The word "dinosaur" combines two Greek words and means "terrible lizard." Actually, dinosaurs were not so terrible, and they definitely were not lizards. To understand how dinosaurs lived. it is important to know what they were. Tyrannosaurus is a dinosaur. So are Triceratops, Corythosouma, and Stegosaurus. But Pteranodon, a flying reptile is NOT a dinosaur.

Scientists have divided the Earth's history into large blocks of time called eras. The first is called the Paleozoic Era. Plants, insects, fish, amphibians and the first reptiles all arose during this time, which ended 248 million years ago.

Dinosaurs ruled during the Mesozoic Era. This era is divided into three periods: the Triassic, Jurassie and Cretaceous, nicknamed the Age of Dinosaurs. The Mesozoic lasted for more than 170 years and ended 65 million years ago with the extinction of the dinosaurs.

After the Mesozoic came the Cenozoic Era, otherwise known as the Age of Mammals.

#2: All dinosaurs walked full erect.

Modem reptiles like lizards and crocodiles walk with their legs sprawling out from their sides. Dinosaurs were different. They walked up off the ground, legs straight below them, just like dogs, elephants and giraffes.

#3: All dinosaurs lived on land; none had wings or paddles.

An incredible number of reptiles lived during the Mesozoic Era, and they were not all dinosaurs. Some reptiles flew and some swam. Every dinosaur discovered to date, however, was a land animal.

#4: All dinosaurs share unique features in their skeletons.

The dinosaurs are also different from other reptiles because of their skeletons. Dinosaur skulls have many openings, almost like windows. They allow the large skull to weigh less, and they hold muscles and some times special glands.
The thigh bone of most reptiles is curved, and the hips hold the legs at a sprawling angle.
Dinosaurs have a straight thigh bone, and the hip is designed to hold the legs directly under the body.