Archaeopteryx: Encyclopedia - Archaeopteryx

Archaeopteryx

Archaeopteryx lithographica (ahr-kee-OP-ter-ix) meaning "ancient wing", because it resembled an ancient bird (Greek archaio = ancient + pteryx = wing), refers to a Jurassic fossil with both bird and dinosaur features, and is widely accepted as the earliest and most primitive known bird. The discovery of the first intact specimen in 1861, 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.

Over the years, ten specimens of Archaeopteryx have been found. "All ten fossils were found in a limestone deposit near Solnhofen, Germany." [1] The fine-grained limestone, which preserves detailed casts of features not often fossilized, is used by artists and printers for lithographic plates, thus the species name lithographica.

In the 1990s, the discovery of a number of well-preserved feathered dinosaurs in China solidified the link between dinosaurs and birds.

Archaeopteryx - Primitive bird

Archaeopteryx was similar in size and shape to a magpie, with short, broad wings and a long tail. The feathers resemble those of living birds, but Archaeopteryx was rather different from any bird we know of today: it had jaws lined with sharp teeth, three fingers ending in curving claws, and a long bony tail.

Archaeopteryx is a powerful piece of evidence that birds evolved from dinosaurs. The skeleton is most similar to the dinosaurs of the families Dromaeosauridae and Troodontidae. However, it is not believed to be a direct ancestor of modern birds, instead an off-shoot which eventually became extinct without spawning any further species. Reports of an apparently earlier bird, Protoavis, are considered to be unproven by most paleontologists.

Archaeopteryx - Fly or hop?

There is some controversy about whether Archaeopteryx could genuinely fly, or only hop around and glide from trees. The lack of a large breastbone suggests it was not a strong flier, but flight muscles might have attached to the bird's thick, boomerang-shaped wishbone, a birdlike feature. The large wings and long tail, however, suggest that it was both stable and maneuverable in the air. The shape of the wings is similar to birds which fly through trees and brush.

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). So far, Archaeopteryx has perhaps produced as many questions as answers, and the latest findings on this fossil are unlikely to be the last word.

The "Thermopolis" specimen, recently donated to the Wyoming Dinosaur Center in Thermopolis, Wyoming and described in the December 2, 2005 Science journal article "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." [2]

Archaeopteryx - Taxonomy

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 Eichstatt 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 specimens belong to the same species (New Scientist, 17 April 2004, p.17). However, significant differences exist between the specimens. In particular, the Munich and Eichstatt specimens differ from the London, Berlin, and Solnhofen specimens in being smaller, having different finger proportions, and in having more slender snouts lined with sharp 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.

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, but whether it actually is a feather of this species or another, yet undiscovered, proto-bird is unknown.
2. London Specimen (BMNH 37001, the holotype): Discovered in 1861 near Langenaltheim, Germany, and described in 1863 by Richard Owen, who made it the type specimen for the genus and species. Currently located at the British Museum of Natural History in London. It is missing its head.
3. Berlin Specimen (HMN 1880): Discovered in 1876 or 1877 near Blumenberg, Germany, and 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. 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. Munich Specimen (S6, formerly known as the Solnhofen-Aktien-Verein Specimen): Discovered in 1991 near Langenaltheim and described in 1993 by Wellnhofer. Currently located located at the Paläontologische Museum München in Munich. Only specimen with a breastbone (sternum). May be a new species, A. bavarica.
8. 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.
9. Thermopolis Specimen Discovered in Germany. Long in a private collection, described in 2005 by Mayr, Pohl, and Peters. Currently located at the Wyoming Dinosaur Center in Thermopolis, Wyoming. Has the best-preserved head and feet.

See also

• Feathered dinosaurs

Adapted from the Wikipedia article "Archaeopteryx", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki