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Re: Pterosaur size
"...Of course it is. :-) It's an overarching interpretation of a rather
large number of observations. It is thus potentially useful for
science. To find out whether it is, I must know the conditions for when
it should be considered disproven."
I disagree. NOT a hypothesis. Granted, the observations absolutely beg for an
explanation (ie, hypothesis)... to my mind, anyway. I got one, too.
"No, they died out. The Permian mega-dragonflies are not among the ancestors of
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
"I don't know if it's out of the question that the so-called *Andrias
matthewi* (the huge Miocene cryptobranchid) is the ancestor of today's
*Cryptobranchus alleghaniensis*. If so, there we have the dwindling for
this one lineage."
Kinship is irrelevant, although frequently there, especially at any given point
in time. _Functional equivalents_. They are probably related, but so what?
"Many of those groupings have a size limit. Think of rodent-like seed
eaters: if they get too big, they need to become ordinary herbivores;
too small, and they couldn't sustain endothermy."
Seedeaters? Who cares? Not me. Minimum size for endothermy? Very, very good.
Now that is interesting. Love to have some observations/datapoints. Measurement
error is a problem with minimals... which is why I haven't tried to do it.
"Let's try if I find a counterexample... big ectothermic herbivores: the
biggest turtles, the biggest pareiasaurs, the biggest captorhinids, and
the biggest caseids were all about the same size, IIRC, and I'm not
aware of any dwindling except perhaps among the pareiasaurs."
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.
"Certainly not, unless all birds die out and the bats survive it."
But then you would (wager they will eclipse Quetz)? I wouldn't. Unlike Jim and
Mike, I don't think today's environment could evolve a Quetz-sized volant. Or
tomorrow's environment either. In fact, I think the current size limit for
flapping flight is below Argentavis, and somewhat above the largest birds
living... even considering that some systems are superior to others, which to
my mind just increases the variance, but doesn't affect the slope of the moving
average. Just an opinion.
"As clear as for terrestrial vertebrates, I'd say. You might like the
fact that the biggest ichthyosaur (and probably the biggest marine
vertebrate before *Basilosaurus*) was Triassic, though -- but then it
is far from the ancestry of the later ichthyosaurs."
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 me. Why?
"Well, what goes down must come up."
"The water comes up again -- there are volcanoes that spew a lot of water
"...return mechanisms are obviously moderately efficient..." --William Fyfe. He
goes on to question the 100% return assumption. I am a little skeptical, but
have no firm opinion.
"I guess so does the nitrogen."
Almost everybody would agree. Like you, they are guessing. I have questions and
desire more reliable/relevant data. Last I checked, the methods used to
quantify the various forms of nitrogen in sediments/crust/magma are
specifically designed to _exclude_ atmospheric "contamination".
"Maybe that counts as "relatively short" or less."
Drosophilids optimize wingload in a few generations, in response to latitudinal
----- Original Message ----
From: David Marjanovic <email@example.com>
Sent: Wednesday, December 13, 2006 10:17:16 AM
Subject: Re: Pterosaur size
-------- Original-Nachricht --------
Datum: Tue, 12 Dec 2006 16:58:10 -0800 (PST)
Von: don ohmes <d_o
t of your scenario falsifiable? I'm not sure
> > it is.
> > If the biggest member of a clade is extinct, you'll say a dwindling
> > has occurred since; if it's extant, you'll say the dwindling is yet
> > to come. Right? This sounds like you would only accept cases where
> > a maximum size was reached at some point in the past _and has been
> > precisely kept ever since_ -- an extremely unlikely scenario, even
> > if only for stochastic reasons. Maybe Neosauropoda counts (the
> > Morrison supergiants + *Argentinosaurus* + *Puertasaurus*).
> Don says => It is not a hypothesis.
Of course it is. :-) It's an overarching interpretation of a rather large
number of observations. It is thus potentially useful for science. To find out
whether it is, I must know the conditions for when it should be considered
> Insects appeared in the fossil record, those insects that found size
> to be an advantage got big, then they dwindled in size.
No, they died out. The Permian mega-dragonflies are not among the ancestors of
> Amphibians appeared in the fossil record, got big, then dwindled in
I don't know if it's out of the question that the so-called *Andrias matthewi*
(the huge Miocene cryptobranchid) is the ancestor of today's *Cryptobranchus
alleghaniensis*. If so, there we have the dwindling for this one lineage.
