At 7 feet long and 3 feet tall, Beipiaosaurus is one of the largest known feathered theropods--the group of swift upright dinosaurs from birds are thought to be descended. For a long time, scientists didn't know how to classify Beipiaosaurus because it shared characteristics more commonly found among plant eating dinosaurs. It lived about 125 million years ago and had a toothless beak, cheek teeth that it used to chew plants and the beginnings of a bulging pot belly. But theropods are the only group of dinosaurs so far known to have feathers, and many scientists take Beipiaosaurus's feathers as evidence for it being a theropod.