The dominant terrestrial vertebrate on Earth for more than 160 million years, the dinosaurs roamed from the late Triassac period until the end of the Cretaceous period. A varied group of animals, dinosaurs numbered more than 1,000 different species. Some ate principally plants, others meat; some used two legs to move about, others four legs. Their size ranged from that of a human, or smaller, to very large. The first dinosaur fossils were recognized in the early 19th century, and have since become major attractions at museum around the world.