Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

डायनासोर जिसका अर्थ यूनानी भाषा में बड़ी छिपकली होता है लगभग 5 varsrs वर्ष तक पृथ्वी के सबसे प्रमुख स्थलीय कशेरुकी जीव थे। यह ट्राइएसिक काल के अंत से लेकर क्रीटेशियस काल, के अंत तक अस्तित्व में रहे, इसके बाद इनमें से ज्यादातर क्रीटेशियस -तृतीयक विलुप्ति घटना के फलस्वरूप विलुप्त हो गये।