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Re: was: Gigantism in Sauropods



Big ol' post.

> I have been doing just that, using an explicit model of incremental 
> evolution, and concrete data. You know -- >height, weight, tooth morphology 
> -- avoiding hand-waving or special pleadings as much as I can.

You've been arguing that prey/predator size ratios in extant forms are
not a valid null hypothesis relative to extinct ones, period -
because, you claim, they are merely a matter of opinion, and hence
that modern observations cannot constrain behavior in extinct animals.
Not these ones anyway. You even argued that it was not "scientific,"
and suggested that your notion of "tactical capacity" was superior for
understanding the evolutionary patterns we observe for the taxa in
question. I disagree. The constraints from observations of living
behavior may not be as concrete as for biomechanics, but they do exist
and they are relevant and informative with regards to assessing the
probability of one behavior over an alternative behavior.
Specifically, I've suggested that size was an effective deterrent to
predation in sauropods, and hence that big sauropods were largely free
from worry about predators, rare exceptions aside; but also that size
was not driven primarily by predation pressures. Further, I question
the informativeness of the blow-by-blow approach, especially in the
context of modern observations.

If there's been any miscommunication, that's unfortunate and I'm glad
to rectify it.


>I also try hard to focus on parsimony, and pay close >attention to precision 
>and concision in thought and >language. Especially when self-editing...

What's that supposed to mean? I do the same thing. I'm sure most
everyone with interest enough to post to this list can say the same.


> Wrong. Heritable size, and higher reproductive success of large individuals 
> is the "*cause*" of a predator-driven size increase in both prey and
predator, by evolutionary logic.

So the process is driven by predators, but caused by something else?
Is there some technical difference between "driven by" and "caused by"
that I should be aware of?

No predators = no higher reproductive success associated with
avoidance of predation. Based on other factors, sure, but not on
predation if there aren't any predators. Predation is therefore the
root cause, the external selective pressure required for the process
to be directional; heritability and reproductive success are the
*mechanisms* by which evolution is achieved, not the forces that cause
modification of the genetic makeup of the population. I.e., it's
predation that actually removes genetic material from the population
and thus determines, for its part, which sets of genetic material are
passed on. The devoured ones don't t get to reproduce that year . . .


> The evolutionary mechanisms you describe above (predator preference for large 
> individuals w/in the cohort) lead by evolutionary logic to predator-driven 
> size DECREASE, at least in prey. This a fundamental error.

What? Look at that again:

"If gigantism in sauropods was primarily a *response* to predation
pressure by theropods, then theropod predation *upon large
individuals* is the *cause* of sauropod gigantism, correct?"

(Setting up a premise for evaluation.)

"Hence, I would expect to see proportionately large theropods
threatening proportionately small/medium sauropods before the
evolution of really super-huge sauropods relying on their quadropedal
posture to permit them to outstrip predators limited to bipedal size
constraints. If predation was a primary driver rather than a secondary
component, that is."

(If the premise were true, I might expect to see this, given that size
is a selective advantage which allows slow, can't-run-away sauropods
to achieve a defense, as described elsewhere in that post and others.)

"If hunting sauropods were such an incredibly metabolically
advantageous capability, I would not
expect to see these couple-hundred-kilogram predators trying to cope
with 3- to 20-ton adult sauropods, I would expect to see
two-to-four-ton bruisers like the bigger allosaurs and torvosaurs."

(I argue the premise which was set up rhetorically is not actually
supported by observations in the fossil record.)

"Sauropod gigantism simply is not best-explained
singularly by anything - but especially not by predator deterrence,"

(Therefore, other causes must be sought.)

A little reading-comprehension failure? The whole point of my post was
to illustrate ways in which *actual fossil observations* do not
support the idea that sauropod gigantism was driven primarily by
theropods. So when you say "Predator preference for large individuals
w/in the cohort lead(s) by evolutionary logic to predator-driven size
DECREASE in prey, (hence that is) a fundamental error," yeah, that's
the idea. It's an angle I hadn't considered - and it sort of misses my
point - but unless I've mistaken you, I'm glad you at least agree with
me that there is no support for predators preferring the largest
individuals.

That was just a setup to make a point.I don't know how you missed the
spiel about juveniles being preferable over adults or about how high
growth rates strongly imply size was a significant deterrent, but
those were supposed to underscore just how improbable a preference for
large individuals would have been.


> BTW -- The advantage of size in digesting plant >nutrients is best 
> characterized as an enabler, not a driver, due to complexities encountered 
> when trying to >create an incremental predator-free scenario that transitions 
> from "easy" to "hard" fodder.

