When did the dinosaurs first appear on Earth?

The oldest dinosaur types are known from rocks in Argentina and Brazil and are about 230 million years old. The most primitive of these types, Eoraptor, was a small meat-eating dinosaur. Because Eoraptor's skeleton shows some advanced skeletal features, older dinosaurs may yet be found.

The period when the first dinosaurs appeared was called the "Triassic Period." At that time, Earth was much different than it is today. There were no continents. All land was in one huge mass called, "Pangaea."

During the Triassic Period, Earth was very hot and dry. Twenty foot monsters ruled the land. This was the time when dinosaurs evolved, according to the theory of evolution.

The first dinosaur, sometimes called the "dawn dinosaur," was Eoraptor. It was about the size of a dog. An almost complete skeleton was found in Argentina in 1993. Scientists were delighted. The discovery of an almost complete skeleton of a dinosaur is a very rare find.

Eoraptor was a very fierce hunter, and a meat eater. It was fast and smart. It's teeth were serrated (sharp and jagged). It was 1 foot (12 inches) high and 3 feet (approx. 1 meter) long. It weighed only 20 lbs. (9 kilos) It stood on its hind legs and had small, grasping hands. It looked a little like a miniature t-rex. Scientists believe it could walk on four legs, but speculate (think) it did so only if necessary. The skull was small, but strong. Its bones were hollow. Eoraptor had five fingers on its front limbs, which it used with skill.

Another early dinosaur called, "Herrerasaurus" (pronounced huh-Rare-uh-Sore-us), roamed Earth at the same time as Eoraptor. It is one of three dinosaurs that were found in South America. Come back next week to learn more about Herrerasaurus.

Source from website : http://www.suite101.com/article.cfm/science_for_kids/114063