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Re: late night thoughts: misunderstand what?

----- Original Message -----
From: "don ohmes" <d_ohmes@yahoo.com>
Sent: Sunday, June 17, 2007 1:42 PM

............ No, we are still in disagreement. Employing that most valuable analytical and
communicative device, the cartoon-- Assume a predation pair; an herbivore w/ a red kill switch on it's neck,
and a carnivore w/ one finger. If an encountered carnivore is not tall enough
to reach the button, or close enough to detect it, the herbivore survives. If a
carnivore cannot find an herbivore that is short enough to kill, he dies.
Assume respective height variances and other variables such that selection for
height occurs; in other words a classic "arms race".

Fair enough, but keep in mind that this scenario makes a testable prediction:

### The maximal, average, and minimal sizes reached by sauropods should increase throughout sauropod history, unless there is an upper limit to sauropod size at which the increase of the maximal size has to stop, in which case the mimimal size should reach it very soon after the maximal one. ###

This prediction has been tested often enough (Carrano 2005, Hone 2005, me unpublished, Carrano 2006), and has not survived any of the tests. If we ignore the Late Jurassic *Amphicoelias fragillimus*, which is a size class of its own according to the latest estimates, the maximal size is reached in the Early Cretaceous with animals like *Turiasaurus* and continues to the end in animals like *Puertasaurus*; but the minimal size does _not_ increase during the same time: there were plenty of small saltasaurids in the Late Cretaceous, the small *Amargasaurus* in the Early Cretaceous, and *Brachytrachelopan* in the Late Jurassic, all smaller than a self-respecting elephant bull (and IIRC a bit smaller than the Middle Jurassic *Shunosaurus*, which was considerably smaller than the contemporary *Omeisaurus*). The average does not increase either; if anything, it decreases (though that's not statistically significant either according to my incomplete unpublished results). The range of sauropod sizes seems to have increased, not decreased, and to have increased downwards, not upwards. I think we can end the discussion right here.

In the quadruped vs biped case, the height gained by the quadruped

...always assuming a horizontal neck...

is accompanied by a proportionally
larger mass gain than is the case w/ the biped, ultimately placing the
quadruped at a disadvantage.

Why is mass a disadvantage in fighting?

When the herbivore hits it's mass limit,

That's not a "when", that's an "if". It has been calculated that at 140 tonnes the legs of a land animal must be so thick that they must touch in the midline; the latest estimate for *Amphicoelias fragillimus* is 122 tonnes.

Interestingly, there's also a theropod that is more or less a size class of its own, but that is *Spinosaurus* -- an animal that certainly got more of its food from fish than from sauropods.

soon there are carnivores are tall enough to reach the switch of every herbivore, as
directional selection is still occurring on their side of the equation. Classic
arms race, and the carnivores won. After all, all they had to do was lengthen
one finger, and maintain enough locomotive and sensory competence to attain
lethal proximity. Extinction does not necessarily occur, however. A large
number of 'butterfly scenarios' can be constructed. As an example, the
carnivore's population may be limited by a fortuitous new factor, allowing
sufficient herbivores to survive through the random fortune of zero predator proximity to
maintain viability. -- Don

Nothing against butterfly scenarios, but do you really think a butterfly scenario can stay stable for 80 million years ( ~ the length of the Cretaceous)? I don't think it'd last 800 years, and certainly not 8000.

DM -- As for why sauropods are so big in the first place, that may
have any number of reasons. A prime candidate is the fact that the bigger you
are, the longer you can afford fermenting food in your gut, which in turn means
that you can live off poor-quality food (such as conifer needles). If you're
just big enough, you have an unlimited food source and no competition.

........... True enough, at least in theory, and as far as I can tell.
But the laws of probability mandate that 'selective vectors' are additive, just
as events are multiplicative! Assuming that "reasons" have equal
value, two reasons to get big are more likely to result in bigness than one. In
the case of inequality, you must have the knowledge and data to determine a
level of significance before discarding one in favor of another. In reality,
you may need several vectors to occur, even occurring in the proper sequence,
for directional selection to be feasible. -- DO.

Here again you predict directional selection. But there was no directional selection, see above.

While I am at it, I would like to digress a little and point
out that while size creates relative efficiencies in resource utilization, at
some point the absolute quantity of food that must be gathered is prohibitive. Heh. I still say you should go out and gather some pine
needles; say, 400 kgs? There are problems that occur... -- DO.

Doesn't strike me as more difficult than gathering 400 kg of grass, or ferns or whatever.