WE HAVE KNOWN ABOUT DINOSAURS for only 150 years or so, but these great creatures roamed the Earth for 160 million years long before humans appeared. Scientists first learned about dinosaurs in the 1820s, when they discovered the fossilized bones of unknown creatures. Today, these fossils show us where dinosaurs lived, what they looked like, and what they ate. Dinosaurs were reptiles and lived on land. Their name means "terrible lizard". and like lizards, many of them had tough, scaly skin. There were hundreds of different kinds of dinosaurs, divided into two main groups. The Ornithischians (bird-hipped dinosaurs), such as Protoceratops, had hipbones similar to birds; the Saurischians (lizard-hipped dinosaurs), such as Diplodocus, had hipbones similar to lizards. Not all dinosaurs were giants - Compsognathus was the size of a chicken and Heterodontosaurus was the size of a large dog. Some dinosaurs, such as Tyrannosaurus rex, were carnivores (meat eaters); others, such as Stegosaurus, were herbivores (plant eaters). About 65 million years ago, dinosaurs and the swimming and flying reptiles that lived at the same time died out. The reason for this is still uncertain.

TYRANNOSAURUS REX 
The gigantic Tyrannosaurus was one the largest carnivorous (meat ending) dinosaurs. Scientists first discovered its fossils in North America. Tyrannosaurus measured 14 m (46 ft) in length and stood almost 6 m (20 ft) high. Its massive teeth were more than 15 cm (6 in) long. Tyrannosaurus weighed almost 7 tonnes (7 tons), so it was probably too heavy to run and hunt other dinosaurs. Tyrannosaurus fed on small creatures and dead dinosaurs.

PROTOCERATOPS

Scientists discovered fossils of Protoceratops the Gobi Desert, Mongolia, in the 1920s. The bones of adults and young were found, together with fossilized eggs. About 80 million years ago, this area was a nesting site for many families of Protoceratops.

BARYONYX fossilized claw and bones of a dinosaur were found in surrey, England. This dinosaur is named Baryonyx. fossilized scales of fish were found in this dinosaur's stomach, so it was probably a fish eater and may have used its claws to catch fish.

IGUANODON

Iguanodon was a herbivore. As an adult it was about 10 m (33 ft) long, with small hooves on its hands and feet. Some scientists believe that Iguanodon lived in herds because, in some areas of Europe, they have found many fossilized skeletons of Iguanodon together in one place

Iguanodon belonged to the bird-hipped group of dinosaurs called Ornithischians