A ratite is any of a diverse group of large, flightless birds of the infraclass Palaeognathae. The systematics involved have been in flux. Some sources state that ratites include all the flightless birds of the Palaeognathae; previously, all these birds had been assigned to the order Struthioniformes, which is more recently regarded as containing only the ostrich. The modern bird superorder Palaeognathae consists of ratites and flighted Neotropic tinamous (compare to Neognathae). Unlike other flightless birds, the ratites have no keel on their sternum – hence the name from the Latin ratis (for raft). Without this to anchor their wing muscles, they could not fly even if they were to develop suitable wings. Recent research has indicated that ratites are a paraphyletic group; tinamous fall within them, and are the sister group of the extinct moa. This implies that flightlessness is a trait that evolved independently multiple times in different ratite lineages.