DINOSAURS

Dinosaurs were the main animals on Earth for more than 150 million years. (1)They were lizard-like reptiles. Some of them were the largest and scariest creatures ever walking on land. The word dinosaur comes from Greek words meaning “terrible lizard.”

The last dinosaurs became extinct, or died out, about 65.5 million years ago. Fossils of dinosaurs were first discovered in the early 1800s. (2) They are remains or impressions of a plant or animal that have been preserved in rock. By studying these fossils, scientists know that dinosaurs were the ancient cousins of today’s crocodiles, snakes, and lizards. Scientists also believe that today’s birds descended from dinosaurs.

Dinosaurs lived from about 245 to 65.5 million years ago. They were common during the Triassic, Jurassic, and Cretaceous geologic periods. Not all species, or types, of dinosaurs lived at the same time. (3)They also did not all become extinct at the same time. They died out gradually.

Dinosaurs lived throughout the world, and their fossils have been found on every continent. They lived in all different kinds of environments as well, ranging from tropical forests to dry, sandy deserts.

Dinosaurs were of different sizes. Some dinosaurs were smaller than a chicken. Others weighed as much as 100 tons—more than 10 times as much as the largest elephants.

Dinosaurs did not have any hair. Their skin had a bumpy or pebbly surface. Some scientists believe that dinosaurs were gray or green. These colors would have helped the dinosaurs blend in with their surroundings. Other scientists think that dinosaurs were very colorful. Bright colors would have helped males get the attention of females.

Most, if not all, dinosaurs laid eggs. Some dinosaurs built large nests to keep their babies together. Young dinosaurs grew very fast. (4)They reached full size in seven or eight years. Large dinosaurs might have lived almost 100 years.

 The last dinosaurs died out about 65.5 million years ago. Scientists still do not agree about why this happened. Some of (5)them think that dinosaurs died out because the temperature on Earth got too hot or too cold for them. Some animals lived through the time when the dinosaurs disappeared. The ancestors of today’s frogs, turtles, lizards, and snakes found a way to survive. Birds also survived. Scientists do not know why some animals lived but dinosaurs did not.