rationalskepticism.org

Extant birds do not use their femur in the same way that nonavian dinosaus did. If the chicken video were of a chicken skeleton, and a side by side gate with the T. rex skeleton were shown, the difference would be obvious. The T. rex femur could be seen to swing across a far wider arc than the femur in any extant bird. While the chicken and tyrannosaur both employ their feet in similar manners there is a subtle difference here as well. Chickens have a descended and expressed hallux (rear facing digit) which bears weight, whereas tyrannosaurs rarely left traces where this digit is seen because it is greatly reduced. This means the tyrannosaur could not easily tilt back on its feet without balance issues. Think of T. rex as being shark-like, and moving forward most of the time.

RS