? You may not think so, but if you have ever gone to a bait store and bought a salamander, caught tiny frogs as they tried to leap back into a pond, or found a toad hiding in the moist dirt in your garden, you have seen one. Although a few of the first amphibians were very small, many of them were bigger than a large dog!
No matter how hard the dinosaur hunters have tried, no one has been able to find a complete Tyrannosaurus rex skeleton. They have found enough bones to give us a good idea of what T. rex was like, but they were not all found in the same place.
Who am I?
Putting my skeleton together again would surely take a long time. My body was sometimes stretched out over 80 feet long, all the way from the tip of my tiny head to the end of my skinny tail. Who am I?
Words to Know
A reptile is a cold-blooded animal that usually lays eggs and has a backbone. Most reptiles have a scaly or tough skin. The dinosaurs that lived millions of years ago were reptiles. Snakes, lizards, crocodiles, and turtles are a few other reptiles.
These amphibians lived in a damp land that was covered with trees and ferns. Over millions of years, the plants on that land turned into the coal that provides much of our electricity today. In some places in the world, people still burn peat, a plant mixture that someday will turn into coal.
Reptile or Amphibian?
When scientists first discovered the fossils of the lizard-like animal they named Seymouria, they couldn't decide what it was. They were puzzled because it had a lateral line, which is a horizontal line on the side of the body that only amphibians and fish have. The lateral line helps the amphibians and fish find their food in the water. But if it was a water creature, why didn't it have webbed feet and why did it have teeth and claws? Eventually, they decided that this new kind of animal that looked like a reptile was actually an amphibian.