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Re: Pterosaur size
On Wednesday, December 13, 2006, at 12:13 PM, don ohmes wrote:
Why does relatedness make a difference? Basic dragonfly design. Big
then, small now. Why? And you're just guessing anyway, about kinship.
Not that kinship is relevant.
Kinship is very relevant. If you want to do a trend analysis, you have
to consider the phylogenetic non-independence of the units you are
comparing. Most of the trends you refer to are, as best I can tell,
actually the result of clade-specific mechanical differences. If you
wish to demonstrate that the trends are, in fact, not a product of
clade membership then you must correct for kinship. Essentially, you'd
have to either show the trends within lineages with low functional
variance, or utilize independent contrasts. In all likelihood, you'd
have to do both. --MH
Kinship is irrelevant, although frequently there, especially at any
given point in time. _Functional equivalents_. They are probably
related, but so what?
See above --MH
Great category. But again, relatedness doesn't count, although
probably helpful in determining functional equivalence. What is the
largest ectothermic herbivore now? Then? How do they trend through
time? Those are the questions that are relevant.
It is relevant, but the full question is "how does the size of
ectothermic species trend over time accounting for phylogenetic
relatedness and functional differences?" It is very interesting; it is
also very difficult to approach and much more complicated than plotting
simple raw values against time.
Unlike Jim and Mike, I don't think today's environment could evolve a
Quetz-sized volant. Or tomorrow's environment either.
I'm still not clear on why you think this is the case. Is it
constraint from an evolutionary standpoint, or mechanistic? You seem
to imply in several cases that you feel it is mechanistic. Can you
explain what mechanical factors suggest to you that Quetz would not be
viable today? Because I cannot find anything to suggest this.
Landing, launch, and steady state are all feasible for Quetz in a
modern atmosphere (which, as was previously mentioned, isn't really
that different from the Cretaceous atmosphere from the perspective of a
large-bodied flyer at a relatively high Re). --MH
In fact, I think the current size limit for flapping flight is below
Argentavis, and somewhat above the largest birds living...
Which I find odd, because the most recent mega-volants died in the Late
Pliocene. From the perspective of the atmospheric effects you cited
before, that is modern. Argentavis might not be viable from a food
perspective standpoint, but that's because we don't have a full
megafauna at the moment. --MH
Plot the largest aquatic air breathers through time. Do the same for
terrestrials. Very different charts. Opposite slope, for one thing.
Different "lifespans" and evolutionary rates, too. Or so it appears to
Good question, but you first need to correct for kinship and make sure
the trends are real. --MH