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Re: Pterosaur take-off movie on the NG site
On Sep 8, 2009, at 11:17 AM, Mike Habib wrote:
David Peters wrote:
Actually, no fossil shows the inboard wing clearly at all;
Not true. See Peters 2002. Unfortunately, no one else since then
has shown any different.
Actually, a *lot* of people have shown differently in the
literature. Just for starters: Wild 1993; Unwin and Bakurhina 1994;
Wang et al. 2002; Lü 2002; Bakhurina and Unwin 2003; Frey et al.
2003 and Bennett 2007
Actually: no. Wild showed patches but no pattern. Unwin and Bakhurina
1994 tried to follow Sharov 1970, but got completely different lines.
My 2002 paper showed those lines to be geological faults. Wang et al.
sketched what I did in 2002 so we found the same things. They simply
described it differently to fall in line with the paradigm. Lu found
patches but no pattern. Bakhurina and Unwin 2003 is an abstract
without illustration. Frey et al. 2003. traced no wing membrane but
concentrated on veins and such details. What they describe near the
thigh of the darkwing is thigh material. The tight curve at the
anterior femur was ignored. Bennett 2007 ignored his own sketch ,
which also showed the tight little curve aft of the elbow, when
recreating his wing diagram.
Well, to really do this, we would need to be in the same room, with
the specimen. This was the case in Munich, which actually convinced
me of a hind limb attachment (of some sort) in many specimens
(though it by no means suggests that this was the case for all
taxa). It also demonstrated just how difficult it actually is to
follow the inboard wing on even the best specimens. I know that you
can supply photo outlines that seem suggestive of a more narrow
wing. I do not find them conclusive, in and of themselves. Some of
Helmut Tischlinger's UV photo work really seems to indicate that
there is some mesopatagium lateral to the tibia in some of the
specimens. I find his work to be somewhat more convincing, at this
specimen number? paper?
We can eliminate certain gaits because they don't provide propulsion.
Perhaps - have you done a biomechanical power and propulsion
analysis to constrain the potential ground-walking gaits? I've done
some, but not enough yet for publication.
I can tell when the fingers can't get behind the elbows. This occurs
only in certain cases, and in no beachcombers.
Two ornithocheirid tracks are known:
1. Purbeckopus pentadactylus (DORCM G 6664; Delair, 1963; Wright et
al. 1997) an early Cretaceous ichnite.
2. TATE 0049-06 (Southwell and Conneley, 1997) a late Jurassic
I can send you pdfs if you don't already have them. Neither has the
single deep indention you describe. Just enough room for three
They might not be ornithocheirids,
They match specific ornithocheirid pedes. Part of my studies. Don't go
by the published sketches of either. They both have errors. I can send
you revisions by request, but I only did the feet.
actually, but putting that aside: note that they are not "hollowed"
at the base of the fingers. I said explicitly that it would not be
a single, deep indentation. Instead, the mcIV/phIV joint impression
is apparent as the middle of the manus track. The bases of the
"free" fingers are confluent with the sides of MCIV. Their bases
cannot touch the substrate. Therefore, the "thing in the middle" is
not the base of the free fingers. It is the MCIV/PhIV impression.
If finger 1 provides a complete impression, not just an ungual, as is
the case, then the the fingers are being hyperextended 90º. That they
all join at the base supports that reconstruction. Yes, there's a
roundness medial to digit II. That must be digit IV. Key here is: the
fingers all surround digit IV and have plenty of floorspace alotted to
them. They are weight-bearing and get pushed into the substrate. They
were not raised as your illustrator and animator show.
It need not be especially deep. I think you presume that more
details of weight support are evident in tracks than is usually the
case. Sometimes a weight shift can be seen, but the tracks need to
be especially well preserved, and substantial weight shifting needs
to occur. Tracks are often counter-intuitive, especially if the
substrate was deep and soft (see Steve Gatesy's work with avian
There is a deepening of the manus impression in some East Coast
tracks (as yet unpublished, so I won't say more on the identity), in
what appears to be a launch sequence. That's not surprising, as it
would amount to about 2 or 3 times body weight, which is a
substantial increase and can be see in the ichnite with some clarity.
I'm looking forward to seeing those tracks when they become
available. Remember the old snowshoe example. The broader feet don't
sink as deep as the narrow ones. The fingers are smaller in area,
typically, than the feet are, so they sink in deeper. Simple as that.
