One is an ostrich, the other is a mononykus dinosaur. The structural relationship is obvious. Mononykus moved about on two legs, was very nimble, and could run at high speeds, something that would have been useful in the open desert plains where they lived. It had a small skull, and its teeth were small and pointed, suggesting that it ate insects and small animals, such as lizards and mammals.
Birds are to be believed to have evolved from bipedal dinosaurs called theropods around 150m years ago.