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Re: Chaoyangopteridae




----- 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