Home > Encyclopedia of Science > Dinosaur

• Biology of the dinosaurs
• Evidence for the existence of dinosaurs
• Words to Know
• Major groups of dinosaurs
• What became of the dinosaurs?

Dinosaurs are a group of now-extinct, terrestrial reptiles in the order Dinosauria. They lived during the Mesozoic Era, from about 225 million years ago to 66 million years ago. Species of dinosaurs ranged from chicken-sized creatures such as the 2-pound (1-kilogram) predator Compsognathus to colossal, herbivorous animals known as sauropods weighing more than 80 tons (72 metric tons). The sauropods were larger than any terrestrial animals that lived before or since.

Some dinosaurs were enormous, awesomely fierce predators, while others were mild-mannered plant eaters....