Imagine walking through a prehistoric forest and coming face to face with a terrifying dinosaur. This could never have happened, of course. People and dinosaurs did not live on Earth at the same time. Dinosaurs died out long before people appeared. Dinosaurs lived from about 230 million years ago to about 65 million years ago.
HOW DO WE KNOW ABOUT DINOSAURS?
Paleontologists (scientists who study prehistoric life) learn about dinosaurs by studying fossils of their bones. These fossils are the remains of dead animals that have turned into rock.
You may have a dog for a pet at your house. Maybe you have some friends who have dogs.
No one knows how many millions of people in the world have dogs for pets. More than 1 million new purebred dogs get registered (signed up) with the American Kennel Club (AKC) each year. The AKC is the main organization for purebred dogs in the United States. A purebred is a dog whose parents and ancestors all came from the same breed of dog. A dog of mixed breeds is sometimes called a mongrel or a mutt.
What if you had to ride an elephant to school? An elephant is huge. You have to climb up on a platform to get on an elephant’s back. You might sit on the elephant’s neck and hold on with your legs. You might sit on a seat on the elephant’s back. People in Asia once rode elephants for transportation. They rode elephants into battle. They trained these intelligent animals to haul logs and do other work.
Elephants are the biggest land animals alive today. There are two species (kinds) of elephant, the African elephant and the Asian elephant. Both kinds of elephant have long trunks.
A huge bird with a white head and long, yellow claws swoops down on a river and snatches a fish right out of the water. It’s an impressive sight. So impressive that the citizens of the newly created United States of America decided to adopt the bird, the bald eagle, as their national symbol in 1782. It’s still used as a symbol—images of the eagle appear on every U.S. one-dollar bill and many quarter-dollar coins.
Since ancient times, people have thought of the eagle as a symbol of courage and power. Roman army divisions used the eagle as their symbol. The golden eagle was the symbol of the Russian and Austro-Hungarian empires and other governments in Europe.
What kind of animal can live in hot desert spring water or in the freezing water of the Antarctic? What animal can live in a shallow mud pond or the deepest part of the sea? Fish can. Antarctic icefish can live in water below 32° Fahrenheit (0° Celsius). Desert pupfish can live in water that is hotter than 100° Fahrenheit (40° Celsius).
Fish are animals that live and breathe in water. Some fish live in the fresh water of lakes and streams. Some fish live in the salt water of oceans. A few fish can live in both kinds of water.
All fishes are vertebrates (animals with backbones). Most fish have a covering of scales to protect their bodies.
KINDS OF FISH
There are about 25,000 species (kinds) of fishes. Fish come in all sizes. The huge whale shark can be 40 feet (12 meters) long. The tiny goby is only 0.4 inch (1 centimeter) long.