[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: vaulting pterosaur launch, questions




David Marjanovic wrote:


>> Even the brooding hypothesis (which I like) doesn't explain why the
>> feathers of _Archaeopteryx_ were asymmetrical,
>
> It does, or at least it claims to do: the leading edge is more likely to
> contact the ground.


Hmm... do you really 'buy' that explanation?


> It also explains very nicely why tertials aren't remiges (not even in
> soaring birds with endless humeri) and why Archie lacks them altogether.


Not necessarily - especially if the emphasis is on maneuverability during the 
descent.  Sure, mammalian gliders and many reptilian ones (like _Draco_ and 
kuehneosaurs) have a continuous lift surface that connects the body wall to the 
limbs.  But the distal gliding surfaces (webbed feet) of "flying" frogs 
(_Rhacophorus_, etc) and "flying" lizards (_Ptychozoon_) accord a great deal of 
benefit in gliding.  True, in _Ptychozoon_ the cutaneous flaps play a role too; 
but those big webbed feet improve both the lift:drag ratio and maneuverability. 
 


> That doesn't mean we can't do science on this question. Had Archie been a
> glider, it would almost certainly have had tertials...


This is what the "Pouncing Proavis" hypothesis states.  However, the lack of 
tertials in _Archaeopteryx_ does not necessarily mean it didn't glide, nor that 
its ancestors didn't either.


>> nor why the tail was lined with rectrices.
>
> Indeed not, but for this you can always blame sexual selection :o)


Oh, you mean "display".  When there's no other explanation, then it must be 
display!  :-)


Refs.

Garner, J.P., Taylor, G.K., and Thomas, A.L.R. (1999).  On the origins of 
birds: The sequence of character acquisition in the evolution of avian flight.  
Proc. Biol. Sci. 266: 1259-1266. 

Young, B.A., Lee, C.A., and Daley, K.M. (2002).  On a flap and a foot: Aerial 
locomotion in the "flying" gecko, _Ptychozoon kuhli_.  J. Herpetology 36: 
412-418.




Cheers

Tim
_________________________________________________________________
Enjoy 5 GB of free, password-protected online storage.
http://www.windowslive.com/skydrive/overview.html?ocid=TXT_TAGLM_WL_Refresh_skydrive_062008