Late night thoughts: Pathetica and Irony

[don ohmes <d_ohmes@yahoo.com>]

This is getting ludicrous.



1). Your "hypothesis" is, you state, that for predator driven size selection
(size race) to be shown within a given population, minimum size must increase 
as well
as maximum size. That is absolutely incorrect within groups composed of more 
than one species. Barring sample bias or data error, if minimum size and 
maximum size
_both_ increase, it is symptomatic of a selective regime in place that is 
affecting all
animals within the group, such as an environmental factor or an illusory 
uber-factor like Cope's Rule. Relative to minimum size, it is the exact 
opposite pattern expected from a predator-driven
size trend in a multiple species population. When predator pressure occurs on a 
multi-species group of the size
(species-wise) and time-frames considered here, some elements inevitably find
refugia from the pressure, whether the refugia is environmental, geographical, 
or biological.
Adaptation to refugia frequently involves size change, including size decrease.
Your statements are tantamount to insisting that in order for predation to
affect size, predation and ONLY predation can be operating, and the predation
pressure must affect all the potential prey organisms equally across the board.
This is simplistic, and ignores the fact that probability, and therefore
selective vectors, are additive. These standards of definition that you imply 
are stringent enough to
eliminate the useful, valid, and BEDROCK concept of prey/predator size
selection from evolutionary/ecological theory.



2). Hone's study, that you so flippantly cite, was testing Cope's Rule. OF
COURSE MINIMUM SIZES HAD TO INCREASE FOR A POSITIVE RESULT. Perhaps Hone will
weigh in on whether he thinks predator pressure had anything to do with the
size of the mega-sauropods... or whether sauropod size affected the size of any
of the maximal meat-eating theropods. 




3). Patterns found by Carrano evidently support the thesis of predator pressure 
and perhaps even
a 'predators won' picture (I hasten to add I do not know of him advancing that 
idea or expressing any opinion on it). To paraphrase, the big sauropods 
'sputtered out at
the end', and size decrease in sauropods 'signaled the end of the lineage'. 
Note the post-Mid-Jurassic giants that just disappeared. A 'scientific' skeptic 
may argue the neutrality of the evidence, the fossil record
clearly does not falsify the concept of predator-driven size selection among
sauropods. Given the vagaries of preservation, I am not sure it could confirm 
or deny in this case.



4). I thought you would retract, but evidently you stand by this statement;



DM -- "And then there's, again, the fact that neither minimum nor

maximum nor average sauropod (or even sauropodomorph) size increased

across the Mesozoic. Your hypothesis says they did grow bigger, the

fossil record says they didn't, your hypothesis loses. Am I missing

something?" 


What you are missing with me at this point is credibility. First, it is not my 
hypothesis; this is the first time I have heard anyone with any knowledge of 
evolutionary theory dismiss the idea that the mega-sauropods weren't driven at 
least to some degree by predation. 'Predators won' has also been advanced many 
times, I would bet. It has been, in fact, consensus that they "got so big to 
avoid predation, so they could be invulnerable" for over a 100 years, right? MY 
HYPOTHESIS IS THAT THERE ARE HUNTING STRATEGIES AVAILABLE TO TALL BIPEDS WITH 
LARGE JAWS, AND VULNERABILITIES INHERENT TO LONG SKINNY NECKS, THAT ALLOW ONE 
TO SPECULATE, AMONG _OTHER THINGS_, THAT 'PREDATORS WON'. Second, the statement 
that maximum sauropod size didn't increase "across the Mesozoic" is so bizarre 
I strongly suspect you are pranking me. Like "assisted running", a couple of 
minutes on Google will tell _anybody_ all they need to know. 

Sum-- If you think there are Triassic giants out there, go find one. As to 
average size, it is not relevant above the level of species, due to the 
confounding effects of refugia. Not to mention being so subject to sample and 
measurement error as to be laughable. Minimum size has meaning, _perhaps_, but 
not the one you ascribe to it. You said "let's end this one here". That is fine 
with me. I want to spend my time on things relevant to hunting strategies, and 
important stuff like how long could a sauropod hold it's breath, and I much 
prefer chess to tennis anyway.. If you reply to this post, DO NOT DELETE 
ANYTHING. And don't intersperse, please. Clear a space above or below, and 
leave my words intact so people HAVE to know what I said, and I don't have to 
say it again. Thank you! -- Don



----- Original Message ----

From: David Marjanovic <david.marjanovic@gmx.at>

To: DML <dinosaur@usc.edu>

Sent: Monday, June 18, 2007 5:15:17 PM

Subject: Re: Fw: late night thoughts: misunderstand what?



> ......... I understood you earlier as saying that _average_ bodysize had 

> not

> changed through time.



Rather, there is no trend in sauropod body size.



> The above statement means that the maximal sauropods are equal through 

> time,

> a much more radical statement. In other words, at any timeslice in the 

> total

> time of their existence, the largest sauropods known from that

> timeslice are equal to those found in any other timeslice.



Not necessarily -- I'm just saying that there's no trend in sauropod body 

size.



> I learned years ago that the largest sauropods known from the L. Jurassic

> are larger than the largest known from the L. Triassic, whether measured

> by height at the shoulder, or weight,



Correct, but you must take phylogeny into account. (I said science is a lot 

of work!) The Early Jurassic *Gongxianosaurus* already reached 15 m in 

length, more than all other Early Jurassic and many Middle Jurassic 

sauropods, but it is very basal, more so than the Late Triassic 

*Antetonitrus* and *Isanosaurus* for example. Likewise, there's a 1 m long 

humerus from the end-Triassic of Thailand attributed to an adult 

*Isanosaurus*; that hints at a 15 m long animal, too.



> and that the very largest known are actually from the Cretaceous. Has this


> changed?



Well... *Amphicoelias fragillimus*, from the Late Jurassic, is a size class 

of its own. Then comes the trackmaker of *Breviparopus*, estimated to be 48 

m long last time I checked, and Middle Jurassic in age. Next are 

*Argentinosaurus* and *Paralititan* from the "middle" Cretaceous
together 

with *Turiasaurus* from the Late Jurassic and *Puertasaurus*. The 

distribution of giants and supergiants among the sauropods looks rather 

chaotic from the Middle Jurassic onwards.



> How big is the earliest known sauropod?



No matter which one that is (it's not easy to correlate between continents), 

it's a lot bigger than *Anchisaurus*, the smallest known sauropod, which is 

a lot younger. :-) Importantly, the reconstructed size of the _really_ first 

sauropod is also above that of *Anchisaurus*. Some sauropods got smaller, 

not larger.