Dinosaurs were vertebrate animals that dominated terrestrial ecosystems for over 160 million years, first appearing approximately 230 million years ago. At the end of the Cretaceous Period, approximately 65 million years ago, a catastrophic extinction event ended dinosaurs' dominance on land. One group of dinosaurs is known to have survived to the present day: taxonomists consider modern birds to be direct descendants of theropod dinosaurs. ************************************** Since the first dinosaur fossils were recognized in the nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular among children and adults alike. They have been featured in best-selling books and films, and new discoveries are regularly covered by the media. **************************************** The term dinosaur is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although technically none of these were dinosaurs.