Re: L'origine et l'évolution des oiseaux, with a twist

[jrc <jrccea@bellsouth.net>]

Comments inserted
JimC

----- Original Message ----- 
From: "David Peters" <davidpeters@att.net>
To: "jrc" <jrccea@bellsouth.net>
Cc: <dinosaur@usc.edu>
Sent: Thursday, January 29, 2009 4:28 PM
Subject: Re: L'origine et l'évolution des oiseaux, with a twist



> The beauty is, it's never slack. Embedded with chord-wise fibers, so 
> virtually no flagging.

If chordwise and stiff enough to inhibit flagging, they have to function as 
compression battens like a bat's fingers.  I suspect that they don't have 
significant compression capability due to excessive length/dia ratio.  I 
would expect them to operate in differential tension more like a pterosaur 
patagium and would expect the distal pattern to be more nearly semi-spanwise 
than chordwise, again more like a pterosaur.

> > As an aside, a strut with a thickness of about 2 inches
> > will usually have a chord of roughly about 4 to 6 inches.
> > For the same drag, struts are a lot bigger than circular
> > dragwires.

> I'm not shooting for similar drag ratios. Simply less drag. And really, 
> drag is not the issue while running in this taxon, not as big a deal, as 
> every step is another unit of thrust. And the >uropatagia become wings when 
> lateral.

I agree with that last sentence.  :-)

> The key to this thread is long legs (longer tibia than femur) = cursor.

Possible, but not a given.

> Not sure about leaping, other than that last arboreal fling before 
> becoming airborne.

Why would you expect them to run to takeoff speed ?  Like most everything 
else that small, it would appear at first blush that they could probably 
leap to takeoff speed.  If so, why do it the hard way.

> All sister taxa tracks (Rotodactylus) indicate narrow-gauge, often bipedal, 
> proximal phalanges elevated along with metatarsus-type locomotion.

> David Peters
> davidpeters@att.net