>>47735
But how similar their build? T-rex leg is more similar to dogs' I think. They have long femur while the birds in question a short one and their ankle looks like as if it was a backward bending knee. Plus they are missing the long heavy tail which balances the heavy head of the t-rex.
I dunno somewhat similar, but for me there are lots of differences.
Still arms can have many functions, and one of them is balancing for many animals, even for humans as you pointed out.