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Re: Quetzalcoatlus could not jump into the air



"Dumb question:  This abstract assumes a downstroke would have been
necessary for takeoff.  Is it possible that under the right conditions
simply opening the wings at the right angle and facing into the wind
could have gotten the animal high enough for a full wingflap without
much muscular effort?"

Probably not, assuming the animals weren't the 70kg, eating
disorder-ridden individuals that Chatterjee et al. make them out to be.
Takeoff using wind alone was popular in the 1970s, when all pterosaurs
were thought to be what Paul termed something like
'ultralightairbeings', but several different lines of evidence are
pointing towards pterosaurs being much heavier than reasoned by the
previous generation of pterosaur workers (i.e. they have similar
mass/wingspan relationships to modern birds and bats). Such takeoffs
don't work at these masses.

I also don't buy the lack of space for a downstroke in a Quetz takeoff.
3-4 m would be plenty of room for a full downstroke. It's not like the
entire wing is brought perpendicular beneath the body. Indeed, if Quetz
had a flapping mechanism similar to modern animals, the humerus wouldn't
rotate much beneath the horizontal.

As Mike said, the Chatterjee et al. argument does seem to be a rehash
of their 2004 arguments and I don't think they've actually provided any
reason to doubt the recent work on pterosaur mass or launch. The
Discovery news asked for my opinion on this yesterday, and I've posted
my (long winded) comments about this below.

Mark

--

These authors haven't really addressed the points of the quad launch
idea here (which I stress I did not originate, but have written about at
length with my colleague Mike Habib, who _was_ one of the brains behind
this hypothesis), and are not working with a realistic model of
pterosaur body mass. The animals in question, the 10 m azhdarchid
pterosaurs (which include Quetzalcoatlus) are extremely unlikely to have
massed 70 kg. That's just not enough tissue to fit around their
skeletons. These animals have 2.5-3 m long heads, 3 m necks, torsos as
large as an adult man and walking limbs 2.5 m long (the wing finger,
comprising the distal portion of the wing, adds another 2.5 m to the
forelimb). Their skeletons weigh the best part of 20 kg on their own,
which leaves 50 kg of soft-tissue to cover a giraffe sized skeleton.
50kg of tissue around a 5 m tall animal leads to one atrophied
pterosaur! A number of workers using different mass estimation
techniques are now arguing that 200 kg or more is a realistic mass for
these giant animals, which is still very light for an animal of those
proportions, but allows for more generous and realistic distribution of
soft-tissue.

Secondly, the suggestion that there is insufficient muscle power in
pterosaur wings for rapid flapping is also questionable. Quetzalcoatlus
has room for about 50-60 kg of flight muscle around its shoulders, which
gives it a similar flight muscle to body mass ratio to modern turkeys,
swans and bustards. These birds are very powerful launchers with
exceptionally big flight muscles (they have to be, because they are so
heavy). Calculations of flight muscle energy output suggest that launch
for Quetzalcoatlus was no more strenuous than it was for these birds,
even at higher masses, and could sustain powerful flapping for at least
90-120 seconds.

Finally, it's ironic that Chatterjee and Templin mention scaling as a
problem here, because they have negated to challenge the most important
concept in the quad launch hypothesis: the scaling of limb bones. Bird
hindlimb bones become proportionally much larger with body mass, because
the increased mechanical stress of launching at larger body masses means
the hindlimb bones must be much stronger. By contrast, bird wings are
rather slender, as the forces incurred in flight, even at large size,
are much less than those incurred in takeoff. If pterosaurs launched
with their hindlimbs, like birds, their limbs woul
d show the same
scaling relationship. They don't. Instead, like quadrupedally launching
bats, their forelimb bones get proportionally bigger with body size,
while their legs remain slender. Mechanical testing of pterosaur leg
bone strength suggest they would buckle if they were used in launch
alone, but their forelimbs are incredibly powerful. The upper arm bone
of a Quetzalcoatlus could nearly 500 kg before breaking. 



--

Dr. Mark Witton
www.markwitton.com
Lecturer
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk

If pterosaurs are your thing, be sure to pop by:

- Pterosaur.Net: www.pterosaur.net
- The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
- My pterosaur artwork: www.flickr.com/photos/markwitton 


>>> Ronald Orenstein <ron.orenstein@rogers.com> 11/8/2012 5:14 PM >>>
Dumb question:  This abstract assumes a downstroke would have been
necessary for takeoff.  Is it possible that under the right conditions
simply opening the wings at the right angle and facing into the wind
could have gotten the animal high enough for a full wingflap without
much muscular effort?



Ronald Orenstein
1825 Shady Creek Court
Mississauga, ON L5L 3W2
Canada
ronorenstein.blogspot.com


________________________________
From: Ben Creisler <bcreisler@gmail.com>
To: dinosaur@usc.edu 
Sent: Thursday, November 8, 2012 11:53:30 AM
Subject: Quetzalcoatlus could not jump into the air

From: Ben Creisler
bcreisler@gmail.com 


A talk at the GSA meeting and a new story:


https://gsa.confex.com/gsa/2012AM/finalprogram/abstract_205827.htm 

FLIGHT-INITIATING QUADRUPEDAL JUMPS IN THE GIANT PTERODACTYLOID
QUETZALCOATLUS: FACT OR FANTASY?
CHATTERJEE, Sankar, Geosciences, Texas Tech University, 3301 4th
Street, Lubbock, TX 79409-3191, ALEXANDER, David E., Ecology &
Evolutionary Biology, University of Kansas, 2041 Haworth Hall, 1200
Sunnyside Avenue, Lawrence, KS 66045, and TEMPLIN, R. Jack, 2212 Aster
Street, Ottawa, ON K1H 6R6, Canada, jtemplin@rogers.ca 
Large pterosaurs could takeoff from an elevated perch by diving into
the air to initiate flight, but to take off from level ground was
arduous. Our estimated mass of the giant Quetzalcoatlas from the Late
Cretaceous Big Bend National Park of Texas is about 70 kg, which is
close to the theoretical upper mass limit for a flying animal.
Quetzalcoatlus could run bipedally downhill to pick up flying speed, a
technique used by albatrosses and hang glider pilots. It has been
proposed recently that Quetzalcoatlus with a new calibrated mass of
250 kg was capable of initiating flight directly from the ground using
forelimbs as a catapult similar to the style of common vampire bat (~
25 g). One issue is scaling. What is possible for a lightweight bat
appears impossible for a 10,000 times heavier pterodactyloid, which,
due to surface-to-volume ratios, will have approximately 0.0
r unit mass of the bat. Another is the height
achieved by such a “pole-vault:” the maximum ballistic jump height
of
2 to 3 meters would not be high enough to allow a significant
downstroke, where most lift and thrust is produced. With a wingspan of
10.4 m, Quetzalcoatlus would not have been able to flap vigorously for
lift generation from such a jump without smashing its delicate wings
on the ground. Moreover, the animal would need about 2440 watts to fly
level after jumping; the estimated maximum mechanical power available,
however, even with a few seconds of maximal anaerobic muscle
contraction, was approximately 1600 W, far below the flying speed that
would result in crash landing. Indeed, the body mass of 250 kg itself
appears to be largely overestimated, as powered flight and ground
takeoff seem unlikely for an animal that heavy.

2012 GSA Annual Meeting in Charlotte

====

news story:

http://news.discovery.com/animals/flying-dinosaur-pterodactyl-121108.html