Ornithurae (meaning "bird tails" in

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

) is a natural group that includes modern

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

and their very close relatives such as the ichthyornithines and the hesperornithines. This clade is defined in the ''

PhyloCode The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...

'' by Juan Benito and colleagues in 2022 as "the smallest clade containing '' Ichthyornis dispar'', '' Hesperornis regalis'', and '' Vultur gryphus''".

Classification

Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; ; 16 February 1834 – 9 August 1919) was a German zoologist, natural history, naturalist, eugenics, eugenicist, Philosophy, philosopher, physician, professor, marine biology, marine biologist and artist ...

coined the name in 1866 and included in the group all "true birds" with the "characteristic tail morphology of all extant birds" (translation by Jacques Gauthier). This distinguishes the group from ''

Archaeopteryx ''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird'') is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaîos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...

'', which Haeckel placed in another new group called Sauriurae. Said simply, modern birds have short, fused pygostyle tails, while ''Archaeopteryx'' retained the long tail characteristic of non-avian

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s.Haeckel, Ernst (1866). ''Generelle Morphologie der Organismen''. Berlin: Georg Reimer. Gauthier converted Ornithurae into a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

, giving it a branch-based definition: "extant birds and all other taxa, such as ''Ichthyornis'' and

Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic Avialae, avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genus, genera such ...

, that are closer to extant birds than is ''Archaeopteryx''". Later he and de Queiroz redefined it as an apomorphy-based clade more in keeping with Haeckel's original usage, including the first pan-avian with a "bird tail" homologous with that of '' Vultur gryphus'', and all of its descendants.Gauthier, Jacques, de Queiroz, Kevin (2001). "Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name 'Aves'". in ''New Perspective on the Origin and Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom''. Yale Peabody Museum. Yale University. New Haven, Conn. USA They defined "bird tail" as a tail that is shorter than the femur, with a pygostyle that is a ploughshare-shaped, compressed element, with the bones fused in the adult, composed of less than six caudal vertebrae, and shorter than the free part of the tail, which itself is composed of less than eight caudal vertebrae. They included Aves (which they defined as the "

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

" of modern birds), ''Ichthyornis'', Hesperornithes, and '' Apsaravis'' in Ornithurae. Neornithes was originally proposed as a replacement for Ornithurae by Gadow in 1892 and 1893. Gauthier and de Queiroz, therefore, consider Neornithes a junior synonym of Ornithurae, though many other scientists use Neornithes to refer to the much more restrictive crown group consisting only of modern birds (a group for which Gauthier uses the name Aves). Alternately, some researchers have used Ornithurae to refer to a more restrictive node-based clade, anchored on ''Hesperornis'' and modern birds.

Relationships

The

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below is the result of a 2017 analysis by McLachlan and colleagues.

References

{{Taxonbar, from=Q3239179 Bird clades