About Opentopia
Opentopia Directory Encyclopedia Tools

Archaeopteryx

Encyclopedia : A : AR : ARC : Archaeopteryx

Archaeopteryx (pronounced /ɑː(ɹ).kiːˈɔp.təˌɹɪks/)(Greek archaio = ancient + pteryx = wing)), from the Late Jurassic of Germany, is the earliest and most primitive known bird. Archaeopteryx was similar in size and shape to a magpie, with broad, rounded wings and a long tail. Its feathers resemble those of modern birds but Archaeopteryx was rather different from any bird known today: it had jaws lined with sharp teeth, three fingers ending in curved claws, and a long bony tail. In 1861, the discovery of the first intact specimen of Archaeopteryx, just two years after Charles Darwin published The Origin of Species, set off a firestorm of debate about evolution and the role of transitional fossils that endures to this day.

Contents

Archaeopteryx and the Origins of Birds

In the 1970s, John Ostrom argued that the birds evolved from theropod dinosaurs. Archaeopteryx provided a critical piece of this puzzle, as it preserved a number of avian features (a wishbone, flight feathers, wings, a partially reversed first toe) and a number of dinosaur and theropod features (for instance, a long ascending process of the astragalus, interdental plates, an obturator process of the ischium, long chevrons in the tail). In particular, Ostrom found that Archaeopteryx was remarkably similar to the theropod family Dromaeosauridae. Further research on dinosaurs from the Gobi Desert and China has since provided more evidence of a link between Archaeopteryx and the dinosaurs, such as Chinese feathered dinosaurs.

Archaeopteryx is probably close to the ancestry of modern birds- it shows most of the features one would expect in the ancestral bird- but it is probably not the direct ancestor of living birds.

Flight Ability of Archaeopteryx and the Evolution of Bird Flight

The feathers of Archaeopteryx were highly asymmetrical, as in the wings and tail of modern birds. This implies that the wings and tail were used for lift generation, but it is unclear whether Archaeopteryx was simply a glider, or capable of flapping flight. The lack of a bony breastbone suggests that Archaeopteryx was not a very strong flier, but flight muscles might have attached to the thick, boomerang-shaped wishbone, the platelike coracoids, or perhaps to a cartilagenous sternum.

Archaeopteryx wings were relatively large, which would have resulted in a low stall speed and reduced turning radius. The short and rounded shape of the wings would have increased drag, but could also have improved Archaeopteryx' ability to fly through cluttered environments such as trees and brush (similar wing shapes are seen in birds which fly through trees and brush, such as crows and pheasants).

In 2004, scientists analyzing a detailed CT scan of Archaeopteryx's braincase, concluded that its brain was significantly larger than that of most dinosaurs, indicating that it possessed the brain size necessary for flying. The overall brain anatomy was reconstructed using the scan. The reconstruction showed that the regions associated with vision took up nearly one-third of the brain. Other well-developed areas involved hearing and muscle coordination. (Winter, 2004) The skull scan also revealed the structure of the inner ear. The structure more closely resembles that of modern birds than the inner ear of reptiles. These characteristics taken together suggest that Archaeopteryx had the keen sense of hearing, balance, spatial perception and coordination needed to fly. (Alnso, et al., 2004)

Archaeopteryx continues to play an important part in scientific debates about the origin and evolution of birds. Some scientists see Archaeopteryx as climbing through the trees like a squirrel, following the idea that birds evolved from tree-dwelling gliders (the "trees down" hypothesis for the evolution of flight proposed by O.C. Marsh). Other scientists see Archaeopteryx as running quickly along the ground, supporting the idea that birds evolved flight by running (the "ground up" hypothesis proposed by Samuel Wendall Williston). Still others suggest that Archaeopteryx might have been at home both in the trees and on the ground, like modern crows. So far, Archaeopteryx has perhaps produced as many questions as answers, and the latest findings on this fossil are unlikely to provide the last word.

Taxonomy

The Munich Specimen
Enlarge
The Munich Specimen

The relationships of the specimens are problematic. Most specimens have been given their own species at one point or another. The Berlin specimen has been referred to Archaeopteryx siemensii, the Eichstätt specimen to Jurapteryx recurva, the Munich specimen to Archaeopteryx bavarica and the Solnhofen specimen was referred to Wellnhoferia grandis.

Recently, it has been argued that all the specimens belong to the same species (New Scientist, 17 April 2004, p.17). However, significant differences exist among the specimens. In particular, the Munich, Eichstätt and Thermopolis specimens differ from the London, Berlin, and Solnhofen specimens in being smaller, having different finger proportions and having more slender snouts, lined with forward-pointing teeth. These differences are as large as or larger than the differences seen today between adults of different bird species. However, it is also possible that these differences could be explained by different ages of the living birds.

The Fossils

Over the years, ten specimens of Archaeopteryx have been found. All of the fossils come from the limestone deposits near Solnhofen, Germany. [link]

  1. The feather: Discovered in 1860 near Solnhofen, Germany, and described in 1861 by Hermann von Meyer. Currently located at the Humbolt Museum für Naturkunde in Berlin. This is generally referred to Archaeopteryx and was the holotype for a long time, but whether it actually is a feather of this species or another, as yet undiscovered, proto-bird is unknown.
  2. London Specimen (BMNH 37001, the type specimen): Discovered in 1861 near Langenaltheim, Germany and described in 1863 by Richard Owen as Archaeopteryx macrura, assuming it did not belong to the same species as the feather. Currently located at the British Museum of Natural History in London, it is missing its head. However, this skeleton is the designated type specimen, as the 1860-61 feather cannot be identified as to species. In a subsequent edition of his Origin of Species (chap. 10, pp.335-336), Charles Darwin acclaimed Owen's discovery as linking lizard-like reptiles with modern birds.
  3. Berlin Specimen (HMN 1880): Discovered in 1876 or 1877 on the Blumenberg near Eichstätt, Germany, by Jakob Niemeyer. He exchanged this precious fossil for a cow, with Johann Dörr. It was described in 1884 by Wilhelm Dames. Currently Located at the Humbolt Museum für Naturkunde, it is the best specimen, and the first with a complete head. Once classified as a new species, A. siemensii.
  4. Maxberg Specimen (S5): Discovered in 1956 or 1958 near Langenaltheim and described in 1959 by Heller. Currently missing, though it was once exhibited at the Maxberg Museum in Solnhofen. It belonged to Eduard Opitsch, who loaned it to the museum. After his death in 1992, the specimen was discovered to be missing and may have been stolen or sold. It is composed of a torso.
  5. Haarlem Specimen (TM 6428, also known as the Teyler Specimen): Discovered in 1855 near Riedenburg, Germany and described as a Pterodactylus crassipes in 1875 by Meyer, it was reclassified in 1970 by John Ostrom. Currently located at the Teyler Museum in Haarlem, the Netherlands. It was the very first specimen, despite the classification error.
  6. Eichstätt Specimen (JM 2257): Discovered in 1951 or 1955 near Workerszell, Germany and described by Peter Wellnhofer in 1974. Currently located at the Jura Museum in Eichstätt, Germany. It is the smallest specimen and has the second best head. Possibly a separate genus, Jurapteryx recurva or species A. recurva.
  7. Solnhofen Specimen (BSP 1999): Discovered in the 1960s near Eichstätt, Germany and described in 1988 by Wellnhofer. Currently located at the Bürgermeister-Müller-Museum in Solnhofen. It was originally classified as a Compsognathus by an amateur collector. May belong to a separate genus and species, Wellnhoferia grandis.
  8. Munich Specimen (S6, formerly known as the Solnhofen-Aktien-Verein Specimen): Discovered in 1991 near Langenaltheim and described in 1993 by Wellnhofer. Currently located at the Paläontologische Museum München in Munich. Only specimen with a breastbone (sternum). May be a new species, A. bavarica.
  9. Bürgermeister-Müller Specimen: A ninth, fragmentary specimen, was discovered in 1997. A further fragmentary fossil was found in 2004. It is kept at the Bürgermeister-Müller Museum.
  10. Thermopolis Specimen Discovered in Germany. Long in a private collection, described in 2005 by Mayr, Pohl, and Peters. Donated to the Wyoming Dinosaur Center in Thermopolis, Wyoming, it has the best-preserved head and feet. The "Thermopolis" specimen, was described in the December 2, 2005 Science journal article as "A well-preserved Archaeopteryx specimen with theropod features", shows that the Archaeopteryx lacked a reversed toe—a universal feature of birds—limiting its ability to perch in trees and implying a terrestrial lifestyle. This has been interpreted as evidence of theropod ancestry. The specimen also has a hyperextendible second toe. "Until now, the feature was thought to belong only to the species' close relatives, the deinonychosaurs." [link]

Synonyms

The synonymy of A. lithographica is extremely confused. Dozens of names have been published for the handful of specimens, most of which are simply spelling errors (lapsus). Originally, the name A. lithographica only referred to the single feather described by von Meyer. Swinton (1960) proposed that the name Archaeopteryx lithographica be officially transferred from the feather to the London specimen, and the ICZN made this official in a 1961 ruling (Opinion 607).

The last 4 taxa may be valid genera and species. Also available is the genus name Archaeornis.

"Archaeopteryx" vicensensis (Anon. fide Lambrecht, 1933) is a nomen nudum for what appears to be an undescribed pterosaur.

See also

References

External links

Wikispecies has information related to:

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

Search Titles
0123456789
ABCDEFGHIJ
KLMNOPQRST
UVWXYZ?

E-mail this article to:

Personal Message: