Numerous dinosaurs, like T. rex, had tiny arms, but paleontologists have came across that as dinosaurs progressively evolved bigger arms, they began to stand and move more like birds. Profile varies among today’s birds, with larger species like ostriches tending to have straighter legs to more economically support their own weight
Resources:
http://news.discovery.com/animals/dinosaurs/key-step-in-dinosaur-to-bird-evolution-found-130424.htm
