Big Bird is a terrible example to us all, at least when it comes to bird anatomy. Check out those gams and you’ll see why. Like humans, real birds are bipedal, but their legs aren’t straight up and down. Instead, bird legs zigzag in such a way that birds are essentially in a permanent crouch, using their muscles to resist gravity. We humans don’t have to do that―our weight is borne passively on our straighter frames.
But of course, we can’t fly. The crouching posture peculiar to birds, says a recent study published in Nature, has everything to do with their evolution from dinosaur ancestors into animals capable of flight.
Previously, it was believed that the bird stance came about as a way for bird bodies to balance as massive T-Rex-style tails disappeared. Using 3-D digital reconstruction, however, the authors of the study determined that the key change was actually in the size of those adorable dinosaur arms. According to co-author John R. Hutchinson:
The tail is the most obvious change if you look at dinosaur bodies. But as we analyzed, and reanalyzed, and punishingly scrutinized our data, we gradually realized that everyone had forgotten to check what influence the forelimbs had on balance and posture, and that this influence was greater than that of the tail or other parts of the body.
Read more about the evolutionary adaptation that made bird flight possible here.