Lost dino tail keeps birds on small side

摘要

Birds are related to T. rex, one of the largest predators ever to stalk the Earth, so why are they so puny by comparison, even those that don't fly? Theropod dinosaurs, the ancestor of birds, walked with their legs vertical using their tail for balance. As their progeny evolved to fly, their tails shrank so they had to crouch to balance. This made their femurs stronger, even after some had ceased to fly.