Order of
Reptile popular with the under five
crowd.
Term invented by Sir Richard Owen in 1842 to describe the "fearfully great lizards" (Greek- Deinos, "that which inspires fear and awe," and Sauros, "lizard") discovered in Europe, specifically the Megalosaurus, Iguanodon, and Hylaeosaurus. Today, mostly used to describe extinct, non-avian members of Dinosauria, which were the dominant fauna of Jurassic and Cretaceous eras (often erroneously including the contemporaneous pleisosaurs, icthyosaurs, and pterosaurs).
The first dinosaurs appeared in the Triassic, about 230 million years ago.