Friday, September 21, 2007

Greg Paul Was Right...AGAIN!

I mean, Predatory Dinosaurs of the World was published in 1988, and back then, Greg Paul was illustrating his raptor dinosaurs with feathers. Extensive feathers. This is just another instance of the man knowing the Theropoda better than most professional paleontologists. Just for fun, here are some more Greg Paul theories put forth in Predatory Dinosaurs that were later proven absolutely freaking correct:
1) Spinosaurus and Baryonyx form a monophyletic clade.
2) Spinosaurus is not a big allosaur, and was not related to Acrocanthosaurus.
3) Archaeopteryx has a hyperextendable second toe.
4) Birds, dromaeosaurs, and troodontids form a monophyletic clade (now known as Paraves).
5) Carnotaurus is a big ceratosaur.
6) Ceratosaurus and Coelophysis shared a recent common ancestor.
7) Some higher theropods were arboreal.
8) Many theropods, including dromaeosaurs, troodontids, and higher tetanurines had feathers.

And, just to balance things out, here are a few things he was wrong about. In 1988.

1) Tyrannosaurs evolved from allosaurs (he still alludes to this in 2003's Dinosaurs of the Air)
2) Deinonychus and Velociraptor are cogeneric.
3) Therizinosaurs were incredibly derived, late-surviving prosauropods.

Pretty good balance in favor of "this guy is right a lot." Anyway, I bring this up because in today's issue of Science, Turner, Makovicky & Norell announced that Velociraptor mongolensis, which is actually one of the smallest core group dromaeosaurs, had feathers. They came to this conclusion after studying a single well-preserved ulnar bone, which retains feather quill knobs. In modern birds, quill knobs line the ulnar bones and serve to attach the large secondary feathers and greater secondary coverts to the ulna itself with the help of follicular ligaments. That is, the quills don't erupt from the bone, but the secondary feather follicles are very deep, ensuring their rigidity. This is actually nothing compared to primary feathers, which grow from the crest of the 2nd finger over the 3rd finger. The entire primary quill is covered by a thick web of skin. You can't pull a bird's primaries off without damaging the manual bones.

Anyway, that's not the point. The authors suppose that, given the amount of quill knobs preserved (6) and the spacing of individual knobs, Velociraptor probably had 14 secondary feathers. Archaeopteryx has around 12, and Microraptor may have had 18. This may seem like a large range in feather count, but feather growth is not set in stone like, say, number of cervical vertebrae (which isn't either, see what I mean). Even within a single species of living bird, there is variation in the number of secondary feathers.

The authors close the short paper by noting that: "An examination of the living families of birds shows a significant correlation between the absence of ulnar papillae and the loss and/or reduction in volancy, even though some strong flyers lack papillae. This raises the possibility that ulnar papillar reduction or absence in large-bodied derived dromaeosaurids reflects loss of aerodynamic capabilities from the clade's ancestral members." What this basically means is that, in extent birds, the reduction and loss of quill knobs is often correlated with a reduced flight performance. The fact that Velociraptor still has quill knobs (and a lot of them) suggests that its immediate ancestors could fly to some degree, although Velociraptor itself was clearly flightless.
So, actually, that means Greg Paul is right about one more thing, from his more recent Dinosaurs of the Air: Deinonychosaurs are secondarily flightless. And thus, we may be able to replace the "Paraves" label with "Aves" and call it good. We can think of Velociraptor, Troodon, and all the little deinonychosaurs in between as the first flightless birds!


Will Baird said...

Aren't we jumping the gun that the manniraptors are flightless birds here?

PDC that they have such solid evidence. I am still awaiting Feduccia counterbarrage.

Zach Miller said...

Not maniraptors in general. It's pretty clear that therizinosaurs aren't that close to birds, and may instead form an outgroup to the maniraptors, along with their more birdy cousins, the oviraptors. But oviraptors are clearly more avian than therizinosaurs (although the two groups share similar dentition--it's confusing). Anyway, oviraptors likely developed their avian features by way of paralellism (mispelled?).

The point is, Paraves is a specific fixture of Maniraptora which includes (traditionally) birds and deinonychosaurs (raptors + troodontids). However, since primitive deinonychosaurs seem to have been flighted to some degree, and have just as many adaptation to the sky as the urvogal (if not more in some genera), it might be time to reconsider what defines a bird.

And yes, it's all arbitrary definitional stuff. It's just that if Archaeopteryx is the baseline, then deinonychosaurs clearly pass the "bird" test. I think that their traditional non-avian definition is holding a lot of workers back.

Julia said...

Oh Phylocode will have a field day with that! Didn't know that about primary feathers. Will look at my TGI Fridays Jack Daniels wings in a new light...