Re: pteros have lift-off

[Michael Habib <mhabib5@jhmi.edu>]

David Peters wrote:

> Not so. I'm working with the small Quetz. Torso same size as 
> Istiodactylus. Smaller Zhejiangopterus had an even smaller overall 
> size. Same overall proportions as the mid-sized Quetz. Not sure we 
> have any complete giant pterosaurs. All such reconstructions are 
> scaled-up versions of the man-sized ones and smaller, are they not?

Well, we have a good forelimb for Quetz northropi.  But in any case, 
this goes back to my earlier observation that azhdarchids are 
disproportionately good launchers among pterosaurs.  This likely had 
something to do with launching away from danger in inland environments. 
 The evolution of the azhdarchoid flight apparatus and launch system is 
actually quite interesting.

> Mike, everyone knows in birds they start in the folded position, 
> basically laterally. Out and up or up and out. In your scenario, 
> pteros start with the folded position, basically ventrally and on the 
> ground. BIG difference.

It's actually not a big difference, it just looks that way at first 
glance.  It's the difference of one upstroke, maximum (probably part of 
an upstroke, since flapping amplitude in pterosaurs seems to be 
relative small).  Even for a large pterosaur, that's a timing 
difference of a couple tenths of a second or so.  Given how much higher 
they leap using the quad launch, the extra time is more than made up 
for.

> >
> So pteros go from a complete down position at the moment of becoming 
> airborne to an up wing position prior to apogee? That's one heckuva 
> leap.

It's big, but not as large as you might think.  The wing moves a lot 
faster than I believe you're giving credit for.  Even for a giant, like 
Quetzalcoatlus northropi, the flapping frequency in cruising bursts was 
probably just over 1 Hrz, which means that a reduced-span upstroke, 
under heavy anaerobic power, at max speed, is only a couple tenths of a 
second.  That's slow for a flying vertebrate, of course, but pretty 
quick overall.  Flying animals are fast.  Much faster than I think most 
people realize.

>  Do you start at the zero point measuring acetabulum or glenoid 
> height? And how many of these height units does your favorite 
> pterosaur have to achieve in the first leap?

I use the cg, but glenoid works as a marker, too.  For a 200kg Quetz 
northropi launching at 30 degrees from the horizontal, I get a cg 
elevation (or glenoid elevation) of 3.34 meters from the resting line 
(i.e. its a somewhat larger number taken from the beginning of the 
unload).  Impressive, but hardly supernatural.  And more than enough 
for clearance on the downstroke.

> How fast do your calculations say a few particular pteros can run 
> before they get to the femur breaking point?

Running speed to break point relationships are rather tricky, actually, 
but ballpark 6-7 m/s for a big azhdarchid, perhaps, assuming it could 
even run bipedally at all.  Nyctosaurus comes in very wimpy, of course; 
probably under 4 m/s.  But to be honest, I've mostly worried about 
bipedal leaping ability, because that's much more telling than running 
speed for several reasons (see below).

> Googling "Albatross take-off" and "Swan take-off" both seem to show 
> the wings being held high, never dipping below the midline of the 
> bird, sort of an upper half-only flight stroke. Valid or no? I don't 
> see any real leap here except that the albatross runs off the cliff, 
> falling to gain speed then it's flying. Important observation here? I 
> see an analogy in pteros, depending on species.

I think it's safe to say that pterosaurs were not running off cliffs to 
launch (not that this is required for albatrosses, either).  In any 
case, in running launchers, the wings are elevated early, but the same 
basic principle holds as in leaping launch: the wings are elevated by 
the time the animal leaves the ground for biped launchers.  In quad 
launchers, it happens just after the leap.  So there is the difference 
of a single upstroke in timing.

More to the point, though, running-launch birds takeoff the way they do 
mostly as an adaptation to water launching.  You'll notice that they 
are almost all semi-aquatic species with webbed feet.  They also have 
short, stout femora, gracile humeri, low pectoral fractions (relatively 
speaking), hindlimbs shifted posteriorly, and high wing loadings.  Only 
the last one matches with pterosaurs.  It is not really a matter of 
size, nor it is a great way of building up flight speed, per se.  Even 
in the running launch, the last moment is essentially a small leap 
(though it isn't obvious in most videos).

Besides, we still have the same problem as before: they animal must 
provide most of the force with the hindlimbs, and most pterosaurs just 
aren't built for that.  Many simply can't do it at all.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu