When a 150-million-year-old fossil having traits of both reptiles and birds was discovered in Bavaria, it was named Archaeopteryx lithographica. The discovery provided evidence that birds had descended from reptiles and thus lent support to Charles Darwin’s recently published theory of evolution by natural selection. Archaeopteryx lithographica has continued to be important in scientific debates regarding the evolutionary origin of birds.
In 1861,
Solnhofen limestone was mined extensively, because it made excellent lithographic plates. In the process of excavating this stone, miners unearthed a treasure trove of Jurassic fossils. The conditions for fossilization in the area had been ideal: Central Europe in the late Jurassic period was arid and tropical. Much of it was covered by a warm, shallow sea. A sparse vegetation of cycads, small conifers, ginkgos, and seed ferns grew on small islands in isolated coral lagoons. The water near the bottom of the lagoons was highly saline because of high evaporation rates, and it was low in oxygen because of plankton blooms. Thus, there were few scavengers or bacteria to consume the creatures that perished and fell to the seafloor. In addition, there were no currents to tear the dead animals apart.
The creatures that became buried underwent gentle fossilization in the soft, lime-rich muds that had accumulated from the fine-grained sediments that washed into these calm waters. Over the millennia, the mounting weight of the sediments compressed the mud into limestone. The fine grain of the muds preserved the microstructures of many creatures in unusual anatomical detail.
In 1861, the Solnhofen feather impression was brought to the attention of paleontologist Hermann von Meyer of Munich. This single fossil feather constituted the first evidence that birds had lived in the Jurassic period. Later that same year, rock cutters in the Solnhofen limestone quarry found the flattened skeleton of a small reptilian animal bearing wings and feathers. A quarryman gave the specimen to Karl Haberlein, a local doctor and amateur collector, to settle a medical bill. Like the feather, this skeleton, which was nearly complete except for part of its head, came to the attention of von Meyer, who announced its discovery and named the extinct creature Archaeopteryx lithographica.
In Greek, the genus name Archaeopteryx means “ancient wing,” and the species name lithographica refers to the use of the limestone matrix in lithography. The only way von Meyer knew that Archaeopteryx lithographica had had feathers was that these structures were exceptionally well preserved in the Solnhofen limestone. If no feathers had been discernible, the creature would have been classified as a reptile. Ironically, four years earlier, von Meyer had misidentified another Archaeopteryx lithographica fossil, a specimen of poor quality with no readily discernible feathers, as a pterodactyl, a reptile that had developed flight in a manner different from birds. That specimen, which had been unearthed in 1855, would not be correctly identified until 1970.
Archaeopteryx lithographica had many reptilian characteristics, including a blunt snout rather than a beak and small, sharp, reptilian teeth (modern birds are toothless). Archaeopteryx lithographica also had scaly skin and a flat sternum (breastbone), as do reptiles, and a long, bony, reptilian tail. In modern birds, by contrast, the breastbone has a keel for the attachment of flight muscles, and the vertebrae are reduced in number and partially fused. On three digits of its forelimbs, or wings, Archaeopteryx lithographica had reptilian claws, which it may have used for grasping prey.
Archaeopteryx lithographica also had a number of characteristics of modern birds. Its feathers were indistinguishable from modern feathers. The flight feathers of its wings were arranged in a manner similar to those of modern, flying birds. Archaeopteryx lithographica also had feathers in its tail, as do modern birds. These tail feathers were arranged in pairs along the sides of fifteen of its tail vertebrae. Although its skeletal structures related to flight were less well developed than in modern birds, Achaeopteryx lithographica did have a large furcula (wishbone), a structure composed of fused clavicles, or collarbones, which serves as a brace during birds’ up-and-down wing strokes. Archaeopteryx lithographica was probably capable of gliding and weak, flapping flight but not long, sustained flight.
