Archaeopteryx
Archaeopteryx lithographica is the earliest and most primitive known bird. Since the first discovery of a single feather in 1860, only six specimens of Archaeopteryx have been found (if Wellnhoferia is a valid genus); all come from the Late Jurassic Solnhofen limestone of southern Germany. The first skeleton is now housed at the Natural History Museum, London, and the most spectacular is the famed Berlin Specimen at the Humboldt Museum, in Berlin.
Its name comes form the limestone where the first discovered fossil was printed. The limestone was found in Solnhofen, Germany. It was formed in the Jurassic, 150 million years ago, which gives a clue of when the archaeopteryx lived. 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 derived theropod dinosaur, and it is a powerful piece of evidence that birds evolved from reptiles, in particular, dinosaurs. The skeleton is most similar to the dinosaurs of the families Dromaeosauridae (Velociraptor, Deinonychus, Utahraptor and their relatives) and Troodontidae.
There is some controversy regarding the question of 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. 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.
Archaeopteryx continues to play an important part in scientific debates about the origin and evolution of birds. Some scientists see Archaeopteryxas 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). Other scientists see Archaeopteryxas running quickly along the ground, supporting the idea that birds evolved flight by running (the "ground up" hypothesis). 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.
A seventh skeleton, once described as an Archaeopteryx specimen, was proposed in 2001 to have belonged instead to a new species Wellnhoferia grandis - this has remained contentious; the six remaining skeletons are now all assigned to the species Archaeopteryx lithographica, eliminating the putative species A. recurva and A. siemensii (New Scientist, 17 April 2004, p. 17).