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Explanatory Bird

This document discusses the evolution and classification of birds. It outlines that birds evolved from feathered theropod dinosaurs and the earliest known bird is Archaeopteryx lithographica. It describes the original classification system developed by Willughby and Ray in 1676 and modified by Linnaeus in 1758 which placed birds in the class Aves. Modern phylogenetic taxonomy places birds in the dinosaur group Theropoda. The document also discusses different definitions of Aves that were proposed in an effort to clarify the taxonomic classification of birds and their relationship to dinosaurs like Archaeopteryx.

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58 views1 page

Explanatory Bird

This document discusses the evolution and classification of birds. It outlines that birds evolved from feathered theropod dinosaurs and the earliest known bird is Archaeopteryx lithographica. It describes the original classification system developed by Willughby and Ray in 1676 and modified by Linnaeus in 1758 which placed birds in the class Aves. Modern phylogenetic taxonomy places birds in the dinosaur group Theropoda. The document also discusses different definitions of Aves that were proposed in an effort to clarify the taxonomic classification of birds and their relationship to dinosaurs like Archaeopteryx.

Uploaded by

SPD TIWARI
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Evolution and classification

Main article: Evolution of birds

Archaeopteryx lithographica is often considered the oldest known true bird.

The first classification of birds was developed by Francis Willughby and John Ray in their 1676
volume Ornithologiae.[3] Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system
currently in use.[4] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic
taxonomy places Aves in the dinosaur clade Theropoda.[5]

Definition
Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile
clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants
of the most recent common ancestor of modern birds and Archaeopteryx lithographica.[6] However, an earlier
definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many
scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown
group of the set of modern birds. This was done by excluding most groups known only from fossils, and
assigning them, instead, to the broader group Avialae,[7] in part to avoid the uncertainties about the placement
of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
Gauthier and de Queiroz[8] identified four different definitions for the same biological name "Aves", which is a
problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common
ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He
assigned other names to the other groups.
     
Crocodiles
     
 
Birds
 
 
Turtles
 
 
Lizards (including snakes)
 

The birds' phylogenetic relationships to major


living reptile groups.

1. Aves can mean all archosaurs closer to birds than to crocodiles (alternately Avemetatarsalia)


2. Aves can mean those advanced archosaurs with feathers (alternately Avifilopluma)
3. Aves can mean those feathered dinosaurs that fly (alternately Avialae)
4. Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a
"crown group", in this sense synonymous with Neornithes)
Under the fourth definition Archaeopteryx, traditionally considered one of the earliest members of Aves, is
removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many
researchers in the field of palaeontology and bird evolution, though the exact definitions applied have been

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