Okay, let's say your resistance and recoil hypothesis worked on
hard, unyielding surfaces. Would it work on soft mud or wet sand at
all scales for all pterosaurs? Or would the substrate slip? And
along with it, the wing finger under tension?
Show me some pterosaur tracks in which digits I-III are -not-
taking the weight. They -are- structural capable. Ichnites show it.
Not true; see above. You cannot glean as much about weight support
from the tracks as you might think, though you can see a fair bit.
Again, if MCIV/PhIV was not contacting the ground, then the tracks
would have a more pronounced concave crescent.
Why are you turning this argument around? No one said mc IV is not
taking weight. I only said it is not taking -all- the weight.
This applies to essentially any trackway at all. But just for
starters, let's look at the very nice trackway just published by
Mazin et al. (the possible landing track). Look at figure 1b: note
that the manus prints are all *convex*, not concave. If you were
correct, the tracks would lack any impression in the area of MCPhIV
joint, but there is a very nice impression of it in each track.
I asked you to show me tracks in which I-III were NOT taking weight.
You have twisted the query.
Keep in mind that digits 1-3 are rooted, as it were, to MCIV. Thus,
the area in the "middle" of each track where the fingers seem to
come together must be MCIV.
Granted. Never an issue.
It is leaving an impression, and a rather large one, actually.
Actually no. When you subtract digits I-III from the "runway" tracks,
you are left with a very slender minority of the print.
As for structural capacity, a quantitative analysis of bending
strength is more informative.
No, deep impressions of tracks are more informative because they take
in all the factors including the exact weight bearing down from above.
My quick calculation indicates failure for the small digits in a
large azhdarchid trying to stand on them alone. Of course, this is
just illustrative, because what would actually happen is that the
animal would simply sink down onto the MCPhIV joint, given that the
fingers are not single rigid structures.
That makes sense. There would be failure in the human hand were we to
try to do the same thing.
I also note that articulating many specimens, especially large
pterodactyloids, into a walking posture forces the MCPhIV joint to
touch the substrate. Personally, I have been unable to find any
articulation in which digits 1-3 touch the ground and the MCPhIV
joint does not. They all touch together, except in things like
Nyctosaurus, which just seems to walk on the hind limbs and MCPhIV.
I never argued otherwise, my friend.
It's also a coincidence that the pteroid fits into the cup of the
preaxial carpal and look at what trouble that has brought to those
who move it there in reconstructions. Mike, I am following your
logic. In the end though, there's too much trouble for me to accept
this "click beetle"-like launch mechanism.
I don't see any trouble. If you wish to refute it, however, then I
am all ears. However, you will need to supply stronger evidence.
Preferably a quantitative, biomechanical analysis of structural load
capacities. If nothing else, you would need to demonstrate that an
ornithocheirid cannot place the MCPhIV joint on the ground. I argue
that it did so nearly all the time, and that the free fingers in
some taxa could barely touch the substrate.
I make this argument based on finger proportions and trackways.
However, even if my assertion is incorrect in this regard, the
catapult storage mechanism is still plausible and consistent with
morphology so long as the tendon *can* be compressed, even if it was
not locked during walking.
And you made a great presentation. Don't consider this the end,
though. Fix the problems by making them more reflective of the
reality. Your best friends in this regard are your worst critics. If
your hypothesis is real you'll be able to handle any detractors with
evidence. If you're right, you'll be able to show it. You'll be able
to handle their objections to the satisfaction of your detractors and
ultimately bring them along to your hypothesis.
I appreciate that the numbers are working on one side and not the
other. Not sure what the solution is if not gooney-bird- or pelican-
Well, I've given a plausible alternative. Actually, there is really
nothing in any pterosaur suggestive of a gooney-bird or pelican-like
launch. We have no reason to assume such a gait, and it turns out
to be impossible for all large pterodactyloids. In fact, all of the
morphological traits we would presume to exist in a bipedal, running-
launching species are not only absent in large pterodactyloids, they
trend in the *opposite* direction of what we see in water-launching
birds. The femora in large pterosaurs are proportional more gracile
than in small species, not more robust. The feet in many of the
largest pterosaurs are small, not large. The proximal forelimb is
robust, not gracile. The list goes on for a while.
Understood. But notice you're talking about increasingly derived taxa.
They are solving various locomotion and mass problems in several ways
and different from birds. I just found a pterosaur with a pelvis half
the torso length. Now that pterosaur has issues!
First of all, not all animals leap with the position you suggest.
In fact, vampire bats, the living quad launchers, don't do so.
But more to the point:
Figure 3 of The Journal of Experimental Biology 200, 3003–3012
(1997) THE DYNAMICS OF FLIGHT-INITIATING JUMPS IN THE COMMON
VAMPIRE BAT DESMODUS ROTUNDUS shows this. Figure 2 stops short of
becoming airborne. And the thumb tip is the last element to leave
the ground. I also note that the humerus is more than half the
length of the ulna and at maximum flexion the humerus and ulna are
at 90º to one another in front view. This is where the leverage is
in Desmodus. In some pterosaurs there are similar proportions. In
others the humerus is much smaller and therein lies trouble.
Yes, the limbs extend and the thumb is last to leave the ground, but
the leap is not frog-like, either, which was the gist of my earlier
comment. In any case, much of the leverage in Desmodus actually
comes from the thumb.
Then let's get those fingers involved in pterosaurs, too, at least to
the extent that they are able.
There is some from the elbow and wrist, too, of course. While the
longer humerus does increase the excursion length, it also limits
the maximum stress that the humerus can take. The shorter humerus
and antebrachium of pterosaurs gives them much greater power limits
about the elbow. The excursion length of the limb is then increased
by the long MCIV (relative to the bat). So, in both cases, there is
a shorter, stouter element that sees a lot of stress, and some
longer elements that help add excursion length. It's just that
which elements are which differ between the bat and the pterosaurs.
So once again, no trouble.
Mike, I don't have any trouble with pterosaurs leaping with their
forelimbs. I only have trouble with the height that can be achieved
when I see relatively little angulation (storage of energy) between
the elements of the wrist. And I have trouble with the opening of the
wing finger when its initial trajectory is straight down toward the
earth at take-off.
1) the wing finger *is* forcefully extended - because of its
shape, only the proximal end (the flexor tubercle itself,
essentially) actually hits the ground. The rest of the finger
does not "lay flat", as it were.
That doesn't show in the animation. If something is indeed
forcefully extended it needs to be extended to the limits of its
joint mobility. Not held back.
I already explained this: the limit of extension, in this case, is
when the tubercle contacts the substrate.
Micromoments later the tubercle is not in contact with the substrate.
Incidentally, it is also not true that anything forcefully extended
becomes ballistic in nature and goes to the limit of joint
mobility. Actually, it almost never happens - antagonists usually
fire even in powerful motions. For example, a person throwing a
kick does not (generally) fully lock their knee. For more technical
treatments, look at the myological literature - there are a lot of
nice electromyograph papers out there.
Come up with an example that is similar to leaping from the substrate.
Kicking is like eye-gouging or punching. Not similar.
2) the long flexors for the fingers also cross the wrist. Much of
the stored power goes into mechanically extending (anatomically
flexing) the wrist.
You say that, but the animation doesn't show any flexing of the
wrist prior to launch. Only extension after launch.
Well, if it extends, then there is the power. We show a bit of
flexing prior to launch, but not a great deal, as we have it
starting in a highly flexed position.
If it's always 'cocked' is it really 'cocked'? Have your animator
relax the wrist before cocking it. That will go over better.
I'm looking forward to seeing the evidence for implantation of
digit IV in the substrate. Shoot it my way when you can. That's
key. If you can't provide it, there may indeed be problems.
See above. Again, there are multiple ways this can work, which are
all feasible. By contrast, I have yet to see any positive evidence
for a biped launch, and I can supply a lot of negative evidence.
The femur snapping in large species is a pretty good one, just for
Femur snap? Well, that's not good. Surrounded by a massive thigh in
perfect coordination with two of the limbs taking the weight off the
femur? and it can't run? I'm getting a Whitfield and Bramwell deja vu.
Remember, they said Pteranodon could not even walk on its hind limbs
and would have been relegated to a small wheeled wagon, ala Porgy and
Thanks for the thoughts. I am your best friend. And you will have a
fool-proof hypothesis when you're done.
Best regards, and congratulations on all the great PR.
Thanks very much; I appreciate it.
Assistant Professor of Biology
Woodland Road, Pittsburgh PA 15232
Buhl Hall, Room 226A