. . . if low-quality fodder is the only fodder available, whether due
to the local soil conditions or due to competition with rivals that
are superior at utilizing higher-quality fodder, then any herbivore
forced to exist in that ecosystem with poor fodder as its available
food base is under strong selective pressure to make good use of that
resource, is it not? If it can't use its only recourse at the present
time, then it must adapt or die. Some examples come to mind: koalas
evolved complex stomachs and lethargic but territorial behavior to
make use of a low-quality food source. Elephants appear to benefit
from the digestive efficiency of animals their size in an environment
where ruminants, which can't reach those sizes because of
physiological limitations, are otherwise the prime competitors.
Similarly for horses in high-latitude environs, albeit much less
extreme and for somewhat different reasons.

I know that's a simple version of the scenario, but it certainly does
seem to me that digestive efficiency is a potential advantage which
stands to be acted upon by natural selection, predator-free or
otherwise. If size is the "path of least resistance" by which an
organism of whatever morphology and physiology can achieve said
efficiency, then that too would be operated upon as a correlated
character. I suspect, though, that I'm missing some key element of
your point here; perhaps you need to be less concise about it so the
relevant portions don't get left out.


>No such complexity arises in predator-only
> scenarios. Parsimony counts.

Further, maybe explaining your argument in-context would be more
effective at communicating it to me than making detail-free statements
about what you've previously concluded.


> Given that you started w/ a critical error, I merely >sampled the wall of 
> text,

Let me rephrase that on your behalf with the necessary corrections:

"Given that I totally misunderstood the point of what you were saying
in the first paragraph, I decided not to investigate the rest of your
point, either."

Real smooth.

Would it be easier on your noggin if I wrote a handful of sentence
fragments per post instead of a thorough multifaceted reply - or as
you so eloquently put it, a "wall of text?"

I suppose if you're not going to bother to read most of the multiple
facets, there's not really much point. But I also really do have to
advise you to read through people's posts before dismissing them out
of hand.


>and immediately am forced to ask -- who advanced >that simplistic and easily 
>rebutted idea? Is this yet another implied strawman?

No, just an exaggeration on my part. Intended to underscore the core
elements of what I perceive(d) as the gestalt of your argument thus
far: that big theropods could, based on a blow-by-blow "tactical"
account, if not easily then fairly routinely kill rather large
sauropods, to the point of being a significant selective pressure upon
them (thus triggering/perpetuating/whatever an evolutionary arms race
with them).

I guess sarcasm isn't the only thing that doesn't work so well on the
internet. Even obvious exaggeration for the sake of effect doesn't
carry through.


> I suspected I might be included in that "we". I suggest you use "I expect" 
> instead of "we expect" -- unless you are referencing physical law.

Thanks, and I'll just continue using "we" however I see fit. Like when
I'm referring to people other than myself, for instance, even if their
involvement is currently hypothetical.

Also, a little lesson in reading comprehension:

"Certainly: those who participate in making observations of the
evidence. I.e., *IF* the evidence is there, anyone should be able to
see it; and *IF* the logic is there, anyone should be able to follow
it, *BARRING* communication problems or *LIMITS* on the evidence it
follows from."

I fail to see how this does not apply to you. I left plenty of room
for reasonable disagreement to stem from mundane observations about
the nature of evidence, and the nature of human communication of that
evidence. I didn't say the evidence for my line of debate actually
existed absolutely and that you must thus acknowledge it. Nowhere in
those couple sentences did I claim that my logic thus far has been
even so much as legitimate, or that you are inherently party to it. It
was simply a statement that if there is only one reality, those who
observe it should come to only one conclusion about its nature, if -
wait, wait - *IF* they have all the pertinent knowledge about that
reality. Those factors apply to me, and they apply to you. That means
a collective pronoun applies. Deal with it.


> As an aside -- writing the phrase "pirates-and-ninjas stuff" does not 
> discredit an analysis of the theoretical strengths and vulnerabilities of  
> the sauropod/theropod couplet on varying substrates, or change the value of
such analysis generally.

No, but the theoretical - well, more properly *hypothetical* when
taken together - strengths and vulnerabilities are speculative. Not
biomechanically, necessarily, but instead because the biomechanics had
to be expressed through behavior, which was constrained by ecology as
well as morphology. This blow-by-blow method is implicitly trying to
dictate behavior from almost purely biomechanical observations, yet
the diverse behavioral complexity of modern animals of the same or
similar morphology *strongly* argues that specific behavior cannot be
deduced from bones alone, regardless of what scenario you imagine the
living animal in. (Accounts of coevolution derived from said scenarios
thus suffer in tandem, because the evolution is based on what the
animals actually did with their actual behavior, not what they were
potentially capable of doing.) Understanding the complexity of the
ancient ecosystem *as it really was* is thus only marginally served by
such observations. I'm all for including speculation in scientific
discourse when data is limited, so long as it's just a field for
discussing possible directions for research, but I think the degree of
insistence you display about this far exceeds such uses.

