In recent years, there has been an increasing number of dinosaur bones discovered in more and more places around the world. The evidence discovered in the bones tells us that the various dinosaurs we have discovered are not all closely related to one another. Generally, they have evolved along two parallel lines. The differences seen in their arrangement of the teeth in the jaws, as well as the number of hip bones tell us that there have been two main kinds of dinosaur. Each of these kinds includes dinosaurs that used to walk on their hind legs and dinosaurs walked on all fours. The kind that walked on hind legs (and were carnivores) is referred to as the Theropoda, while the latter is called the Sauropoda (plant eaters).

The flesh eating dinosaurs were found to have sharp teeth with edges filed like those on a saw. These dinosaurs usually ran on their hind legs to catch prey, with their bodies bent forward and their tails outstretched in order to keep their balance. Their feet usually had three or more toes, but only left three toe imprints on the ground when they ran. Some of these footprints of even been mistaken for those of prehistoric birds, but they are generally deeper and larger. 225 million years ago, these carnivores began to rapidly grow in size and adapted a more terrifying appearance. Some species could grow up to 4 feet long but maintained their agility in order to quickly search for food. The skeletons found in Europe showed lighter and faster dinosaurs than those found in North America. In American sites, skeletons of flesh eaters were found to have developed cruel-looking claws on their hands and feet, proving that these species had already developed the capability to tear their enemies into shreds.

In the next geological age, dinosaur flesh eaters grew more and more terrifying and impressive, culminating in the age of the Tyrannosaurus Rex, or "tyrant lizard". It was a lizard that had a head over 6 feet long and was nearly 50 feet long overall. The T. Rex, as it is more popularly called, had a short neck and a massive body. Its four legs were very feeble and its hands are reduced to two little fingers. While it did not have speed or wits, the T. Rex could easily claw their prey into sheds by their sheer weight, the strength of their heavy jaws and merciless 6 inch teeth. Most T. Rexes were estimated to have weighed nearly 10 tons. That's very heavy, considering that a large African bull elephant weighs only 7 tons. Skeletons of the T. Rex have been found in many continents and especially large numbers have been found in the territory of the former Soviet Union.

At about the same time as the Rex, several skeletons have been found to suggest that other flesh eaters of the same caliber lived around the margins of the lakes or bodies of water. These lesser-known reptiles were called the Plateosaurus. They had massive feet with five toes and their footprints have been found all over the United States, especially in Texas. They were probably also some of the largest animals that have ever existed, towering over the T. Rex at times.

Another popular dinosaur, the Brontosaurus or "thunder lizard" lived at about the same time as well. It had a small head like a horse's, a body that was like an elephant's and a very long tail with massive legs. These animals must've easily weighed around 30 or 40 tons. We would naturally ask how could such large animals move around. Well, most of their mobility is attributed to the fact that these dinosaurs spent a lot of time living in water, whose buoyancy ease the great burden off their feet. At the same time, it could be surrounded by water as protection from other flesh eating rivals.

Many remains of these popular dinosaurs have been found all over the United States, especially in Colorado and Utah. Most of the giant dinosaurs lived in the days of the Jurassic period and more and more of their skeletons are excavated from South America, Australia and India.