Dinosaurs are a diverse group of reptiles that belong to the clade Dinosauria, first appearing in the Triassic period around 243 to 233 million years ago. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event and thrived throughout the Jurassic and Cretaceous periods. Birds, which evolved from theropods, are considered avian dinosaurs and are the only lineage that survived the Cretaceous–Paleogene extinction event about 66 million years ago.
Dinosaurs exhibit great variation in taxonomy, morphology, and ecology, with over 900 genera and more than 1,000 species of non-avian dinosaurs identified. While birds are generally small, many prehistoric dinosaurs were large, with some sauropods reaching lengths of up to 39.7 meters (130 feet). The idea that all non-avian dinosaurs were gigantic is a misconception, as many were quite small.
The term “dinosaur,” meaning “terrible lizard,” was coined by Sir Richard Owen in 1842. Since then, dinosaur fossils have become major attractions in museums and have deeply influenced popular culture, leading to significant funding and research in the field.
