Friday, October 2, 2009

More on Anchiornis

A couple days ago I mentioned the new Jurassic feathered dinosaur published online by Nature last week. Well, this week's issue of Nature has the full scoop on Anchiornis huxleyi. Witmer has a commentary, and Hu et al. provide the formal description. Witmer summarizes the problem of finding feathered dinosaurs later in fossil "time" than the much more avian Archaeopteryx:
It has been argued that this 'temporal paradox' (how can a 'descendant' arise before an 'ancestor'?) both invalidates the theropod ancestry of birds and, reversing the ancestor-descendant relationship, suggests that some of the Cretaceous bird-like theropods actually descended from Jurassic Archaeopteryx-like birds.
(Those would be the hypotheses of Feduccia.) With this new fossil, that "temporal paradox" is resolved: Anchiornis is found stratigraphically lower than Archaeopteryx.

What's more interesting is that Anchiornis is another four-winged dinosaur, like the other feathered dinosaurs Microraptor and Pedopenna. All of these species had forelimbs and hindlimbs with long feathers (like wings). Whether they were actual wings by which the animals could fly is unknown, but they certainly look like flight or gliding structures. So the new idea for the evolution of flight is that the earliest bird ancestors evolved four wings first, then two of those wings reverted to legs while or before modern birds evolved.

Weird, but cool. Four-winged bird things!

Hu et al. 2009. A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus. Nature 461:640-643.

Witmer. 2009. Feathered dinosaurs in a tangle. Nature 461:601-602.