So a coyote is very similar to a wolf except for size, yet their real
behavior is very different under virtually all circumstances. Lions
and tigers are all but indistinguishable skeletally but have
distinctly different life strategies and prey-capture behaviors.
Humpbacks are quite similar to other rorquals physically, but their
breeding habits are unique. We have no a priori reason to assume that
theropods even of similar morphologies were not at least somewhat as
diverse, so these descriptions of "they all must have done this
because they were physically capable of it and it was a big metabolic
payoff" are simplistic, at least as the versions I've seen rendered
thus far go.

> Also -- an analysis of tactical capacity is NOT the same as an analysis of 
> probable behavior, even though >it sets parameters on POSSIBLE behavior.

Hm. Funny you should mention that.

Let's take a little trip down memory lane.

"Why would the theropod not simply let go, and wait a bit."

Huh. Why, indeed? After all, isn't it more *likely* the theropod would
let go and wait?

Oh wait, that's not a statement of what it's possible for a theropod
to do, it's a statement of whether or not a behavior is *probable.*

"Still sounds less dangerous and less likely than falling while
running fulltilt after smaller faster prey. Especially given that
simply harassing a giant sauropod for 2 or 3 days might get you a huge
happy meal w/out a bite fired, so to speak."

"less likely than . . . running fulltilt." So running fulltilt is a
possibility, but it is less probable.

Harassing a giant sauropod can procure food, you say? Especially since
pursuing smaller prey isn't worth my while? Well, I guess I should
specifically target sauropods with that specific behavior. Not because
I'm physically constrained to do the one and not the other, but
because one is a better option!

Gee, wherever could I have gotten the notion that you were discussing
probability instead of sticking strictly to mechanical possibility?

Also, it's ecological reasoning derived originally from observation of
behavior in living organisms. Nice.

Yet I think I know exactly why you did this in that first reply to me.
Consider an example. A bit of an extreme one, intended to illustrate a
point: "Amphicyonids were biomechanically capable of living in
eusocial colonies, and biomechanically capable of taking down
indricotheres by swarming them with sheer weight of numbers."
Technically true. Throw enough beardogs at the target, and eventually
it'll go down. But that doesn't make one damn lick of sense
behaviorally or ecologically, so *why talk about it?* The range of
physical possibility is so much vastly broader than the range of
actual behavior that postulating specific behaviors (which you did,
see above, no denying it) is not notably informative. If you're really
interested in delineating physical limitations, then talk about jaw
power or stride length or neck flexibility or other stuff that's
actually quantifiable.

Yes, yes, I know you do that in the course of devising a tactical
scenario, but devising said is an *unnecessary step* that doesn't
really add much in the way of useful data. Your swamp versus open
ground comparison is interesting and could have real value for
understanding a given ecosystem, so I do see some value here. The
specific attributions of behavior based on capability - like
"Especially given that simply harassing a giant sauropod for 2 or 3
days might get you a huge happy meal w/out a bite fired, so to speak"
- I think are much weaker and far harder to defend except as loose
speculation.

So I know why you went into statements of specific probable behaviors.
It's because that's what we really want to know. Physical parameters
are all well and good because they give us hard data, so that's fine.
Blow-by-blow accounts, on the other hand, don't add a whole lot to our
knowledge, since possibility is so open-ended once the biomechanics
are understood and the range of physical possibilities is too enormous
to draw solid conclusions about - unless we bring ecology and
evolutionary reasoning into play. And even then, it's kinda vague. The
real meat lies in specific behaviors. We all wish we could see them,
we all want to delimit the options to get as close as possible to
understanding what they might really have been, and so on. Hence,
slipping into that mode of thought can easily be forgiven, I should
think.

To be fair, you were indeed trying to use ecological and evolutionary
reasoning in some of your replies here, but I think my point is that
various lines of evidence (r-strategy, growth rates, risk-reward,
modern analogues) render discussion of tactical capability pretty much
irrelevant. The fact that you handwave away basic ecological
principles widely observed in virtually every macroscopic biotic
system on Earth does not logically counter them.


