Any bird species that cannot fly because its smooth, or raftlike, sternum (breastbone) lacks a keel to which flight muscles can be anchored. The group includes some of the largest birds of all time. Two extinct types, the slow-moving, heavy-bodied elephant bird of Madagascar and the moas of New Zealand, grew to 10 ft (3 m) tall. Extant ratites include the cassowary, emu, kiwi, ostrich, and rhea
The order of Struthioniformes, a diverse group of large running, flightless birds, mostly extinct, but including the cassowary, elephant bird, emu, kiwi, moa, ostrich, rhea and tinamou
flightless birds having flat breastbones lacking a keel for attachment of flight muscles: ostriches; cassowaries; emus; moas; rheas; kiwis; elephant birds