for over 160 million years, from the late Triassic period about 225 million years ago to the end of the Cretaceous period about 65 million years ago, when most of them became extinct during a large-scale extinction of animals and many varieties of plants in a relatively short geological period of history. Fossil remains of dinosaurs found on all continents. Now paleontologists described more than 500 different genera and more than 1,000 different species, which are clearly divided into two groups: the ornithischian and saurischian dinosaurs.