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Re: Flightless pterosaur indicators




--- On Wed, 3/24/10, David Peters <davidpeters@att.net> wrote:

> From: David Peters <davidpeters@att.net>
> Subject: re: Flightless pterosaur indicators
> To: "dinosaur mailing list" <dinosaur@usc.edu>
> Date: Wednesday, March 24, 2010, 7:39 PM
> Seems to me three indicators might
> have to include:
> 
> 1. Lack of predators in the environment

Can't prove a negative, especially in the fossil record, so this one, while 
valid, isn't especially helpful for actual identification purposes.

> 2. Any change in morphology that prevents flight
> including:
> a) reduction of wing length, 
> b) reduction of the pectoral girdle (and its anchoring
> muscles), 
> c) morphological changes that move the center of
> aerodynamic balance away from the wing root. 

I would add a lack of robustness in the forelimbs, but pterosaur bones are so 
thin and fragile anyway that it might be hard to recognize. :/

> 3. Death of the pterosaur    ;-) (had to throw
> that one in)

But by that standard all known pterosaurs are flightless. :P Unless you throw 
them, anyway! >:D

> If pterosaur wings originally developed as secondary sexual
> characteristics (after all they can be folded and deployed),
> then perhaps they were retained in flightless forms
> (analogous to the Kagu), for the same usage. 

I doubt they evolved as sexual displays, as fashionable as those types of 
suggestions are nowadays. It's just too easy and plausible to picture a flying 
squirrel-type membrane stretched from digit IV to the leg as the precursor to 
the pterosaur wing.

>So, if we're
> going to find flightless pterosaurs, I think our best bet is
> to look for the ones with smaller shoulders. What the
> threshold dimensions might be I leave to the engineers and
> mathematicians. If anyone wants to figure those equations
> out, please contact me off list and we'll have a project. 
> 
> Or do pterosaurs also need large shoulders to walk around
> quadrupedally?
> 
> David Peters
> davidpeters@att.net

That's what Augusto Haro argued earlier in the thread. I think he's on the 
right track. Birds can afford to lose the musculature while becoming 
flightless- the organs the muscles power are no longer used for locomotion. 
Pterosaurs, as quadrupeds, would still need ample musculature up front to move 
about. My vote for chief flightless pterosaur indicator would be greatly 
reduced wingspan.

~ Abyssal