Common ostrich other members of Palaeognathae and thus the flighted tinamous are the sister group to the extinct moa. It is distinctive in its appearance, with a long neck and legs, and can run for a long time at a speed of or even up to about , the fastest land speed of any bird. The common ostrich is the largest living species of bird and lays the largest eggs of any living bird (extinct elephant birds of Madagascar and the giant moa of New Zealand laid larger eggs). The common ostrich's diet consists mainly of plant matter, though it also eats
Largest prehistoric animals gruiform and largest phorusrhacid or "terror bird" (highly predatory, flightless birds of South America) was "Brontornis", which was about tall at the shoulder, could raise its head above the ground and could have weighed as much as . The immense phorushacid "Kelenken" stood tall with a skull long ( of which was beak), had the largest head of any known bird. The largest North American phorusrhacid is "Titanis", which is about tall, as tall as a forest elephant. The largest-known bird of prey ever was the enormous Haast's eagle ("Harpagornis moorei"), with a wingspan of , relatively short for their