[JOAN CARTAN-HANSEN] Dinosaurs dominated the landscape for more than 160 million years - long before humans were around. The first dinosaurs lived about 230 million years ago in what is known as the Triassic period. Others came and went over the centuries finally dying out about 65 million years ago at the end of the Cretaceous period.

What we know about dinosaurs we've learned from their bones and other fossils. Scientists called paleontologists find, prepare and carefully study each new specimen. And what have they found out?

Dinosaurs started as small meat eating animals. They evolved into thousands of different types, including some of the largest animals to ever walk the earth. Dinosaurs were meat eaters and plant eaters. Some hunted their prey, others were scavengers. One way scientists can tell what kind of food a dinosaur ate is by looking at their teeth. The Tyrannosaurus or T-rex had huge teeth but it was probably a scavenger rather than a hunter.

Dinosaurs were not warm blooded or cold blooded. Rather, scientists think they were dinosaur blooded, a condition sort of like being warm blooded but not exactly. They laid eggs like birds and were good mothers, watching over their nests. Some dinosaurs ran very fast and there were avian dinosaurs that flew.

So why did dinosaurs disappear? One theory is that an asteroid hit the Earth in the Yucatan Peninsula in Mexico. The resulting explosion destroyed forests throughout most of North america and much of South America. It would have caused an earthquake and evidence of a giant tsunami has been found as far away as Spain and Brazil.

Those dinosaurs that survived the impact may well have died because their food supply was destroyed.

Not every dinosaur was wiped out. Scientists think that one sub group of the theropod dinosaurs evolved into birds.

Paleontologists continue to find and study dinosaur bones and other fossils. They're learning new things all the time taking us back to an age when dinosaurs ruled the Earth.

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