Monday, August 27, 2012

Taking Wing: Archaeopteryx and the Evolution of Bird Flight

Archaeopteryx is known as the first bird, and its fossils are strikingly beautiful. They are also still extremely controversial, even 150 years after their discovery in Germany. Taking Wing: Archaeopteryx and the Evolution of Bird Flight by Pat Shipman starts by tracing the history of each specimen found in the Solnhofen limestone region of Bavaria. The bulk of the book however is devoted to the scientific data gleaned from these fossils over the past century and a half, and Shipman's analysis of all the theories, both established and well as controversial, in regards to avian evolution and the birth of flight.

Taking Wing is comprised of punny chapter titles wherein well-known avian phrases are used to discuss certain topics. For example. the chapter entitled "Birds of a Feather" thus deals with the development of feathers in bird evolution; "A Bird in the Hand" relates the evolution of wings as extensions of the five-finger extremities; "One Fell Swoop" shares one specific theory where birds may have acquired flight from a "trees down" or arboreal hypothesis (versus a "ground up" or cursorial hypothesis). Scientists are divided how birds developed flight: were they tree-dwellers that glided, or swooped to the ground, later to develop full flapping flight, or did the ancestors of birds live on the ground, and developed flight after a run-and-jump takeoff? This debate was argued at a 1984 international Archaeopteryx conference in Eichstätt, Germany (home to a fossil discovery in 1951). The conference closed with the following statement, which did not please everyone and is still argued today:

"Archaeopteryx was an active, cursorial predator and was also facultatively arboreal; it was a glider and a feebly powered, or flapping flier. Finally, it was incapable of takeoff and flight from the ground upward..."

Shipman spent exhaustive care explaining bird anatomy, avian musculature and bone structure yet at times it felt that she was speaking to fellow ornithologists and not to armchair fossil fans like myself. I did like that Shipman addressed the reader and asked questions on our behalf, so she knew whom she was writing for. She also linked the chapters together by asking a question at the end of one and then endeavouring to answer it at the beginning of another, so the book flowed well and made the story of bird evolution come alive.

Some scientists do not even believe that Archaeopteryx could fly. It was profoundly interesting to read their theories for the origins of wings and feathers, since if wings and feathers preceded flight, then they had to have another primal purpose. As I read Shipman's analyses of all these theories, I came to the conclusion that Archaeopteryx could very possibly not be a fully developed and flying bird as we know today, but rather a creature caught in the middle of reptilian to avian evolution. At the end of Taking Wing, Shipman writes:

"The key to understanding Archaeopteryx is recognizing that it was not a bird as birds are today, but an evolutionary fledgling. We should not have expected otherwise. I do not fool myself, however, that the debates are over or that the arboreal proponents will suddenly abandon their position."

At any time the fossil record can yield new light on questionable theories or refute the claims of others. The discovery of feathered dinosaurs has cast doubt on some theories and strengthened the "ground up" or cursorial hypothesis. Shipman offers care and caution in future avian analysis:

"The fossil record of avian evolution is a tangled wing. Disentangle it properly and you can suddenly fly and soar to new heights, gaining new perspectives and understandings. Leave it tangled and your attempts at flight are bound to end in disastrous crashes."

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