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Re: Massive answer to the mess of pterosaur mass
Some comments on the pterosaur mass issue (specifically the Quetz. mass issue).
I think Mark's mass estimate technique has a lot of merit, and I have run some
launch calculations with his 250 kg Qn that came out reasonably well. I have
tended to prefer a slightly lower mass (closer to 200 kg) myself, but that
margin is actually a lot smaller than it seems. By the same token, my mass
estimate and Jim's are also not actually so far off as they might seem, given
how much estimate error there can be.
I do think that Jim's estimate is a bit on the low side; he and I have actually
discussed this a bit already, and our disagreement in this regard is minor in
the big scheme of things. One reason that I find a greater mass (around 200
kg) is because my planform has a somewhat lower aspect ratio and slightly
greater area. Thus, my version is more optimal at a greater mass. I also note
that extrapolating a mass of Quetzalcoatlus from the span:mass regression on
Greenewalt's bird data (with most passerines removed for several reasons)
yields a mass estimate of just over 200 kg. Calculating the mass of Qn such
that the span loading is the same for a wandering albatross also gives me a
mass of 200kg, using the albatross data I have on hand. I actually might
expect that to be an underestimate because the span loading is probably a bit
higher for large pterosaurs than large birds, based on both build and
allometric effects. The caveat there is that body weight in long-distance
travelers like albatrosses varies a great deal just within individuals. Thus,
while I get about 200 kg using the average, the estimate can swing a great deal
using a heavily fueled versus skinny set of animals.
I do think that the torso may be a bit larger than Jim gives credit for, though
perhaps I'm just reading into his analogy of a large football player too much.
While the torso was quite short, my estimates suggest that it should be quite
deep, as well, and the overall dimensions of the pectoral girdle would be
impressive, to say the least. The humerus is truly massive; anyone who has
seen it on exhibit (or up close) knows what I mean. That one element would
almost fill my thorax and abdomen (though I grant I'm a small person). The
scapulocoracoid would need to be quite deep, and the flanges quite expanded.
The precise allometry is difficult to calculate, but my rough estimate is that
the football player would have to be a very good sized linebacker at least :)
Add in the huge limbs and giant neck and head, and you have a pretty darn big
I've also started toying with some bone cross-section techniques for estimating
mass, but this is harder than it sounds because we have little a priori reason
to assume a specific safety factor for pterosaurs. It was probably near that
of birds, but we cannot say for certain. Interestingly, my first swing at that
gave me a (admittedly rough) mass of about 220 kg. The interesting thing there
is that the technique would be expected to give the maximum (ie. heavy fuel
load) weight. As such, I wonder if perhaps Mark's method does the same, and
that our estimates are more congruent than they seem (with 250 or thereabouts
being the maximum fueled mass for a large animal).
Regardless, the real punchline, I think, is that these large pterosaurs were
not the "ultralights" that is often expected. Clearly, they were reasonably
heavy animals with plenty of power generation. This holds whether Qn was a 150
kg animal or a 250 kg one.