Ratite

A ratite (/ˈrætaɪt/) is any of a group of flightless birds within the infraclass Palaeognathae. They are mostly large, long-necked, and long-legged, the exception being the Kiwi, which is also the only nocturnal extant ratite.

Our understanding of relationships within the paleognath clade have been in flux. Previously, all the flightless members 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 the 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 ('raft', a vessel which has no keel — in contradistinction to extant flighted birds with a keel). Without this to anchor their wing muscles, they could not have flown even if they developed suitable wings. Ratites are a polyphyletic 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.

Most parts of the former supercontinent Gondwana have ratites, or did have until the fairly recent past. So did Europe in the Paleocene and Eocene, from where the first flightless paleognaths are known. Ostriches were present in Asia as recently as the Holocene, although the genus is thought to have originated in Africa. However, the ostrich order may have evolved in Eurasia. A recent study posits a Laurasian origin for the clade. Geranoidids, which may have been ratites, existed in North America.