Their flat sternum is distinct from the typical sternum of flighted birds because it lacks a keel, like a raft. This structure is the place where flight muscles attach and thus allow for powered flight.[16] However, ratite anatomy presents other primitive characters meant for flight, such as the fusion of wing elements, a cerebellar structure, the presence of a pygostyle for tail feathers, and an alula on the wing.[4] These morphological traits suggest some affinities to volant groups.