Division Odontolcae.-Marine, flightless, without sternal keel.
Dididae, flightless, recently extinct.
Flightless, wings transformed into rowing paddles.
A diagnosis covering all the Ratitae (struthio, rhea, casuarius, dromaeus, apteryx and the allied fossils dinornis and aepyornis) would be as follows - (i) terrestrial birds without keel to the sternum, absolutely flightless; (ii) quadrate bone with a single proximal articulating knob; (iii) coracoid and scapula fused together and forming an open angle; (iv) normally without a pygostyle; (v) with an incisura ischiadica; (vi) rhamphotheca compound; (vii) without apteria or bare spaces in the plumage; (viii) with a complete copulatory organ, moved by skeletal muscles.
They have spread widely, and have not confined their depredations to the rabbits, so that the indigenous flightless birds have suffered largely.