Re: Chaoyangopteridae

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "Michael Habib" <mhabib5@jhmi.edu>
To: <jrccea@bellsouth.net>
Cc: <dmu1@leicester.ac.uk>; <dinosaur@usc.edu>
Sent: Sunday, June 01, 2008 7:00 PM
Subject: Re: Chaoyangopteridae


> However, this assumes that 1) the forelimb muscle mass is highly anaerobic 
> (expected for a large flyer, but obviously not known)

There is secondary evidence that supports anaerobic launch and mostly 
anaerobic flapping.  Pterosaurs had very small torso volume compared to 
their overall mass, implying small lung volume, and several had enormously 
long necks for that body size, implying large dead air volume when 
breathing.  They would not have been able to supply the muscles with enough 
oxygen for continuous flapping (probably related to the flap-gliding 
scenario that most, if not all, pterosaurs used).  A high percentage of 
anaerobic muscles and the flap-gliding flight may have been what allowed the 
development of the extraordinarily long necks in spite of the dead air 
volume.

As an aside, this makes me wonder if pterosaur ancestors came to flight 
before they developed endothermy.  Pterosaurs seem to be endotherms who use 
an exothermic mode of soaring flight.  Without endothermy, they would be 
limited in the altitudes that they could achieve (due to the adiabatic 
cooling of the atmosphere with increasing altitude, which would make an 
exotherm lethargic or comatose at high altitude), and that would in turn 
limit their ability to use soaring flight for long distance travel.  Could 
the development of endothermy in  presently unknown pterosaur ancestors have 
been related to a need to go intermittantly to altitude during travel?

> and 2) there is some modest elastic storage in the forelimb tendons.  In 
> reality, my estimate here is a bit conservative, because I don't allow the 
> animal much above 120% elastic storage.  That may seem high, but dedicated 
> jumpers (such as galagos and frogs) get 700%+ in combined elastic and 
> counter-movement pre-load advantage.  Given the length of the pterosaur 
> forelimb, and several specific features of the osteology, I suspect that 
> pterosaurs probably managed a fair bit of preload (better than I'm giving 
> them).

Yes.  Again, in the specific case of quetz, the long, relatively 
inextensible neck and head require that the forefeet (hands) be placed well 
in front of the shoulders just prior to and during launch initiation in 
order to maintain the cg within stable limits.  This also serves to maximise 
available stroke length from the forelimb.  Assuming a launch angle of 30 
degrees more or less from the horizontal, much of the initial hindlimb power 
and motion would have gone into placing the forelimbs into adverse 
mechanical advantage, preloading them as the shoulders move forward relative 
to the hands.  As the hindlimbs neared the end of their extension stroke and 
the hindlimb power started to fade, the shoulder would have been moved 
forward far enough relative to the hands to allow the forelimb to start 
releasing the preload as the forelimb took over production of launch power. 
I would also anticipate a couple of  hindlimb 'fanny squats' prior to launch 
initiation, in order to preload the hindlimbs, though to a lesser degree 
than the forelimb preload. I've not attemped to quantify the elastic 
storage, but I think it is well above 120%, at least in the larger 
pterosaurs.
JimC