> I include an example, due to the evident persistent confusion on the point 
> immediately above -- airplane pilots have the tactical capability to 
> deliberately crash their planes. This gives them the tactical capacity to
> kill large numbers of people.
>
> On average, they _rarely do_. Yet these rare events dramatically affect their 
> "ecological niche". In >assessing the probabilities relative to an individual 
> pilot, the group average can be _highly uninformative_.

I'll give you that there seems to be some communication problems at
work here, but I'm also forced to say that this is a terribly flawed
analogy. As any comparison of evolutionary ecology to deliberate
intelligent actions must be, ultimately. I know what you're trying to
say, but where I disagree is the notion of "dramatically affect(ing)
their ecological niche." I don't think the purported capabilities of
large theropods had a dramatic effect on their niche vis-a-vis giant
sauropods, because it seems to me that predation upon giant sauropods
would have been so rare as to be almost wholly insignificant for the
purposes of any coevolutionary arms race. Just like I don't think the
evolution of *Loxodonta africana* has much of anything to do with lion
attacks, because they're so rare, and adult elephants (and the
populations they comprise) are well-adapted to dominating lions 99.99%
of the time. Or whatever. It's not a major point in the survival of
the species.


> The concepts apply to large animals, are historically tested and 
> well-understood.

So are the principles of animal ecology - that is an entire major
branch of science, you know - which you go on to dismiss out of hand
as irrelevant for establishing behavioral constraints on extinct
organisms.

Pot, meet Kettle.

Here, let me show you something interesting: *Plateosaurus* had
leaf-shaped teeth with blunt serrations. Modern animals with
leaf-shaped teeth with blunt serrations are observed to mainly eat
plants by cropping them with their teeth. Therefore, *Plateosaurus*
most likely engaged in the behavior of cropping and ingesting plants.
Further, it likely did not engage in the behavior of cracking bones or
hard-shelled prey, because modern animals that crack bones or
hard-shelled prey have blunter, usually flatter teeth without
serrations.

Bam. I just falsified your notion that observations of behavior in
modern organisms are irrelevant and unscientific. Uniformitarianism
applies to biology, even if clear interpretations are more elusive
than in geology.

If I were to hand a complete skeleton of a dinosaur to  computer that
could analyse biomechanics but had no other external data, it could
tell me pretty much jack squat. It wouldn't know that animals need to
ingest food to survive, it wouldn't know that they reproduce, it
wouldn't know that they routinely engage in competition, predation, or
resting, it wouldn't know how cellular growth or digestion or
thermoregulation work, or how all of the above is linked to genetics.
Guess what? Our understanding of all of that comes originally from
observations of modern organisms and the *behaviors they use to
fulfill those needs.* They are the underpinning of almost everything
we know about extinct animals.

Thus, I can say with a high degree of confidence that plateosaurs
cropped plants, that ornithomimids used speed to flee from predators,
that corythosaurs used their crests for some sort of individual and/or
species recognition, that tyrannosaur face scars come from fights over
meat, mates, or territory but not from fights over fruit, feeling
full, or for the hell of it, and that this statement:

"Ignoring tactical capacity on grounds of conjectured behavioral
limitations when evaluating the possible evolutionary paths by which
this coeval morphological couplet came into full flower is neither
useful nor "scientific"."

. . . is pretty much BS as far as I can tell. Maybe I've missed
something, but that's where I stand currently.

Tactical capacity =/= actual behavior. Observations of living animals
= actual behavior. Observations of living animals = strong source of
evidence regarding past animals. Hence, observations of actual
behavior = strong evidence of behavior in past animals. With caveats,
of course. All techniques have their limits.

> Now you claim parsimony.

If you had actually bothered to read my full post (which I recall by
your own admission you did not), maybe this wouldn't have come as a
surprise.


> Sorry, fail on that -- also, you must justify the contention that the 
> behavior of Mesozoic giants can be >divined by watching the behavior of bugs 
> and foxes.

If the patterns that govern bugs and foxes are the same as those
governing whales and pelicans and Gila monsters and horseshoe crabs
and ever and anon, why the hell would we *ignore* them? Sure, some
patterns apply to more limited subsets than others, but if they apply
consistently and across diverse sizes, habitats, morphotypes, and
taxa, then yes, you're damn right we should take them seriously when
it comes to extinct organisms. Your notion that Mesozoic giants were
special and somehow not subject to observable evo-ecological rules is
the only special pleading going on here.


"Which you have not done -- circular references to the
> completeness of the data set on present-day behaviors,

OK, I don't understand that on a grammatical level.

"and pleas that "...it > is the best we have..." do not suffice."

