Archaeopteryx: The Transitional Fossil
Paleontologists view Archaeopteryx as a transition between dinosaurs and modern birds. With its blend of avian and reptilian features, it was thought by many to have been the earliest bird. Discovered in 1860 in Germany, it is sometimes referred to as Urvogel, the German word for "original bird" or "first bird." Recent discoveries, however, have made scientists rethink that status.
The more common name Archaeopteryx is a combination of two ancient Greek words: archaīos, meaning "ancient," and ptéryx, meaning "feather" or "wing." All 11 fossil specimens have been assigned, with some controversy, to a single species, Archaeopteryx lithographica.
Archaeopteryx lived around 151 million to 149 million years ago — during the Tithonian period, the late stage of the Jurassic era — in what is now southern Germany. At the time Europe was an archipelago and was much closer to the equator than it is today, providing this bird-like dinosaur with a fairly warm home close to the sea in which it could thrive.
Is it a bird or a dinosaur?
Despite having feathers, broad wings and a presumed ability to fly or glide — even if limited — Archaeopteryx had more in common with dinosaurs than with birds. Like deinonychosaurs, it had jaws with sharp teeth, three fingers with claws, a long bony tail and hyperextensible second toes known as "killing claws." It also had features in common with theropods, including a nearly identical hind leg bone structure that was clearly visible.
Archaeopteryx was about the size of a raven or crow and its tail was unusually long in comparison to its body length. It could reach up to 20 inches (50 centimeters) in body length, weighing 1.8 lbs. to 2.2 lbs. (0.8 kilogram to 1 kilogram).
Specimens of Archaeopteryx were most notable for their well-developed asymmetrical flight feathers. The tail feathers were not as asymmetrical and had firm vanes, also similar to today's birds. The thumb, however, did not yet have a separately movable tuft of stiff feathers as seen in modern avians.
The down-like feathers of Archaeopteryx more closely resembled the fluffy down found on the Sinosauropteryx, a small, non-avian theropod, than that of a bird. In 2011, using scanning electron microscopy technology and energy-dispersive X-ray analysis, scientists determined that Archaeopteryx's feathers were black.
While there were feathers on its broad wings, which were rounded at the ends, no feathers or down have been found on Archaeopteryx's head or neck. Scientists continue to debate the reason for the lack of covering in these areas. Some paleontologists believe that this is due to the fact that the Archaeopteryx's head and upper neck were scaled more like a reptile's, while others believe that this is a result of decomposition. [Images: Dinosaurs That Learned to Fly]
Archaeopteryx had a flat breastbone and ribs along the stomach, which are two skeletal features that are found in reptiles. Its flat breastbone suggests that Archaeopteryx was not a very strong flier, but flight muscles might have been supported by its thick, boomerang-shaped wishbone or perhaps attached to its sternum. Its hollow bones and light weight lead scientists to believe it was able to get off the ground fairly easily, however.
Later specimens indicate Archaeopteryx lacked a perching foot — a completely reversed hind toe — so it was believed that Archaeopteryx did not spend time in trees. Scientists speculate that it behaved much like a peacock, spending much of its time on the ground and flying short distances when necessary to evade its numerous predators.
What did Archaeopteryx eat?
Archaeopteryx was a carnivore, feasting on lizards, frogs, beetles, dragonflies and mites. It would even use its long sharp bill and teeth to pick mites and other insects from its skin and eat them. It would also catch insects on the ground or in trees, and scientists believe it possibly caught insects in the feathers of its wings.
While it did have "killing claws," those are believed to be evolutionary remnants rather than useful tools, as Archaeopteryx's diet of mostly insects and small animals didn't present a need to hunt or kill its prey.
The first discovery of Archaeopteryx was in 1860, when a solitary feather was found. Paleontologists cannot be certain that this feather is actually from Archaeopteryx or another species of prehistoric bird, but it remains on display at the Humboldt Museum fur Naturkunde in Berlin.
The next significant discovery came about a year later when an Archaeopteryx skeleton was located near Langenaltheim, Germany. The skeleton was given to a doctor as a form of payment and he later sold it to the London Natural History Museum. This specimen was missing most of its skull and neck vertebrae. The discovery coincided with the publication of Darwin's "On the Origin of Species," and the specimen seemed to confirm his theories. Archaeopteryx has since become central to the understanding of evolution.
Since the discovery of the first Archaeopteryx skeleton, 10 additional specimens have been unearthed. The most complete fossil is referred to as the Berlin Specimen and was discovered in 1876 near Eichstatt, Germany. This discovery was made by Jakob Niemeyer, but was eventually owned by Johann Dorr, who put the fossil up for auction in 1881. The fossil wound up being purchased by the Humboldt Museum fur Naturkunde, where it still resides.
The Berlin Specimen is the first specimen to be located with a head intact. Further specimens include the Maxberg Specimen, which was discovered in 1958 near Langenaltheim and includes the torso.
The Haarlem Specimen was excavated in 1855 near Riedenburg, Germany, by von Meyer. This fossil is composed of limb bones, cervical vertebrae and ribs. Although originally classified as a Pterodactylus, this specimen was later reclassified as an Archaeopteryx.
Dethroned as first bird
In 2011, scientists uncovered a fossil in China whose combination of features unexpectedly suggests Archaeopteryx was actually just a relative of the lineage that ultimately gave rise to birds. The new specimen, Xiaotingia zhengi, was found in Liaoning in China, where many other extraordinary specimens of feathered dinosaurs and early birds have been unearthed.
When the researchers analyzed features of Xiaotingia and Archaeopteryx, the resulting family tree clustered them together. Unexpectedly, it also yanked them out of the avialan category — dinosaurlike birds — and placed the duo with the deinonychosaurs — birdlike dinosaurs.
The analysis also suggested the earliest known avialan is currently a pigeon-size feathered creature known as Epidexipteryx hui recently discovered in Inner Mongolia, China.
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