Aves

* Aves, or birds, have a complete double circulation, oviparous, reproduction, front limbs peculiarly modified as wings; and they bear feathers. All existing birds have a horny beak, without teeth; but some Mesozoic fossil birds (Odontornithes) had conical teeth inserted in both jaws. The principal groups are: Carinatæ, including all existing flying birds; Ratitæ, including the ostrich and allies, the apteryx, and the extinct moas; Odontornithes, or fossil birds with teeth.

The ordinary birds are classified largely by the structure of the beak and feet, which are in direct relation to their habits. See Beak, Bird, Odontonithes.