Avialae

Avialae ("bird wings") is a clade of archosaurian vertebrates containing the only living branch of dinosaurs, the birds (class Aves), and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds than to deinonychosaurs, though alternative definitions are occasionally used (see below). Archaeopteryx lithographica, from the late Jurassic Period Solnhofen Formation of Germany, is usually considered the earliest known avialan which may have had the capability of powered flight; a minority of studies have suggested that it might have been a deinonychosaur instead. Several older (but non flight-capable) possible avialans are known from the late Jurassic Tiaojishan Formation of China, dated to about 160 million years ago.

Avialae ("bird wings") is a clade of archosaurian vertebrates containing the only living branch of dinosaurs, the birds (class Aves), and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds than to deinonychosaurs, though alternative definitions are occasionally used (see below). Archaeopteryx lithographica, from the late Jurassic Period Solnhofen Formation of Germany, is usually considered the earliest known avialan which may have had the capability of powered flight; a minority of studies have suggested that it might have been a deinonychosaur instead. Several older (but non flight-capable) possible avialans are known from the late Jurassic Tiaojishan Formation of China, dated to about 160 million years ago. Aves can mean all reptiles closer to birds than to crocodiles (alternatively Avemetatarsalia [=Panaves]) Aves can mean those advanced archosaurs with feathers (alternatively Avifilopluma) Aves can mean those feathered dinosaurs that can fly (alternately Avialae) Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group"). (alternatively Neornithes) Under the fourth definition Archaeopteryx is an avialan, and not a member of Aves. Gauthier's proposals have been adopted by many researchers in the field of paleontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is sometimes used synonymously with the vernacular term "bird" by these researchers. ==References==

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