Re: was: Gigantism in Sauropods

[Don Ohmes <d_ohmes@yahoo.com>]

On 2/11/2011 10:09 AM, Raptorial Talon wrote:

> OK, let's think about this.

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

> 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?

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.

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.

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

> If the adults were just walking meat storehouses
> > waiting to die the next time a predator wandered through the area,

Given that you started w/ a critical error, I merely sampled the wall of 
text, and immediately am forced to ask -- who advanced that simplistic 
and easily rebutted idea? Is this yet another implied strawman?

> > >  Could you clarify exactly who "we" is?

> 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. Hence "we," those who consider such matters.

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.

> Belabored though it may be, this is not pirates-and-ninjas stuff.

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.

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

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_.

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

> the most conservative and
> parsimonious course of action is to keep our speculation constrained
> by real data from modern analogues

Now you claim parsimony.

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. Which you have not done -- circular references to the 
completeness of the data set on present-day behaviors, and pleas that 
"...it is the best we have..." do not suffice.

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

Nothing new or complicated, various claims to the contrary.

> theropods did not routinely kill
> proportionately giant sauropods,

Wow. Did I say that? Again? Uh, no...

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?