Avialae

Avialae ("bird wings") is a clade of dinosaurs containing their only living representatives, birds (Aves), and the most immediate extinct relatives of birds.

Competing definitions

Systematic studies of the Avialae have produced different results depending on the specimens included and the definitions used. Including or excluding Archaeopteryx from the group Aves has a large effect on the subgroups of Avialae. Archaeopteryx, from the late Jurassic Period, may be the earliest known theropod dinosaur which may have had the capability of powered flight. If Archaeopteryx is defined as an avian, then there are few non-avian avialans.

Character-based definition

Avialae is traditionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier named Avialae in 1986, and first defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.

Avialae vs. Aves

Gauthier

The cladogram below follows the results of a phylogenetic study by Gao and colleagues in 2002. Note that these authors used the more inclusive, node-based definition of Aves. The placement of scansoriopterygids follows Zhang et al., 2008.

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Non-Avian Avialans

There are three taxa that are not members of Aves, but are avialans, in any definition of Avialae listed above.

Senter (2007) placed Epidendrosaurus as a sister group to Archaeopteryx within Avialae. The age of the Daohugou Beds where Epidendrosaurus was collected may be Middle Jurassic; older than Archaeopteryx. A study by Zhang et al. (2008) confirmed that Epidendrosaurus was within Avialae and also added a new taxon, Epidexipteryx.

==References==

See also

Bird flight

Bird

Feathered dinosaurs