Pterosaur take-off movie on the NG site

[David Peters <davidrpeters@charter.net>]

http://blogs.ngm.com/blog_central/2009/08/pterosaur-takeoff-.html


This is a great explanation, movie and illustration. Great pteroid  
placement. Finally I understand Mike Habib's thinking.  At last I see  
where the magic took place and the science left the room, even if  
inadvertent and with the best of possible intentions.

Minor problems (Tupuxuara painting):

1. When quadrupedal, the palms would be in the neutral position,  
neither suppinated nor pronated, but positioned as in clapping or tree  
grappling. When pressed against the ground then, the fingers splay  
laterally to posterolaterally. The painting of Tupuxuara has trouble  
with putting the fingers "pads  and claw tips down."

2. Chest is way too shallow on painting, should be 3x neck depth.  
Upper arms way too gracile. Beef them up!

3. Should be a shallow keel on the dentary for Tupuxuara.

4. No hair?? Too little hair? Needs more fuzz.

5. Wings should nearly disappear whenever folded. Wings don't extend  
onto the tibia, but are stretched between the elbow and wingtip with a  
fuselage fillet extending back toward the femur. No fossil shows it  
any other way.

Minor problems (Anhanguera movie):

1. Ordinarily on the ground, the knees are flexed at 90 degrees,  
extending only during leaps and in flight. Move feet beneath the  
torso. This happens when you bend the knees. Footprints show  
pterosaurs are not wide-splayed like this. (We don't have Anhanguera  
tracks, but we do have beachcombing pterosaur tracks). When the knees  
are bent the feet move further forward, beneath the center of balance  
near the shoulder joint.

2. Needs prepubic bones. I know, they're unknown in Anhanuera, but all  
other pterosaurs have them.

3. Anhanguera feet are much smaller than you show. The smallest feet  
of all pterosaurs. During the leap, the feet should elevate from heel  
to toe in sequence, delivering a final push with the tips of the toes.

4. The forelimbs are quite wide. A more efficient vector would have  
the limbs directly beneath the shoulders.

5. Anhanguera did not have a typical tetrapod gait, nor a typical  
pterosaur gait. With such short legs, the force vectors from fingers  
to shoulder could never point forward. This relegates Anhanguera to a  
weak bipedal hindlimb propulsion (knees bent) with support, not  
propulsion, coming from the wings. Like using crutches, except the  
crutch tips have to stay in front of the shoulder the whole time on  
Anhanguera. My guess is it stayed airborne as much as possible.

Major problems:

1. The narrator reports the "knuckles of the wing fingers rest upon  
the ground", but this is not so according to tracks. Only would be so  
in the case of Nyctosaurus (and pterosaurs like it), which has  
vestiges for fingers and a much longer metacarpal.

2. On the closeup view of the slipping tendon, metacarpals I-III are  
inaccurately shortened. In reality they should extend as far as the  
big wing metacarpal (#4). If this was done for illustrative purposes,  
then it cheated the whole concept. Fingers 1-3 should be larger (1/3  
of the metacarpal length in Anhanguera) with much deeper unguals (claw  
bones), further lengthened by keratinous extensions. Ordinarily, and  
pterosaur tracks show this, these three fingers take ALL of the weight  
not taken by the hind limbs. There is no deep track preservation of  
digit IV. There is no trace at all, typically, of digit IV.  If no  
weight is placed on this joint, then there is no elastic recoil and  
the hypothesis has no power source for takeoff.

3. Whenever an animal leaps into the air (think of frogs, kangaroos  
and basketball players), after the leap the legs extend straight back  
trailing the rest of the body in the line of the trajectory until they  
draw up somewhat and extend forward near the apex to prepare for a  
springy landing, lined up with the anticipated landing spot. In this  
pterosaur animation "the elastic recoil forcefully extends the  
forelimbs," but the wing finger is not forcefully extended. The  
animator holds it back, to avoid contact with the ground, which would  
have been inevitable if indeed there was an elastic recoil at this  
joint. But slamming the wing finger into the ground won't work...

4. So the elbow is forcefully hyper-extended and no distal (ground  
contact) elements are forcefully extended. When the elbow is  
hyperextended the propatagium is minimized as it is stretched to its  
limit. Birds have a ligament to prevent exactly this sort of  
hyperextension of the elbow. Bats do too.

The 1-4 sequence of an azhdarchid takeoff called "Winging it":

1. This sequence shows that all of the propulsion comes from the elbow  
joint because the wing finger is not fully extended immediately after  
take-off (according to the illustration), as it would have to be if  
indeed a recoil of this joint is operating. Here there's not enough  
coil in step #1, not enough recoil in step #2 (note the pterosaur is  
no higher after extension) and for some reason it keeps on rising in  
step #3.

Mike, sorry I didn't nail these problems earlier. I never realized you  
had shorted the fingers and metacarpals I-III to make the recoil  
pressure on the big metacarpal possible.

Best regards,

David Peters