Monday, September 28, 2009

Anchiornis


Anchiornis huxleyi, from the Nature paper.

A strong piece of evidence for the theropod origin of birds was announced last week, in an early online version of the current issue of Nature (click for original paper by Xu et al). From the fertile Jurassic strata of northeastern China comes Anchiornis huxleyi. This extravagantly feathered theropod of the troodontid family predates the earliest known bird, Archaeopteryx, and is a blow to the "temporal paradox" argument against the theropod origin.

There are three groups that make up the clade Paraves. The Troodontids, which include this new find; the Avialans, which include Archaeopteryx and later birds; and the Dromaeosaurids, which include those dinosaurs popularly regarded as the "raptors." Paleontologist Xing Xu and colleagues note that with this discovery, basal members of each of these groups have been found which feature a "four-winged" body plan. It appears that long feathers first evolved on the outer (distal, in anatomical terminology) end of the limbs, meaning that the scales we see on the feet of most modern birds was a later adaptation.

In all this further points to the idea that the first flying vertebrates evolved from an arboreal, gliding ancestor. I'm interested to see if a future study extends the climbing function recently attributed to Cretaceous dromaeosaur sickle claws to earlier, Jurassic maniraptors.

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