Ans - One of the most eminent groups of organisms that ruled the prehistoric landscape for millions of years were the dinosaurs. They came in all sizes and shapes, with the smallest one being comparable with that of a chicken and the largest one weighing over 77 tons. Dinosaurs wandered the earth for millions of years until the asteroid impact and the change in climate brought about their extinction. But not all dinosaurs went extinct as the birds that we see today are technically the scions of dinosaurs. They furcated off from theropods, a family of dinosaurs, which were characteristically bipedal. This is evident as all modern birds today are bipedal.