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Avialae ("bird wings") is a clade
Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
 containing bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s (Aves) and their most immediate dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
ian relatives.

ematic studies of the Avialae have produced different results depending on the specimens included and the definitions used. Including or excluding Archaeopteryx
Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
 from the group Aves has a large effect on the subgroups of Avialae. Specifically, if Archaeopteryx is defined as an avian, then there are few non-avian avialans.

Archaeopteryx
Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
 from the late Jurassic Period may be the earliest known theropod dinosaur which may have had the capability of powered flight.






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Avialae ("bird wings") is a clade
Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
 containing bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s (Aves) and their most immediate dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
ian relatives.

Competing definitions

Systematic studies of the Avialae have produced different results depending on the specimens included and the definitions used. Including or excluding Archaeopteryx
Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
 from the group Aves has a large effect on the subgroups of Avialae. Specifically, if Archaeopteryx is defined as an avian, then there are few non-avian avialans.

Archaeopteryx
Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
 from the late Jurassic Period may be the earliest known theropod dinosaur which may have had the capability of powered flight. Archaeopteryx
Archaeopteryx

Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
 is included within Avialae, and it is the avialan with the oldest reliable estimate of geological age at this time.

Character-based definition

Avialae is traditionally defined as an apomorphy-based clade
Phylogenetic nomenclature

Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to Biological classification, applying definitions from cladistics ....
 (that is, one based on physical characteristics). Jacques Gauthier
Jacques Gauthier

Jacques Armand Gauthier is a vertebrate paleontology, comparative anatomy, and systematist, and one of the founders of the use of cladistics in biology....
 named Avialae in 1986, and first defined it in 2001 as all dinosaurs that possessed feathered wing
Wing

A wing is a surface used to produce Lift for flight through the Earth's atmosphere or another gaseous or fluid medium. The wing shape is usually an airfoil....
s used in flapping flight
Bird flight

Flight is the main mode of animal locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predation....
, and the birds that descended from them.

Avialae vs. Aves
Gauthier (page 34) identified four conflicting ways of defining the term "Aves", which is a problem because the same biological name is being used four different ways. Gauthier proposed a solution, number 4 below, which is to reserve the term Aves only for the last common ancestor of all living birds and all of its descendants. He assigned other names to the other groups.

  1. Aves can mean those advanced archosaur
    Archosaur

    Archosaurs are a group of diapsid reptiles represented by modern birds and crocodilians. This group also includes extinct non-avian dinosaurs, pterosaurs and relatives of crocodiles....
    s with feathers (alternately Avifilopluma)
  2. Aves can mean those that fly (alternately Avialae)
  3. Aves can mean all reptiles closer to birds than to crocodile
    Crocodile

    A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e....
    s (alternately Panaves
    Panaves

    Panaves is a clade of advanced archosaurs coined by Jacques Gauthier in 1986. He defined it to represent the largest and most inclusive clade of archosaurs containing Aves but not Crocodylia ....
    )
  4. Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group"). (alternately Neornithes)


Under the fourth definition Archaeopteryx is an avialan, and not a member of Aves. Gauthier's restriction of Aves to modern birds has not been widely adopted in the paleontological literature.

Branch-based definition

Several authors have use a similar, but branch-based, definition; "all theropods closer to birds than to Deinonychus
Deinonychus

Deinonychus was a genus of carnivore dromaeosauridae dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 metre long dinosaur lived during the early Cretaceous Period ....
."

In 2002, Clarke and Norell used this definition in publishing a rigorously detailed phylogeny of known avialans. In their results on page 26, they organized the Avialae in successive stages of evolution, which are arranged here from most primitive at top to most advanced at bottom;

  • Dromaeosauridae
    Dromaeosauridae

    Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small to medium-sized, feathered carnivores that flourished in the Cretaceous Period ....
     is an outgroup, but a member of Avifilopluma
    • Archaeopteryx
      Archaeopteryx

      Archaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known. The name is from the Ancient Greek archaios meaning 'ancient' and pteryx meaning 'feather' or 'wing'; ....
       is the most basal Avialan
      • Confuciusornithidae
        Confuciusornithidae

        Confuciusornithidae is a Family of primitive birds from the early Cretaceous Period of China. Recognized species include Confuciusornis , Confuciusornis, Changchengornis , Jinzhouornis, Jinzhouornis, and Eoconfuciusornis, the last of which predated the other confuciusornithids by 11 million years....
         are the most basal pygostylia
        Pygostylia

        Pygostylia is a group of birds which includes Confuciusornis and all of the more derived birds; the Ornithothoraces. Chiappe defined the Pygostylia as "the common ancestor of the Confuciusornithidae and Neornithes plus all its descendants"....
        n
        • Enantiornithes
          Enantiornithes

          Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse Avialae of the Mesozoic. Almost all retained teeth and clawed hands, like other primitive birds....
           are the most basal members of Ornithothoraces
          Ornithothoraces

          Ornithothoraces is a clade of birds which includes all Enantiornithes and modern birds .The name Ornithothoraces means "bird thoraxes". This refers to a modern, highly derived, anatomy of the thorax which gave the ornithothoracines superior flight capability compared to more primitive birds....
          • Vorona
            Vorona

            Vorona is a monotypic genus of prehistoric birds. It was described from fossils found in a Maevarano Formation quarry near the village of Berivotra, Mahajanga Province, Madagascar....
            • Patagopteryx
              Patagopteryx

              Patagopteryx is an extinct monotypic genus of birds that lived during the Late Cretaceous, around 80 mya , in what is now the Sierra Barrosa in northwestern Patagonia, Argentina....
              • Apsaravis
                Apsaravis

                Apsaravis is a Mesozoic bird genus from the Late Cretaceous. The single known species, Apsaravis ukhaana, lived about 78 million years ago, in the Campanian age of the Cretaceous period....
                 is the most basal member of Ornithurae
                Ornithurae

                Ornithurae is the name of a natural group of birds coined by Ernst Haeckel in 1866.Haeckel included in the group all "true birds" with the "characteristic tail morphology of all extant birds" ....
                • Baptornis
                  Baptornis

                  Baptornis is an extinct genus of flightless bird aquatic bird from the Late Cretaceous, some 87-80 million years ago . The fossils of Baptornis advenus, the type species, were discoved in Kansas, which at its time was mostly covered by the North American Inland Sea, a shallow shelf sea....
                   + Hesperornis
                  Hesperornis

                  Hesperornis is an extinct genus of flightless aquatic birds that lived during the Santonian to Campanian sub-epochs of the Late Cretaceous ....
                  • Ichthyornis
                    Ichthyornis

                    Ichthyornis is a genus of seabird from the Late Cretaceous of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway; some fossils from other locations like Argentina and Central Asia are sometimes referred...
                    • Aves (crown group definition)


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
Epidendrosaurus

Epidendrosaurus is a genus of mid-Mesozoic maniraptoran dinosaur of the family Scansoriopterygidae. Epidendrosaurus was the first non-avian dinosaur found that had clear adaptations to an arboreal or semi-arboreal lifestyle--it is likely that it spent much of its time in trees....
 as a sister group to Archaeopteryx within Avialae. The age of the Daohugou Beds
Daohugou Beds

The Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, south of Chifeng, around Daohugou village of Ningcheng county....
 where Epidendrosaurus was collected may be Middle Jurassic
Middle Jurassic

The Middle Jurassic, called the Dogger in the European system of classification, is the second epoch of the Jurassic Period . It lasted from 176-161 million years ago....
; older than Archaeopteryx.

A study by Zhang et al. (2008) confirmed that Epidendrosaurus
Epidendrosaurus

Epidendrosaurus is a genus of mid-Mesozoic maniraptoran dinosaur of the family Scansoriopterygidae. Epidendrosaurus was the first non-avian dinosaur found that had clear adaptations to an arboreal or semi-arboreal lifestyle--it is likely that it spent much of its time in trees....
 was within Avialae and also added a new taxon, Epidexipteryx
Epidexipteryx

Epidexipteryx is a genus of small maniraptoran dinosaur, known from one fossil specimen in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing....
.

Xu et al. (2009) described Anchiornis
Anchiornis

Anchiornis is a genus of small, feathered, maniraptoran dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and dinosaurs....
, another non-avian avialan from western Liaoning
Liaoning

is a Northeast China political divisions of China of the People's Republic of China. Its one-Chinese character abbreviation is Liao ."Li?o" is an ancient name for this region, which was adopted by the Liao Dynasty which ruled this area between 907 and 1125....
, China. They found that it is the most basal
Basal

Basal is a term with several scientific meanings:*A Basal is one which forms an outgroup to a larger clade. As such the term is relative.*Basal refers to a type of insulin dosing....
, or primitive, avialan yet described. Anchiornis
Anchiornis

Anchiornis is a genus of small, feathered, maniraptoran dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and dinosaurs....
 is of uncertain Cretaceous-Jurassic age.

See also

  • Bird flight
    Bird flight

    Flight is the main mode of animal locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predation....
  • Bird
    Bird

    Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
  • Feathered dinosaurs
    Feathered dinosaurs

    The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly nonavian dinosaur fossils were discovered with preserved feathers....