Re: Phylogeny of Maniraptora

["Tim Williams" <twilliams_alpha@hotmail.com>]

James R. Cunningham <jrccea@bellsouth.net> wrote:

> Doesn't this make a perhaps unwarranted presumption that passive gliding
> precedes active flight?

I said "one gradational pathway for the evolution of active flight"; I 
recognize that there are others.  Many, many others.  The hypothesis that 
passive gliding preceded active flight is one possible pathway.  "Flapping 
start" models represent another pathway.

> Why? Perhaps it used the forewings as stationary canards while flapping 
> with the hindwings?

Yep, I'm not discounting that possibility.  But again, using the hindlimbs 
for flapping implies a novel method of flight.  This model may be 
aerodynamically viable, but was it biomechanically possible?  And, as you 
note...

> I only point out that it can't be discounted without investigation, and 
> insofar as I know -- it hasn't been investigated yet.

I would add that I didn't say that four-winged flying was unlikely; just 
that the relatively short arms of _M. gui_, compared to _Archaeopteryx_ and 
other birds, and even to some other dromaeosaurids (including taxa that show 
no evidence of aerodynamic locomotion) undermines the assertion that its 
forelimbs were used as flapping wings in powered flight.  Still, I'm happy 
to be proved wrong.

> Perhaps large (non-vertebrate) dragonflies might be able to partially 
> address this issue.

As I'm sure you're aware, dragonflies are highly adept fliers.  I would add 
that multiple pairs of wings does appear to be the primitive condition for 
the first flying (pterygote) insects.  As arthropods, the first insects also 
had the luxury of multiple appendages; vertebrates have to make do with a 
maximum of four (five including the tail).

> Doesn't this presume that all pterosaurs incorporate the hindlimb into the 
> flight membrane?

Oh no.  I did say "may use".  I'm aware that at least some pterosaurs had 
the flight surface supported only by the forelimbs.

>  Note that I personally think there were enough pterosaur niches to be 
> filled and enough pterosaur species filling them that both conditions might 
> well arise, with the independent condition more likely where yaw authority 
> issues provided a need.

Agreed.



Tim

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