Re: Pterosaurs and birds, was Re: birds and pterosaurs

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "Michael Habib" <mhabib5@jhmi.edu>
To: "Jorge Dichenberg" <jorgedich@yahoo.com>
Cc: <dinosaur@usc.edu>
Sent: Monday, October 10, 2005 12:32 PM
Subject: Re: Pterosaurs and birds, was Re: birds and pterosaurs


> Oh, gotcha, I misunderstood before.  Interesting thought.  I wonder how 
> much of a large bird's metabolic costs go to feather replacement; that 
> would definitely be very interesting to know.  Thanks for clarifying that 
> point; I like it.

This also seems to be one of the reasons (perhaps the primary reason) that 
birds switched from symmetric to asymmetric flight feathers.  Symmetric 
flight feathers work fine aerodynamically, but the shafts have to be a lot 
heavier to provide the additional stiffness required to prevent flutter, so 
with that plus the redundant area on one side, the symmetric feathers would 
be a lot heavier and therefore more costly to replace during the moult.

> Very large birds were probably quite efficient, but large pterosaurs were 
> probably more efficient as soarers, with regards to energy extraction 
> (though soaring birds may have other advantages we are missing).

Pterosaurs appear to have more efficient wings, and relatively smaller 
bodies, but those advantages are probably swallowed up by their larger, 
draggier heads and necks.  All up efficiency for a fully derived soaring 
bird and a fully derived pterosaur are probably quite similar (nature tends 
toward minimalism, with animals on the whole doing no better than required 
for a given energy input).  For example, if pterosaurs get too good at 
flying, they'll likely start putting more effort into sexual or species 
recognition display structures and other things that degrade their overall 
flight performance back to about what the energy extracted from the 
atmosphere and their food supply can support.

> But it may just be because the growth is being measured as a linear growth 
> rate, and the feather has to scale as 3-D structure (albeit a flat one).

It's still 3-D.  Mass goes up a lot with increased length, even when not 
precisely following the square-cube rule.