Re: A New Hypothesis for the Origin of Flight?

["David Marjanovic" <david.marjanovic@gmx.at>]

>  When small dinosaurs took to the trees, they
> developed small stiff pin-like feathers on their
> forearms, possibly for adding grip to the hand, or
> using them like the spines on a mantis arm to catch
> insects with.

Interesting idea, but I think the claws serve this function already, and
better. Try HOBHY for explaining why wings evolved :-)

> When they moved among branches, they
> didn't leap or glide, [...] The retroverted or reduced
> pubes and more pneumatic thoracic cavity in some forms
> may be an attempt to push the center of gravity
> backward, so the legs could fully extend the body
> forward, and still remain balanced on the perch.

Sounds good.

> As they reached continually further, they might flail
> their arms, trying to grasp a branch or twig just out
> of reach....a precursor to flapping.

Basically the same as what has recently been proposed for bats. Very good
IMHO, because that way you get trees-down without parachuting and gliding.

> Even if they did manage
> to get a good grip, powerful muscles would be needed
> to pull the body onto the next branch....a precursor
> to the avian flight musculature.

Possible. But very flexible arms and hands would be very advantageous here.
I don't see them in any described dinosaur (will be interesting to read what
the aye-aye dino has... no, that's not a prediction, I don't know it :-) )

> A reversed hallux would be
> advantageous, because uni-directional toes
> can't maintain a good grip if you're metatarsus
> is almost in the same vertical plane
> as the branch you're on.

And still, it isn't reverted except in and very close to Pygostylia. Even
that of *Microraptor* doesn't originate at the same level as the other toes,
is pretty short for a bird, and is probably not (fully) reverted.

> An arctometatarsalian or co-ossified pes would
> also be pretty handy in this situation.

Like that of *Rahonavis* :->

> In secondarily terrestrial Oviraptorosaurs,
> the pygostyle would be lost, and genetic duplication
> of a proximal caudal "design" would re-lengthen the
> tail, effectively masking what was left of the
> Dromaeosaur-style tail. The pubes would swing forward,
> and feathers would atrophy to more manageable sizes.

Sounds very good to me. Just in that case I'd expect at least basal
oviraptorosaurs to have hen-like feet (with a reverted hallux). (Of
course... if *Eshanosaurus* is indeed a segnosaur, then oviraptorosaurs are
at least as old as that and had _plenty_ of time to reduce their halluces.)

> Hopefully
> this is a convincing (and testable) example of how
> flapping could arise, and exactly what the newest
> Jehol theropods were doing with their unusually long
> tails and arms. So, let's try to tear it apart.

It's certainly testable, as it makes testable predictions. See above for
some of my attempts at tests. On the whole I'd expect a lot more climbing
adaptations in those theropods, including basal birds.