Re: Tiktaalik (ptero flight)

[jrc <jrccea@bellsouth.net>]

Comments inserted below.
Jim

----- Original Message ----- 
From: "Michael Habib" <mhabib5@jhmi.edu>
To: <dinosaur@usc.edu>
Sent: Thursday, April 06, 2006 6:24 PM
Subject: Re: Tiktaalik (ptero flight)


> And, in fact, heavy bracing seems to be related to launch loads in many 
> birds, as well.  Bone stress and strain both seem to be lower in the 
> forelimb infrastructure of endurance fliers, and higher in those that use 
> bursting takeoff *.  The trend needs further investigation, however, and 
> is undoubtedly more complex than it currently looks.

I agree wholeheartedly.  I do note that in my scenario for quetz launch, the 
front feet (hands) are the last thing to leave the ground, and when they do 
leave the ground, the beastie is already going faster than steady-state 
stall speed.  The outer wings seem to me to be unfolded after the arms are 
raised high enough that the wings can unfold without the tips whacking the 
ground.  After that, the rest of the upstroke is pretty much standard.  On a 
'good' day, no flapping would be required.  On a 'bad' day, perhaps 10 to 20 
flaps would be required, before an extensive break.  I doubt that quetz 
could flap for a protracted period because the volume of the trachea seems 
to me to be fairly substantial compared to the probable volume of the lungs, 
implying that there might be a limit on continuous rates of oxygen exchange.

> The exception is wing-propelled aquatics, which have the heaviest bracing 
> of all, but that's presumably a fluid medium issue (as well as a 
> thrust-producing upstroke issue).  Overall, the launch strategy vs bone 
> stress pattern is interesting because forelimb (and sternal) robustness in 
> fossil species is sometimes used as an indication of poor vs advanced 
> flight ability.  In reality, gracile forms may just be endurance fliers, 
> with poor launch but strong cruising flight; while those with heavy 
> bracing and/or high-load adapted limb geometry may be adapted to rapid 
> launch.  Rapid launchers can be long or short distance fliers, depending 
> on other factors (for example, compare a grouse with a pigeon).

Agreed.  Particularly re birds.  Two thoughts come to mind.  Quetz bracing 
throughout the skeleton is fairly consistant and isn't all oriented to match 
flapping loads or soaring loads. And launch doesn't appear to necessarily 
involve flapping anyway.

> Of course, the neat thing about Qn and Qsp is that they seem to combine 
> rapid launch ability with high efficiency burst-flapping flight, which 
> would seem to make them (and possibly a few other pterosaurs) the only 
> rapid-launch supersoarers.

You're a good man, Charlie Brown.  I agree again.  They do have an 
extraordinary ability for high efficiency burst-flapping flight (as well as 
rapid launch capability), but my take is that quite often they wouldn't have 
had to use the burst-flapping mode.

>  None of the modern avian soaring champs have particular rapid launch 
> ability (vultures take off from a standstill, but the takeoff velocity 
> isn't all that high...they just have a low stall speed).

True.  And though quetz (and most other pterosaurs) would seem to have been 
able to achieve maximum lift coefficients substantially higher than any 
birds, quetz stall speed wasn't low -- they were heavily loaded.  Some 
other, more lightly loaded pterosaurs would have had a relatively low stall 
speed.
> Cheers,
>
> --Mike Habib