There are a lot of physical similarities between the species of ratites and these traits differ from other species not in the order. The major quality that is unique of ratites is the lack of a keel on their sternum. This causes them to be unable to fly and it is the trait that is a big reason for their classification as a separate order. Their under - developed breast muscles also are further reasoning for their lack of flight. The long strong legs of Struthioniformes are also unique to their taxonomic groups. They all lack air chambers in their legs as well. Struthioniformes also have long, lean necks which help the m reach things either underground or in the trees. One exception is the kiwi which has a long beak instead to help them reach their prey.