Friday, November 2, 2007

>>Evolution and taxonomy

Evolution and taxonomy

Archaeopteryx, the earliest known bird

Archaeopteryx, the earliest known bird
The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume, Ornithologiae. Carolus Linnaeus modified that work in 1758 to devise the taxonomic classification system still in use.Birds are categorised as the biological class Aves in Linnean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda. Aves and a sister group, the order Crocodilia, together are the sole living members of the reptile clade Archosauria. Phylogenetically, Aves is commonly defined as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica.Archaeopteryx, from the Kimmeridgian stage of the Late Jurassic (some 155–150 million years ago), is the earliest known bird under this definition. Others have defined Aves to include only the modern bird groups, excluding most groups known only from fossils,in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
Modern birds all sit within the subclass Neornithes, which is divided into two superorders, the Paleognathae (mostly flightless birds like ostriches), and the wildly diverse Neognathae, containing all other birds. Depending on the taxonomic viewpoint, the number of species cited varies anywhere from 9,800 to 10,050 known living bird species in the world.

No comments: