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Re: New bird /pterosaur flight paper in PLoS ONE



Hmm... this is an interesting conclusion. I remember an article in New
Scientist from a while back about the same thing: I don't remember being
convinced about their conclusions of pterosaur mass and flight then, and
the paper's done little to change my mind. Here's the beef:

1) This is all based on 'albatross-like animals', but plenty of
pterosaurs were nothing like albatross in wing shape or body
proportions. Capping a limit on maximum flight mass based on one very
derived group of birds would be like scaling-up a skink to estimate the
maximum masses of sauropods: they're different beasts, and shouldn't be
treated so interchangeably when it comes to scaling. 

2) There are craploads of pterosaurs with wingspans exceeding the Sato
et al. maximum flighted wingspan (5.1 m) that are clearly, clearly
flighted animals. Pteranodon springs immediately to mind: 6 - 7 m
wingspan, thousands of individuals found hundreds of miles out to sea,
enormous, seabird-like wings for soaring flight, all the appropriate
swells and crests around their shoulders for flight muscle attachment,
diddy-little hindlimbs rendering them pretty cumbersome on land...
There's evidence that other ornithocheiroids were of similar size, and
plenty - maybe most - azhdarchids were even bigger and still retain
flight-characteristics of robust humeri, huge deltopectoral crests and
all the rest of it. Sato and chums need to explain why these chaps
retain so many characters related to flight but exceed their maximum
theoretical wingspan: they suggest their conclusions support an
excellent piece of work saying that some pterosaurs may have been
terrestrial foragers, but this idea does not apply to all pterosaurs at
all, nor explain why even the biggest azhdarchids retain attributes
indicative of flight despite being over twice their theoretical
wingspan.

3) I don't quite see how they can justify their 93 kg mass for
Pteranodon and 274 kg estimate for Quetzalcoatlus: neither has
particularly procellariiform-like proportions and yet, again, Sato and
friends only use this group to extrapolate masses for these pterosaurs.
My own estimates for Pteranodon and Quetzalcoatlus based on
extarpolations of bird mass are 60 and 150 kg, respectively - quite
different from their procellariiform-alone estimates. Once again,
pterosaur morphological diversity has been ignored in favour of a
dogmatic view that they were all marine bird-like soarers. This is even
more perplexing because the authors like the idea of some pterosaurs
living inland and being strongly terrestrial in their habits: they are
aware that marine-dwelling and continentally-dwelling birds have very
different wing shapes and flight styles, right? So how can they start
talking about the maximum masses of a pterosaur group that appear to
live predominately inland? Sheesh. 

I guess I could go on about the general lack of consideration for all
sorts of recent work on pterosaur mass and flight (they could really do
with a copy of Mike Habib's Zitteliana paper, for instance - how can
they explain the stupidly-robust humeri of big pterosaurs if they're
doing little more than standing around on them?), but it would be very
rambly and moany, so I'll stop there. Bottom line: not very impressed
with the results or methodology. If I can be bothered, I might write a
proper rebuttal. In the mean time, I should really get on with some
genuine work. That said, the university cafe is offering free food...

Mark

--

Dr. Mark Witton

Research Associate
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 


>>> Andy Farke <andyfarke@hotmail.com> 29/04/2009 21:33 >>>

Sato K, Sakamoto KQ, Watanuki Y, Takahashi A, Katsumata N, et al.
(2009) Scaling of Soaring Seabirds and Implications for Flight
Abilities of Giant Pterosaurs. PLoS ONE 4(4): e5400
.
doi:10.1371/journal.pone.0005400

Abstract:
The flight ability of animals is restricted by the scaling effects
imposed by physical and physiological factors. In comparisons of the
power available from muscle and the mechanical power required to fly,
it is predicted that the margin between the powers should decrease
with
body size and that flying animals have a maximum body size. However,
predicting the absolute value of this upper limit has proven difficult
because wing morphology and flight styles varies among species.
Albatrosses and petrels have long, narrow, aerodynamically efficient
wings and are considered soaring birds. Here, using animal-borne
accelerometers, we show that soaring seabirds have two modes of
flapping frequencies under natural conditions: vigorous flapping
during
takeoff and sporadic flapping during cruising flight. In these
species,
high and low flapping frequencies were found to scale with body mass
(mass*0.30 and mass*0.18) in a manner similar to the predictions from
biomechanical flight models (mass*1/3 and mass*1/6).
These scaling relationships predicted that the maximum limits on the
body size of soaring animals are a body mass of 41 kg and a wingspan
of
5.1 m. Albatross-like animals larger than the limit will not be able
to
flap fast enough to stay aloft under unfavourable wind conditions. Our
result therefore casts doubt on the flying ability of large, extinct
pterosaurs. The largest extant soarer, the wandering albatross, weighs
about 12 kg, which might be a pragmatic limit to maintain a safety
margin for sustainable flight and to survive in a variable
environment.

Available for free download at:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0005400


Andy

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