The Ratites are terrestrial. As time went by their ancestors, which were able to fly, adapted to using their legs as the main form of locomotion. Eventually the wings lost their usefulness for flight and evolved to serve other purposes. The living birds in this group have wings too small to lift their weight, which in some of them is considerable. Included in the Ratites are the largest birds alive.

As a consequence of evolution, the internal anatomy also went thru some changes. One of them was the breastbone becoming flat, opposed to a keel.

In this superorder are also grouped the Tinamous, which present a very interesting case in evolution. The breastbone is in the form of a keel and they are able to fly. Some authors believe they are very “primitive” ratites which still have not lost the capability of flight; others prefer not to call them ratites.