Dinosaurs are a group of reptiles that have lived on Earth for about 245 million years. They first appeared during the Triassic period, between 245 and 233.23 million years ago, and became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 million years ago. Dinosaurs are archosaurs, a larger group of reptiles that first appeared about 251 million years ago, near the start of the Triassic Period. Some other non-dinosaur reptiles are also archosaurs, including pterosaurs (the now-extinct flying reptiles) and modern crocodiles and their ancestors.
Key facts about dinosaurs include:
- Dinosaurs evolved diverse shapes and sizes, from the fearsome giant Spinosaurus to the chicken-sized Microraptor, and were able to survive in a variety of ecosystems.
- All non-avian dinosaurs went extinct about 66 million years ago.
- There are roughly 700 known species of extinct dinosaurs.
- Dinosaur fossils have been found on all seven continents.
- The word "dinosaur" means "terrible lizard" in Greek, and it was coined in 1842 by Sir Richard Owen, an English Professor of Comparative Anatomy and Physiology.
It is important to note that not all prehistoric reptiles are dinosaurs. Marine reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs, are not dinosaurs, nor is Dimetrodon or other reptiles in the same group (previously called mammal-like reptiles' and now called synapsids) .
