Re: Tiktaalik (ptero flight)

[Michael Habib <mhabib5@jhmi.edu>]

> There's no particular problem in getting the big guys off the ground.  
> They don't appear to me to launch like birds, and skeletal bracing in 
> the more heavily loaded ones appears to me to be oriented more toward 
> launch loads than flight loads.

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.

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).

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.  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).

Cheers,

--Mike Habib

*For those wondering where the heck I'm getting such information, the 
stress/strain data is my own, first presented at SVP 2005.  More info 
(in the form of full papers) will be forthcoming in the reasonably near 
future.