Dinosaurs were a diverse group of reptiles that dominated Earth for roughly 170 million years, from the Late Triassic period (around 235 million years ago) to their decline near the end of the Cretaceous period (around 66 million years ago). The term "Dinosauria" was coined in 1842 by English naturalist Sir Richard Owen, derived from the Greek words deinos meaning "fearfully great" and sauros meaning "lizard