Dinosaurs are warm-blooded reptilian beasts of the class Dinosauria. They have evolved and subsequently become extinct on several planets, except for Trammis III and Ireta where they survived, and perhaps a mystery-shrouded planet where they evolved into a sapient species known as the Reptoids.
Semtor and the Thone both took Dinosaur specimens from planet Earth in the distant past; Semtor for pets and the Thone so they could make disguises patterned from them and invade Earth “silently”. Both plans backfired when Michael Peterson and 2-Tor intervened.
Dinosaurs were also hunted by Earthlings thanks to Time Safari Inc., which only targeted red-painted Dinosaurs who were going to die and had no future. In this way they avoided mucking up history until one of their customers, Eckels, stepped on a butterfly.