(Remember that it's a matter of dispute if temnospondyls or lepospondyls are
> Reptiles, dinosaurs, birds, then mammals all have done the same.
What, if anything, is a "reptile" then?
> Really, it has more to do with functional equivalences, wherein systems
> are grouped by process. Egg layers, flying vertebrates, quadrupedal
> herbivores, all follow the same pattern.
> Can you think of any process where this pattern does not hold?
Many of those groupings have a size limit. Think of rodent-like seed eaters: if
they get too big, they need to become ordinary herbivores; too small, and they
couldn't sustain endothermy.
I don't think the pattern exists. I think it's an attempt to see a pattern
where none exists. Trying to figure out if actual descendants are bigger or
smaller than actual ancestors is a lot of work -- part of that work, for
dinosaurs, was my M. Sc. thesis.
Let's try if I find a counterexample... big ectothermic herbivores: the biggest
turtles, the biggest pareiasaurs, the biggest captorhinids, and the biggest
caseids were all about the same size, IIRC, and I'm not aware of any dwindling
except perhaps among the pareiasaurs.
> Question-- what is the length of time from first appearance to the
> all-time size champion in the groups listed above? In the genetically
> related subgroups of the groups listed above (eg, dino herbivores,
> ptero flyers, bird flyers, etc.)?
Well, is it "bird flyers", or is it "large bird flyers" (vultures, albatrosses,
pseudo-toothed birds)? Which should count?
> As to extants ("future dwindlees" : D), only bats come to
> mind. Note the age (~60 mys? that number still good?). Note they are
> a sub-group. I think they will get bigger, barring catastrophe.
Why should they? What advantage would they get from it?
> Want to wager they will eclipse Quetz?
Certainly not, unless all birds die out and the bats survive it.
> Don says => Sigh. Aquatic air breathers. Lots of different kinds,
> very long time, blue whale biggest. Teleosts. Sharks. Clams. Any
> clear patterns?
As clear as for terrestrial vertebrates, I'd say. You might like the fact that
the biggest ichthyosaur (and probably the biggest marine vertebrate before
*Basilosaurus*) was Triassic, though -- but then it is far from the ancestry of
the later ichthyosaurs.
> > > It is an entirely incorrect way of
> > > determining how much atmospheric N2 is subducting over time.
> > How should that happen?
> Don says => Qualitatively: seawater is at equilibrium w/ the
> atmosphere. Where goes seawater, there goes (some) atmosphere.
> Seawater penetrates _at least_ 12-14 km into ocean crust. Circulation
> intra-crust and subduction occurs. Exotic organisms
> but nobody knows what, and p/t/ph conditions that are suitable for
> abiotic N2 fixing are down there. Continental seds with contribution
> from the atmosphere also exist. No one questions that some N2 is
> Quantitatively: How much, and what fate are the questions I am asking.
Well, what goes down must come up. The water comes up again -- there are
volcanoes that spew a lot of water vapor; I guess so does the nitrogen. After
all I'm not aware of a volcanic rock that is a nitrate or nitrite, and nitrides
don't seem to occur in nature at all.
> Don says => N2 moves along thermal gradients (hot=> cold),
Why should it?
> The thermal gradient from the earth core to the surface
> reverses just below the surface.
> Where, logically, an average wayward N2 molecule stops, making no
> contribution to atmospheric mass.
Well, there are no nitrogen bubbles at that depth, nor any other nitrogen
stores I'm aware of...
> Also, conductivity is proportional to density, given similar
> composition. Generally, as atmospheric mass increases, latitudinal
> temp gradients decrease.
I see. Now someone should quantify that.
> > > 3). The tacit and universal assumption of steady-state atmospheric
> > > N2 mass therefore colors all evaluations and models of paleo-
> > > climate, particularly those periods of the distant past wherein CO2
> > > levels were much higher.
> > Then you have to explain why those models work pretty well.
> Don says => I do? They do? That is big news. What do you mean by
They are pretty successful at predicting the climate we find to have existed by
other evidence. Like, no ice during much of the Cretaceous, and so on.
> > I defend this by saying that, having cleared such hurdles as evolving
> > feathers and wings, the time logically needed for a volant to
> > optimize wingloading is relatively short.
> But then, *Limnofregata* is IIRC Danian, and the Danian only lasted for
> around 3.8 Ma.
> Don says => ?
Maybe that counts as "relatively short" or less.
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