ARCHAEOPTERYX

Archaeopteryx skeleton, cast made from a fossil found in limestone matrix. the oldest known fossil animal that is generally accepted as a bird. It flourished during the Late Jurassic Period (the Late Jurassic occurred from 163 to 144 million years ago). The known fossil specimens were found in the Solenhofen Limestone Formation in Bavaria, a very fine-grained Jurassic limestone formed in a shallow, tropical marine environment, probably in a coral lagoon, where lime-rich muds slowly accumulated and permitted fossil material to be exceptionally well preserved. Several of the fossil skeletons have clear impressions of feathers. The sizes of the specimens range from that of a blue jay to that of a large chicken. Archaeopteryx shared many anatomical characters with theropods (q.v.; small bipedal dinosaurs). The skull, like those of birds, possessed an expanded braincase, large eye sockets, and a pronounced beak. Unlike modern birds, however, Archaeopteryx had well-developed teeth. The head was balanced upon a long, thin, and probably very flexible neck. The spinal column was simple in character. A long, well-developed tail was present, similar in structure to that of the smaller dinosaurs, but it had feathers in a row on either side. The hind legs possessed three claws at their extremities and were birdlike. Archaeopteryx had well-developed wings, and the structure and arrangement of its wing featherssimilar to what is found in modern birdsindicate that it could fly. Skeletal structures related to flight are incompletely developed, however, suggesting that Archaeopteryx may have been an awkward flier. Although Archaeopteryx is almost universally accepted as a bird, some experts consider it to have been a feathered dinosaur because of its theropod-like skeletal anatomy.