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Re: was: Gigantism in Sauropods



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?