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Re: Feather Flap

Scott Hartman wrote:

See, this is what I'm calling special pleading: we don't even know if it's possible for arboreal gliding to evolve in linneages that aren't already specialized for arboreal locomotion,

We don't yet know that this is *not* possible.

yet because we "know" that trees were involved in bird evolution you are willing to jump right into arguements for how maniraptorans "could have" done it.

This is not what I was saying at all. I was not claiming that trees were involved in bird evolution. What I was saying is that in certain maniraptorans there were changes in the morphology of the pes. OK, these changes weren't particularly striking, and they mostly center on the proportions of the digits and the shape of the claws. My question is: why these changes? Is it pure coincidence that these characters first appear around the same place in the theropod tree as the first aerodynamic feathers?

If you want an example of "special pleading", you only have to look at the argument that _Archaeopteryx_ had a specialized perching pes because it "must have" lived in trees. The BANDits are guilty of this one.

Surely in the absence of specialized arborreal linneages of non-avian theropods the burden of proof must be on those who think that arboreal gliding played a role in early bird evolution, yet not only is there not overwhelming evidence of arborreal adaptations, the case is remarkably weak and continues to get a free pass by many in the field.

The skeleton (manus and pes included) may not be specialized for arboreality, but the integument of microraptorans and _Archaeopteryx_ is certainly specialized for aerial locomotion.

Don't get me wrong, I agree that it's easier to explain bird flight if wee invoke trees, but evolution isn't necessarily arranged for our convenience.

Definitely. I don't have much time for the argument that avian flight must have evolved "trees down" because it is "easier" to evolve flight this way. The "BANDits" are guilty of this one too. In my book, as long as a "ground-up" origin is physically possible, it's a viable hypothesis that has yet to be refuted.

Personally, I favor a scenario for the origin of avian flight in which both cursoriality/terrestriality and scansoriality/arboreality each played a role. The ol' "trees-down" vs "ground-up" dichotomy just doesn't work for me.

The data to support such a scenario is so far weak, and the only way to get around it is for more people to study the problem, not to pretend like there isn't one.

I understand that. I agree that the hypothesis of arboreal locomotion in theropods needs more rigor, and I applaud your efforts to play Devil's Advocate.

Absolutely, which is why there is a slide of them in the presentaion I give to the public. However in both groups the main lift-generating surface is still confluent with the stomach (in the case of gliding frogs, the flattened ventral stomach surface has at least as much area to create lift as the webbing between the toes ).

Are you certain that "flying frogs" use their bodies as lift-generating surfaces?

The smaller distal membranes are used for control...the exact mechanism I'm invoking for maniraptorans, except not for tree to tree locomotion,

This sounds a little like the "Pouncing Proavis" model of Garner et al. (1999)...

Garner, J.P., Taylor, G.K. & Thomas, A.L.R. (1999). On the origin of birds: the sequence of character acquisition in the evolution of avian flight. Proc. Roy. Soc. London B 266: 1259-1266

since clearly maniraptorans (including early birds...under any definiton) are not using their stomachs as a significant lift-inducing mechanism.

What about the tail?

Indeed, _some_ maniraptorans do show traits that _may_ be associated with arboreality. I'm really not saying that it isn't possible, just that the evidence is faaaaar worse than the common perception of bird origins would imply.

In some quarters, yes. I agree wholeheartedly. But I do think that vertebrate paleontologists have taken a much more measured approach to this issue than certain (but not all) non-paleontologists.



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