The discovery of this intermediate creature between two major vertebrate taxonomic groups—reptiles and birds—provided timely evidence in support of the arguments Charles Darwin had recently advanced in his theory of evolution by natural selection. Archaeopteryx lithographica exemplified the transitional creatures Darwin had predicted, and it quickly became a focus of the debate over his theory. Two prominent figures who clashed in that controversy were paleontologist Thomas Henry Huxley, who was Darwin’s most eloquent champion, and Richard Owen
In 1862, Owen was instrumental in purchasing the fossilized skeleton from Haberlein to add to the museum’s
As of the early twenty-first century, six more skeletal fossils of Archaeopteryx lithographica had been discovered in limestones of the Solnhofen region. They ranged from the size of a blue jay to that of a large chicken. The two most famous specimens are the 1861 original, known as the “London specimen,” and a second skeleton, found in a quarry near Eichstatt in 1877. This 1877 skeleton, which was exquisitely preserved and the most complete of all the skeletons, is now in a museum in Berlin and is known as the “Berlin specimen.”
The discovery of Archaeopteryx lithographica not only provided evidence in general of the descent of birds from reptiles, thus bolstering Darwin’s theory of evolution, but also initiated a flurry of theorizing about the specific evolutionary origins of birds. As of the early twenty-first century, the fossils of Archaeopteryx lithographica were still the oldest fossils ever discovered that had feathers of a truly modern structure, and Archaeopteryx lithographica was widely accepted as the oldest known bird. It is not considered to be the first bird, however, nor is it the likely ancestor of modern birds. Most paleontologists place it on an evolutionary side branch.
Huxley’s view that birds arose from dinosaurs was unpopular until the 1970’s, when research revealed similarities between a newly discovered theropod dinosaur and Archaeopteryx lithographica. Most paleontologists now accept that birds arose from small, bipedal, predatory theropods during the Jurassic period, and many agree with Huxley that birds are actually dinosaurs. Some paleontologists maintain, however, that birds arose earlier, from an old and poorly defined reptilian stock called thecodonts, rather than from dinosaurs.
Archaeopteryx lithographica has also played a role in debate over the origins of avian flight. Some scientists suggest that the ancestors of Archaeopteryx lithographica lived in trees and initially glided before developing flapping flight. Others argue that the claws of Archaeopteryx lithographica were not suited to climbing and suggest that the creature’s ancestors at first ran along the ground with their forelimbs outstretched, then leapt from the ground, and eventually developed flight ability.
During the late twentieth century, fossils of feathered theropod dinosaurs were discovered in China. These creatures, which seem to be younger than Archaeopteryx lithographica, have fueled the controversy over avian origins. Views are likely to be refined as additional fossils are found.
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Barthel, Karl Werner, N. H. M. Swinburne, and S. Conway Morris. Solnhofen: A Study in Mesozoic Paleontology. Cambridge, England: Cambridge University Press, 1990. An updated translation of K. Werner Barthel’s 1978 work, Solnhofen: Ein Blick in Die Erdgeschichte. Illustrates many Solnhofen fossils, including those of Archaeopteryx lithographica; describes Solnhofen’s geology, palaeoecology, and fossil taxonomy. -
Chiappe, Luis M., and Lawrence M. Witmer. Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press, 2002. Examines the avian fossil record, including the many Mesozoic species discovered during the 1990’s, and discusses bird origins. -
Currie, Philip J., Eva B. Koppelhus, Martin A. Shugar, and Joanna L. Wright. Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. Bloomington: Indiana University Press, 2004. Presents evidence of close ties between dinosaurs and birds, and specifies the most likely processes by which the one evolved into the other. -
Gill, Frank B. Ornithology. 2d ed. New York: W. H. Freeman, 1995. Comprehensive college textbook on birds. The second chapter is devoted to Archaeopteryx lithographica and its relationship to bird origins. -
Paul, Gregory S. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press, 2002. Discusses the origins of the ability to fly in dinosaurs and in birds. Includes evidence that modern birds evolved from theropod dinosaurs. -
Shipman, Pat. Taking Wing: Archaeopteryx and the Evolution of Bird Flight. New York: Simon & Schuster, 1998. Recounts the discovery of the Archaeopteryx lithographica specimens and the role of Archaeopteryx lithographica in the controversy over evolution; discusses the evolution of birds, feathers, and flight.
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