[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Pterosaur take-off movie on the NG site
David Peters wrote:
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.
In other words, you disagree with the prior interpretations and
published a manuscript with your observations, which is great.
However, my argument was that the issue was contentious, not that a
narrow attachment had to be wrong. I think your contentions above
rather demonstrate what I was pointing out.
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.
Interesting stuff, and I'd be happy to see your reconstructions.
However, I can't exactly just ignore the published illustrations based
on your good word, either.
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.
They bear some weight, but likely not much (see below). I did not
suggest that the free digits bore no weight, except in Nyctosaurus,
and *perhaps* in ornithocheirids. We used a reconstruction, produced
by the AMNH, in which the fingers did not touch the substrate. An
alternative reconstruction might be more accurate from an osteological
standpoint, and perhaps we will do other versions down the road from a
illustrative standpoint. Little to no effect on the calculations of
the launch, however.
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.
This is rather more extreme than simple area relationships are likely
to produce. There are even slumps associated with displaced stream-
edge material from the manus push.
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.
Actually, the exchange was:
DP: 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.
MH: See above. The fourth metacarpal/phalanx joint was likely taking
a lot of the weight. Not only is this apparent in trackways, but we
did not shorten the fingers; the proportions were based upon
reconstruction of AMNH 22555. Because there is some estimation
involved, it could be that the fingers were a bit longer in life than
we estimated, and could grip the ground to some extent, rather than
lying above the surface.... Even presuming, for a moment, that this is
the case, I can say with confidence that digits 1-3 did not take much
of the weight not accommodated by the hind limbs, as these small
digits are not structurally capable of doing so.
DP: Show me some pterosaur tracks in which digits I-III are -not-
taking the weight. They -are- structural capable. Ichnites show it.
You were the one that originally argued for a full weight load on the
free fingers, which is not structurally feasible for many species, and
is not suggested by ichnites. If your argument is, instead, that the
free fingers took some weight in many taxa, then I agree. However,
they likely did not take a great deal (see below).
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.
I think you may be attributing too much area to digits I-III. One
problem with ichnites is that they can be tough to interpret, and are
very qualitative when it comes to things like the meaning of
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
Tracks are informative in some ways, but vague in others. Tracks do
not give a clear and precise idea of weight distribution at the level
you are suggesting, except in exceptional cases (such as some leap or
sprinting tracks where weight distributions are extreme). There is an
averaging effect, but there is also a lot of slop. Track
interpretation has quite a bit of qualitative and subjective
assessment. Not so much that tracks can't be used; they're a great
source of information - but exact weight distributions are not easy to
get out (Gatesy (2003) discusses this, as I recall. Other
experimental designs have also shown the complexity of track
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
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!
I am talking about derived taxa, for the most part. However, we don't
have any reason to assume a bipedal launch for more basal taxa,
either. Remember, there is no "default" - to get the answer, a
quantitative analysis is needed. I know of no quantitative analysis
of launch ability in basal pterosaurs, but I have completed a launch
analysis for several, relatively distant, pterodactyloids. The most
parsimonious conclusion, at present, is therefore that the quad launch
is the basal state. However, as someone that rather distrusts such
off-handed bracketing, I'll simply analyze the basal forms to check.
I have done some anurognathids, incidentally, and they are still
consistent with quad launching, though they are less constrained. In
lieu of any evidence *for* a biped launch, the best explanation is
that they quad launched, as well.
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.
They are not very able for most taxa. Pterosaur fingers are not much
like Desmodus fingers. Digit III might add some power in a few of the
little guys, like anurognathids. Emphasis on might. The finger that
could, structurally, push off the substrate is actually digit IV. I
expect that only the flexor tubercle actually did any pushing, but
others may find evidence that more of the wing finger touched during
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.
The elbow provides most of the power; MCIV provides mostly lever
length. However, the wrist can provide a larger moment than you are
probably given credit for, even with limited excursion. I haven't
found anything to suggest that the forelimb power was insufficient for
a quad launch in any taxa, so far. I welcome quantitative evidence to
As for the wing opening, we discussed this previously: the wing finger
does not open until later in the launch. Just let it stay mostly
closed until well into the first upstroke. That's all it needs to
do. Remember, wing clearance is *improved* by quad launching. A
biped launch has a lot of clearance issues for large species, while
quad launching does not. There is no problem with clearance - the
cost comes in timing. To be effective the quad launch needs to add
enough power to make up for the extra half-stroke timing penalty.
This is a relatively easy calculation to run, with a few basic
assumptions about forelimb power, and the resounding answer is that
the extra power more than makes up for the small timing cost. Not to
mention that for many species, no other launch will work.
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.
Well, I wouldn't consider any of the above particular similar
kinematically, I was just making a general point about antagonists and
figured it was a fun example. If we really wanted to get into the
mechanics of striking then we should be comparing circular kicks with
long-arm strikes and thrust kicks with jabs, etc. But I think that's
a different sort of forum. :-)
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 starters.
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 Bess.
No, it's not good. I would not consider the thighs of most large
pterodactyloids to be "massive", but subjective usage aside: no, the
thigh musculature does not make it better. Actually, muscles usually
generate much larger input forces than output, because they work with
a negative advantage lever arm. As such, the added musculature
further decreases the safety factor for the femur. Muscles don't load
as rigid elements in compression or bending, so they do not take
weight off the femur - they do, however, impart substantial forces
upon it. And no, based on bone strength analysis, most of the larger
taxa probably could not run bipedally. Many could gallop or canter
quadrupedally, I suspect. I actually agree that Pteranodon would have
a hard time walking on its hind limbs, though not because they would
fail. The limbs would fail under the required launch loads, however,
if they were the only (or primary) propulsive unit.
Assistant Professor of Biology
Woodland Road, Pittsburgh PA 15232
Buhl Hall, Room 226A