
The Archaeornithes, classically Archæornithes, is an extinct group of the first primitive, reptile-like
birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
. It is an
evolutionary grade
A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.
Definition
An evolutionary grade is a group of s ...
of
transitional fossils
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross a ...
, the primitive birds halfway between non avian
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
ancestors and the derived modern birds (avian dinosaur).
Fossils
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
of early birds were poorly known until the late 20th century. Of those known, all fell into either the relatively modernly built birds with fused ribcage and the
breastbone
The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury ...
extended into a
keel
The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in B ...
, or the "
Urvogels" of the
Solnhofen Plattenkalk of late
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
age. As the physiological and anatomical difference between the two was so great, the subclass Archaeornithes was erected for the latter.
With the unearthing of several well preserved early bird fossils in the last decades of the 20th century and early 21st century, our knowledge of the evolution of birds has increased dramatically.
The evolution of the modern avian traits such as the compact body, clawless wing and the
alula
The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive of ''ala'', meaning "wing". The ...
are now known to appear over successive stages. Today the Archaeornithes are classified into a series of nested
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...
groups, and the name is rarely used in modern literature.
Classification
In traditional classification, it is one of two
subclasses
Subclass may refer to:
* Subclass (taxonomy), a taxonomic rank below "class"
* Subclass (computer science)
* Subclass (set theory)
See also
* Superclass
{{disambiguation ...
of birds, the other subclass being the
Neornithes
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
, the birds with a short, modern tail. This classification was erected by
Hans Friedrich Gadow in 1893 and followed by
Alfred Romer
Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution.
Biography
Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
(1933) and subsequent authors through most of the 20th century.
Other
mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...
birds like the toothed, but otherwise modern, birds like ''
Hesperornis'' were included under the latter in their own superorder, the
Odontognathae 230px, Ichthyornis skeletons
Odontognathae is a disused name for a paraphyletic group of toothed prehistoric birds. The group was originally proposed by Alexander Wetmore, who attempted to link fossil birds with the presence of teeth, specifical ...
.
According to
Romer
A Reference Card or "Romer" is a device for increasing the accuracy when reading a grid reference from a map. Made from transparent plastic, paper or other materials, they are also found on most baseplate compasses. Essentially, it is a specia ...
, the Archaeornithes are characterised by having clawed wings, a reptilian style ribcage without a large
carina and the presence of a long, bony tail.
The known members of the group by the time of its erection were ''
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 (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'' and ''Archaeornis''.
The two are now thought to represent a single species, ''Archaeopteryx lithographica'', the ''Archaeornis'' being the Berlin specimen of ''Archaeopteryx''.
The
Confuciusornithidae and
Enantiornithes
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cl ...
were found a century after Gradow's organization of birds into two subclasses. They fall between Romer's description of Archaeornithes and Neornithes, in that they have clawed wings, but reduced tails with a rod-like pygostyle (as opposed to the
ploughshare-shaped one in modern birds) and the presence of a small carina.
While rarely used by palaenthologists today, the term was revived by the
ornithologists Livezey and Zusi in 2007, for a group comprising
Archaeopterygidae and the
Confuciusornithidae.
See also
*
Sauriurae
*
Evolution of birds
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
References
{{Reflist , refs =
[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]
[Livezey, B.C. & Zusi, R.L. (2007): Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. '']Zoological Journal of the Linnean Society
The ''Zoological Journal of the Linnean Society'' is a monthly peer-reviewed scientific journal covering zoology published by Oxford University Press on behalf of the Linnean Society. The editor-in-chief is Maarten Christenhusz (Linnean Society). ...
'' no 149(1), pp 1-95
[{{cite web, title=Archaeornithes, url=http://www.merriam-webster.com/dictionary/archaeornithes, work=Merriam-Webster online dictionary, publisher=www.merriam-webster.com, accessdate=14 October 2011]
[{{aut, Monastersky, R. (1996): Evolution's fast track toward slow flight. '']Science News
''Science News (SN)'' is an American bi-weekly magazine devoted to articles about new scientific and technical developments, typically gleaned from recent scientific and technical journals.
History
''Science News'' has been published since ...
'' 150(5): 71
PDF fulltext
/ref>
[''Archaeopteryx'' turns out to be singular bird of a feather. '']New Scientist
''New Scientist'' is a magazine covering all aspects of science and technology. Based in London, it publishes weekly English-language editions in the United Kingdom, the United States and Australia. An editorially separate organisation publish ...
'' 2443:17. 17 April 2004
See commentary on article
[ Romer, A. S. & Parsons, T. S. (1985): ''The Vertebrate Body.'' (6th ed.) Saunders, Philadelphia.]
[{{cite book, last=Romer, first=A.S., title=]Vertebrate Paleontology
Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord. It also tries to connect, by us ...
, publisher=University of Chicago Press, year=1933, 3rd ed., 1966.
External links
Archaeornithes at the Paleobiology Database
Jurassic birds
Vertebrate subclasses