Debate Continues Over Origin of Birds
The feathers are flying over a recent report in Science. A team of scientists led by John Ruben of Oregon State University reported their observations on the fossil remains of Longisquama insignis a small reptile that lived in Central Asia some 220 million years ago. Discovered in the late 1960's by Alexander Sharov, the lone Longisquama specimen was banished to a drawer in a Moscow institution. In the 1990's, it came to the attention of American scientists when it became part of a traveling Russian dinosaur exhibit.
Ruben and his colleagues noted six to eight pair of appendages, which resembled feathers; there was a central vane with a hollow shaft reminiscent of feathers on modern birds.
These findings were not convincing to some scientists. The prevailing theory is that birds evolved from the theropod dinosaur Archaeopteryx. The 145 million-year old fossils of Archaeopteryx shared many anatomical features with birds. Critics of the current report think there is little evidence that the appendages on Longisquama are feathers and find no other structures that link this non-theropod reptile to the branch of dinosaurs that are likely to have given rise to birds.
Ruben feels that they have good evidence and, off the record, suggests that Longisquama is an ideal bird ancestor. The authors hypothesize that "the combination of shared, specialized morphological characters of avian feathers and the pinnate integumentary appendages of Longisquama were unlikely to have evolved more than once." Longisquama pre-dates Archaeopteryx by 75 million years and may provide new insight into the evolution of modern birds.
(References: Science, June 2000, p 2124 and p 2202. )
Submitted by Pauline Garber