All we have of dinosaurs are bones, eggs, nests, footprints, and a
rare few other traces. Understanding how skeletons are used *must* be
done in the context of observing modern animals. There is no other
source of information for how living organisms use(d) living parts.
Understanding how nests are formed or how eggs are arranged is
something that *must* be derived from observations of living
organisms, because that is the only way to see the the workings of the
action which produces the feature. Seeing how footprints or burrows
are formed relative to different substrates can be replicated in a lab
to some degree, but benefits enormously from being informed by
observation of the makers in question. It is NOT SPECIAL PLEADING to
assert that understanding behavior in extinct animals is *also*
something that *requires* observations of behavior in living ones.
This is one of the fundamental constraints on possible past behavior,
along with biomechanics.

We're trying to understand forms of behavior which we know to have
existed, but otherwise know very little about. You champion the use of
biomechanics as a constraint on this, and that is right and proper.
Then you seem to turn around and say that an additional form of
constraint, one which allows us to be even more precise about the
range of likelihoods, is actually irrelevant and need not be taken
seriously. Modern behavior is what allows us to easily say that
theropods didn't routinely walk in place for hours at a time, even
though they were biomechanically able to do so. Modern ecology is what
allows us to say that receiving an open wound presented a serious risk
of infection, then as now, and to say that ceratosaurs didn't make
thousand-kilometer migrations every year, even though their legs in
and of themselves would have been able to do so. I am baffled at what
appears to be your (admittedly inconsistent) resistance to the idea of
basic known factors like reproductive strategy, growth rates, trophic
functions, and other variables *understood entirely through study of
modern organisms* having a serious role to play in the interpretation
of the behavior of these animals.


> Extant terrestrial top herbivore life-histories are instructive, though.

Oh, now you agree. Suddenly "no best-we-have!" becomes "yeah, sure,
there's stuff to be learned from this."

> Only the largest individuals are RELATIVELY safe from predators, hence size 
> grants them reproductive advantage. Size is heritable. In hard times,
> however, they can in principle ALL be taken down and eaten.

Only if hard times are common, and if "in principle" is actually "in
practice," would we expect to see notable evolutionary signal from
this.

Also, it's totally false. Adult rhinos are not taken down by hunting
dogs or cheetahs during lean times, nor are adult African elephants
taken by leopards or crocs in rainforests where those are the apex
predators because others are absent. Adult Asian elephants are not
taken down by tigers, leopards, wolves, or dholes. Adult bison are not
taken by cougars, and in the last glacial period adult steppe mammoths
- nearly twice the mass of modern African elephants - were most likely
not threatened by cave lions, which were only 20% bigger than modern
ones. I can't see 20-ton adult indricotheres going down to solitary
half-ton hyaenodonts, either. Et cetera. Size, in a healthy adult,
really does prohibit at least predators of some morphologies and
lifestyles from making the kill. Full stop.

At best, a single large predator species in a given ecosystem is able,
rarely, to take the largest or otherwise most difficult prey. This is
not necessarily true, however; some ecosystems can have largest
predators which are incapable of taking the largest prey, while others
can have predators which rely *primarily* upon the largest prey
(cougars+vicunas, jaguars+capybaras, and wolves+moose are specific
instances in some ecosystems that spring to mind. Of course, even in
those cases, juveniles are targeted frequently as well, but the
attacks on the big individuals are still common and noteworthy).
There's nothing in ecological understanding to *preclude* either
extreme, so we have to be careful about the null hypothesis we run
with.


>> theropods did not routinely kill
>> proportionately giant sauropods,
>
> Wow. Did I say that? Again? Uh, no...

Ahem.

"Still sounds less dangerous and less likely than falling while
running fulltilt after smaller faster prey. Especially given that
simply harassing a giant sauropod for 2 or 3 days might get you a huge
happy meal w/out a bite fired, so to speak."

Certainly made it *sound* easy enough to be routine.


> As I have been repeatedly making clear since I first advanced the idea 
> _onlist_ that substrate-driven >changes in the balance of power were 
> inevitable between giant sauropods and theropods, and had >serious 
> evolutionary implications relative to size (among other things) -- when was 
> that? 2005 or 2006?

I only signed on in 2008, so beats me.



As a final aside, I'll tone down my snark if you tone down yours. Your
responses seemed to get more dismissive and peevish successively, and
while I kept my initial responses clean, you came back (after
apparently not even really reading the last post) and piled on even
harder. That pushed me past my limits for civil discourse in this
post, but I'm willing to let it drop if you ease up in future replies.