Abstract: The Dinosauria were the most successful land vertebrates ever, and survived for 165 million years, until most became extinct 65 million years ago. Dinosaurs first appeared about 230 million years ago, at the beginning of the late Triassic period. By the end of the Triassic period, dinosaurs dominated the then continent Pangaea, possibly contributing to the extinction of many other reptiles. Though, dinosaurs were successful, but they could not manage to survive longer after 165 million years, due to a mass extinction which happened during Cretaceous period. Sun’s solar energy is the main source of energy for sustanence of all life forms on earth. An imbalance of energy within the biological system of biosphere and non-sustenance could be possible reason for mass extinction of dinosaurs.