Archaeopteryx

Archaeopteryx is a dinosaur known from Jurassic fossils that remarkably exhibits feathers and other features once thought exclusive to birds. Specimens are regarded as among the most beautiful and significant ever found, as they document an important example of ancient life on the evolutionary path of [Page 47]flying birds arising from dinosaur ancestors. The first description of this “dinosaur-bird” in the 19th century famously helped ignite the evolution debate, and Archaeopteryx remains a relevant symbol of scientific enlightenment even today.

Adult Archaeopteryx was a crow-sized, bipedal, feathered dinosaur approximately 0.5 meters long. Although its exact evolutionary relationship has long been enigmatic, it is widely acknowledged to be a basal member of the Eumaniraptora, a branch of theropod dinosaurs that evolved in the Middle Jurassic and some of whose descendants would later give rise to modern birds, Aves.

Specimens of Archaeopteryx have been discovered mostly in the 150-million-year-old rocks of Solnhofen, Germany, where finely laminated limestone preserves an exceptionally rich and diverse record of fossilized ancient life. The prehistoric landscape that formed this momentous resource is thought to have been a low, shrub-covered archipelago. Lime-rich mud washed into and filled its shallow lagoons, burying and preserving the mortal remains of its surrounding inhabitants, including dinosaurs, mammals, reptiles, fish, plants, and insects. Thanks to the fine-grained nature of the sediment and other taphonomic factors, the fossils of the Solnhofen limestone are often exquisitely detailed. Even soft tissues are preserved, such as the feathers that marked the epochal discovery of Archaeopteryx (which means “ancient wing” or “flight”) in the 19th century.

Because of its being extensively covered with well-developed feathers, the Archaeopteryx has long been termed the world's most primitive bird. Indeed it seems to display many aspects common to modern birds and conducive to flight: arms with feathers to form broad wings, primary asymmetric “flight” feathers, small body size, hollow limb bones, relatively large brain with well-developed locomotor regions, and, the boomerang-shaped furcula (or “wishbone”) commonly found in modern birds.

Unlike modern birds, however, Archaeopteryx also had jaws with sharp teeth, clawed forelimbs that extended forward of the “wing,” and a long bony tail similar to other carnivorous dinosaurs at the time. Moreover, a plethora of recent discoveries of feathered dinosaurs with similar traits have been found, predominantiy in China, that indicate that Archaeopteryx has no unique characteristics shared with birds that cannot be found in dinosaurs.

Archaeopteryx is an early, bird-like, feathered dinosaur, dating from about 150 million years ago during the Jurassic period, when many dinosaurs lived. Current research on this fossil and others using hi-tech methods has greatly strengthened our ideas about the evolutionary tie between dinosaurs and birds. This Archaeopteryx example, coined the “Thermopolis”specimen, is one of the most recently described discoveries

Source: Courtesy of Wyoming Dinosaur Center/Scott Hartman.

The flight capability and habits of Archaeopteryx have long been controversial. The latest specimens show that the extent of primary feathers along the bones of the arms was more limited than first thought, thereby decreasing the area available for a flight surface if used as a wing. Additionally, the lack of certain structures in the shoulder girdle combine to rule out powered flight, although limited flapping and gliding may have been possible. The first toe, called a hallux, is not fully reversed so as to specialize in grasping onto branches as in arboreal dwelling birds. And the second toe had a hyperextensible claw, similar to dromaeosaurid theropod dinosaurs but not modern birds. Collectively these suggest that Archaeopteryx retained the predominantiy [Page 48]ground-dwelling habits of its forerunners and could not sustain powered flight.

...