Classification of Modern Birds

Birds: Class Aves

Birds are bipedal, tetrapod vertebrates with feathers. Feathers alone distinguish birds from all other living vertebrates. Birds are derived from early reptiles. The avian skeleton retains many reptilian features but is highly modified for flight. The bones and feathers of the forelimb, particularly, are transformed into wings capable of powerful, flapping flight. Birds maintain a high body temperature through metabolic heat production and have a large, four-chambered heart that supports the demands of sustained activity and high metabolism.

DNA-based resolution of the phylogenetic relationships among world birds has increased dramatically in the past few years, and will continue to accelerate. Many of the latest results are available on the web as part of the Tree of Life (TOL) project.

We now have the ability to to distinguish taxa of similar rank that are reciprocally monophyletic. This lets us redefine some groups of species that in hindsight were paraphyletic. Changes in taxonomy follow, especially splitting of orders, families, and genera to create monophyletic taxa that can be reconnected to their closest relatives in the classification. These adjustments help us build a working framework for continued improvements.

In addition, DNA sequences clarify (or erase) some of the connections between the deepest historical branches of avian evolution (Hackett et al 2008). Accordingly, we can revisit the compositions of the classical Orders of birds and the relationships among them. Predictably some groups (clades) of bird species are not as closely related to each other as previously thought.

The Class Aves includes fossil groups of birds as well as modern taxa. The Subclass Neornithes includes all extant birds. The earliest divergence within Neornithes splits the Superorder Paleognathae (ratites and tinamous) and the Superorder Neognathae. In turn, the Neognathae include two primary major groups of birds. The orders of most modern birds constitute the infraclass Neoaves. The waterfowl (Order Anseriformes) and the chicken-like birds (Order Galliformes) constitute the infraclass Galloanserae.

taxon links

Following the IOC World Bird List the complete classification of modern birds is a hierarchical arrangement of 40 orders and 231 families, which include 2268 genera and over 10,496 extant species.


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