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Subclade Archosauria: Avemetatarsalia to Neornithes 

Taxon Feedback
Taxon Aves 
Nominal Author Linnaeus 1758 
2° Nominal Author  
Taxon Status active
Comments The eight distinct phylogenetic definitions that have been generated for the taxon Aves can be subdivided into two basic approaches: (1) restricting Aves to crown-clade birds (as a replacement for Neornithes) or (2) maintaining more inclusive taxonomic content anchored on the extinct taxon Archaeopteryx lithographica. The second approach recognizes what might be termed a “traditional” Aves and is preferred here because justification for globally repositioning commonly-used taxa is regarded as flawed (Sereno 1998, 2005). The dual use of Aves is likely to persist for some time. A crown clade definition for Aves was first proposed by Gauthier (1986) and later revised by Gauthier & de Queiroz (2001). Arguing that this is a better match to the original use of the name by Linnaeus, they set aside the last 150 years of modern taxonomy during which Aves was applied to living birds plus their fossil antecedents. Gauthier (1986) replaced this traditional concept of Aves with Avialae, although the phylogenetic definitions of these two taxa differ—one node-based and the other stem-based. They are not synonyms. Gauthier (1986:36) explicitly defined Avialae as a stem-based taxon including all taxa closer to birds than to Deinonychosauria. Subsequently, Gauthier and de Queiroz (2001:25-26) claimed that Gauthier (1986) really did not define Avialae. They proposed a form-qualified (“apomorphy-based”) definition based on the presence of “feathered wings . . . used for powered flight,” a definition that ranks among the most ambiguous (Sereno 2005). Gauthier (1986:36), nevertheless, was very explicit in formulating a stem-based definition for this taxon. More recently, Clarke (2004) unwittingly proposed a new node-based definition for Avialae, attributing it in error to Gauthier (1986). Ironically, Clarke’s new definition now identifies the same node-based clade that many of us would like to continue to reserve for Aves. This second option follows another tradition dating back 150 years to the discovery of the basal bird Archaeopteryx lithographica. Three similar node-based definitions were proposed independently in the same year by Sereno (1997, 1998), Chiappe (1997) and Padian (1997). All used Archaeopteryx to anchor the definition but sampled more derived birds in different ways (Passeriformes, extinct birds, extant birds). The active definition is a first-order revision that uses Archaeopteryx lithographica and Passer domesticus as specifiers.  
Potential Synonomy  

Active Phylogenetic Definition Feedback
Active Definition The least inclusive clade containing Archaeopteryx lithographica Meyer 1861 and Passer domesticus (Linnaeus 1758). 
Shorthand < Archaeopteryx lithographica and Passer domesticus
Definitional Author Sereno 2005 
Definition Status original
textual substitution
first-order revision
second-order revision
Definition Type node
Node-Stem Triplet yes
Other Triplet Taxa Ornithurae, Archaeopterygidae 
Specifier A Archaeopteryx lithographica 
Specifier(s) B Passer domesticus 
Specifier(s) C  
Taxonomic Content stem (entirely extinct)
crown (extant-bounded)
mixed (extant/extinct-bounded)
Publication Year 1997 

Inactive Taxon Status Feedback
Rejection Criteria junior synonym
historically polyphyletic
incomplete definition
no definition

Current Age Range Feedback
Earliest Record Kimeridgian (156 Ma) 
Latest Record Recent 
Range (My) 156 
Basis for Range Archaeopteryx lithographica, from the Kimmeridgian of Germany (Padian 2004), stands as the earliest record for Aves. Dates are rounded to the nearest million, the earliest from the beginning of the stage and the latest from the end of the stage (Gradstein et al. 2004). 

Definitional History #1
Definition 1 All descendants of the most recent common ancestor of Ratiti, Tinami, and Neognathae. 
Author Gauthier 1986:14 
Type node  stem 
Specifiers Ratitiae, Tinamidae, Neognathae 

Definitional History #2
Definition 2 Archaeopteryx, Passeriformes, and their common ancestor and all descendants. 
Author Sereno 1997:459 
Type node  stem 
Specifiers Archaeopteryx, Passeriformes 

Definitional History #3
Definition 3 Archaeopteryx plus extinct birds and all descendants of their most recent common ancestor. 
Author Chiappe 1997:32 
Type node  stem 
Specifiers Archaeopteryx, extinct birds 

Definitional History #4
Definition 4 Archaeopteryx, extant birds, and all descendants of their most recent common ancestor. 
Author Padian 1997:39 
Type node  stem 
Specifiers Archaeopteryx, extant birds 

Definitional History #5
Definition 5 Archaeopteryx, Neornithes, their most recent common ancestor and all descendants. 
Author Sereno 1998:65 
Type node  stem 
Specifiers Archaeopteryx, Neornithes 

Definitional History #6
Definition 6 The crown clade stemming from the most recent common ancestor of Ratitae (Struthio camelus Linnaeus 1758), Tinamidae (Tetrao [Tinamus] major Gmelin 1789), and Neognathae (Vultur gryphus Linnaeus 1758). 
Author Gauthier and de Queiroz 2001:29 
Type node  stem 
Specifiers Struthio camelus, Tetrao [Tinamus] major,Vultur gryphus 

Definitional History #7
Definition 7 All taxa phylogenetically bracketed by Archaeopteryx and Ornithurae. 
Author Senter et al. 2004:19 
Type node  stem 
Specifiers Archaeopteryx, Ornithurae 

Definitional History #8
Definition 8 The last common ancestor of all living birds and all of its descendants.  
Author Clarke 2004:18 
Type node  stem 
Specifiers all living birds