The Birds World

Birds are categorised as a biological class, Aves. The earliest known species of this class is Archaeopteryx lithographica, from the Late Jurassic period. According to the most recent consensus, Aves and a sister group, the order Crocodilia, together form a group of unnamed rank, the Archosauria.

Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of modern birds (or of a specific modern bird species like Passer domesticus), and Archaeopteryx. Modern phylogenies place birds in the dinosaur clade Theropoda.

Modern birds are divided into two superorders, the Paleognathae (mostly flightless birds like ostriches), and the wildly diverse Neognathae, containing all other birds. "