Wednesday, July 27, 2011

The Cultural Evolution of "Ancient Wing"

My first "serious" fascination with dinosaurs began in the spring of 1993 when I came home from school to find the April 26th issue of Time magazine sitting on the dining room table among random envelopes and junk mail. The cover showed a group of Mononychus (Mononychi?) and the bold title "The Truth About Dinosaurs", followed by the somewhat philosophical subtitle, "Surprise: Just about everything you believe is wrong". That subtitle keeps coming back to me, time and again.

An article published today in Nature by Xu et al. reports on a new Archaeopteryx-like theropod from China named Xiaotingia zhengi that possesses a number of characteristics that have traditionally been regarded as diagnostic for Avialae, the clade of dinosaurs including birds and their closest extinct relatives such as Archaeopteryx. Phylogenetic analysis of X. zhengi suggests that it is an archaeopterygids, the clade that includes Archaeopteryx, but more importantly, it moves archaeopterygids from within the Avialae clade to the sister group Deinonychosauria, the clade including "raptors" such as Dromaeosauroids and Troodonoids!

For more information, I recommend reading Larry Witmer's excellent News & Views companion piece located here, where he discusses the significance much better than I can.

The historical significance of Archaeopteryx is also an interesting aspect of this story. First described by Meyer in 1861 (yes, 150 years ago), Archaeopteryx became a poster child for evolution very early on; the description came only 2 years after Darwin published "On the Origin of Species". Since then, about 10 specimens have been found, all from Bavaria's Jurassic Solnhofen limestone, a world famous lagerstaaten locality. Of these specimens, the dubbed "Berlin specimen" is arguably one of the most iconic images in paleontology.

Throughout the years, Archaeopteryx lithographica has been a staple of imagery to convey the concepts of evolution. I have used images and casts of this animal on more occasions that I can remember to exemplify the evolutionary transitions from non-avian dinosaurs to extant birds. Archaeopteryx has always been the steady base for such investigations as "the first bird".

That has now changed.

But for how long? This is only one specimen that de-perches Archaeopteryx from its 150-year-old comfy tree-branch. When Xu et al. removed X. zhengi from their analysis, Archaeopteryx went right back to Avialae. Clearly, this is an extremely important milestone in avian evolution, but one that will surely ruffle many feathers by the time it gets settled out, if ever.

Happy Birthday, Archaeopteryx. At 150 years old you never cease to to create a controversy, whether "promoting the dangerous doctrine of Darwinism" or continuing to make science fun and challenging.