Ratitae (Emu, Rhea, Ostrich and Kiwi) are flightless birds, and having much in common with birds of flight, also have interesting differences.

Skulls have (1) Large basi-pterygoid processes developed from the basi-sphenoid. (2) Vomer is large and broad. (3) Quadrate articulates with the skull by a single, or partially divided facet.

Skeleton- Sternal keel is vestigial or absent.

Feathers-have lost the lamuli (barbules), and the vanes become no longer resistant to air and inhibit flight.