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RE: Chaoyangopteridae




Comments inserted below:

> Date: Mon, 2 Jun 2008 06:38:21 -0600
> From: jrccea@bellsouth.net
> Subject: Re: Chaoyangopteridae
> To: mhabib5@jhmi.edu
> CC: dinosaur@usc.edu
>
>
> ----- Original Message -----
> From: "Michael Habib" 
> To: 
> Cc: ; 
> 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.

What about long necked birds such as swans and flamingos? Swans in particular 
are interesting in this regard, since they not only exhibit large tracheal dead 
space but are known to fly at considerable altitudes.

>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.

I regard endothermy and its resulting elevation of aerobic power as an 
essential precondition to the development of powered flight.  I don't believe 
it's any coincidence that all living vertebrates which fly have both.  Even 
insects have endothermy of a sort (the whole insect may not be endothermic, but 
the flight muscles are.)  The aerobic power seen in bats and birds are not just 
average levels, but well above average compared to most terrestrial mammals and 
birds.  Bats are particularly telling in this regard, since their lungs are as 
"birdlike" as it is possible for a mammalian lung to be, and their capacity for 
aerobic power production is matched by very few land mammals, such as 
pronghorns and greyhounds.  Ectothermic flyers would be highly at risk for 
fatigue during flight, and metabolic recovery between flights would take much 
longer than an endotherm of comparable size.  Plus, fatigue during flight might 
have certain survivability consequences... :-)

Guy Leahy

>
> 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
>
>