II. Sub-class Neornithes.—Metacarpals fused. Second finger the longest. Not more than thirteen caudal vertebrae.
I. Division Ratitae.—Terrestrial, flightless. Without sternal keel. Quadrate bone with single proximal knob. Without pygostyle. Coracoid and scapula fused. Compound rhamphotheca. Adult without apteria. With copulatory organ. A collective polyphyletic or heterogeneous group, originally cosmopolitan; with certainty existing since the Miocene.
1. Order Struthiones.—With pubic symphysis. Two toes only, third and fourth. Struthio, ostrich, Pliocene of Samos and of north-west India, now Africa and Arabia.
2. Order Rheae.—With long ischiadic symphysis. Three toes. Mesembriornis, Miocene or Pliocene of Argentina. Rhea, South America.
3. Order Casuarii.—Three toes. Aftershaft as long as the other half. Casuarius and Dromaeus, Australian. Hypselornis, Pliocene of Sivalik Hills.
4. Order Apteryges.—Four toes. Bill long and slender. Apteryx, New Zealand.
5. Order Dinornithes.—Three or four toes. Bill short. Anterior limbs extremely reduced. Dinornis, numerous species, recently extinct, New Zealand.
6. Order Aepyornithes.—Aepyornis, recently extinct, Madagascar.
To the Ratitae belong possibly also the imperfectly known Diatryma, Eocene of New Mexico, Gastornis and Dasornis, Eocene of Europe, Genyornis, Pleistocene of Australia.