Re: Fw: late night thoughts: misunderstand what?

[don ohmes <d_ohmes@yahoo.com>]

Total resolution will have to wait, I suppose, as I got other stuff to do. 
Maybe a consensus on data, to start.

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?"



......... I understood you earlier as saying that _average_ bodysize had not
changed through time. 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. 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, and that the very largest known are actually from 
the Cretaceous. Has this changed? Would you name and reference the Late 
Triassic specimen that is equal in size to Argentinosaurus , a name picked more 
or less at random from wikipedia? How big is the earliest known sauropod?

Don


----- Original Message ----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Monday, June 18, 2007 8:29:10 AM
Subject: Re: Fw: late night thoughts: misunderstand what?

> I think we are assuming different margins of error. My assumptions are 
> quite large. It boils down to the probability of a given individual 
> organism being both preserved and found, something that varies according 
> to lifestyle and environment. I think that combined probability for 
> terrestrial vertebrates is very, very, very low. Finding one individual in 
> a given location indicates a long presence on the planet and says little 
> about real geographical distribution.

Are you saying your hypothesis is not testable?

I hope you aren't.

......... I am not. -- DO.

> Our perspective on evolution is evidently very different. I don't think 
> that the end theropod being the biggest, and the end sauropod being the 
> most armored, and quite large, does anything to falsify the notion of a 
> prey/predator size race.

But that's not the case. Armor has AFAIK not been found on anything bigger 
than *Isisaurus*, which was bigger than *Opisthocoelicaudia*, 
*Nemegtosaurus*, *Quaesitosaurus*, and at least most of *Alamosaurus*. 
Furthermore, it lived in India in the absence of any known extra-large 
theropods, and it's rather average for Jurassic sauropod measures. 
*Puertasaurus* is huge, but again lacks known extra-large theropods in its 
environment.

........... It wasn't me that claimed Alamosaurus was armored... don't know who 
it was. -- DO.

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?

......... Now we have something clearcut as opposed to verbal tennis. I 
nuderstood you earlier as saying that _average_ bodysize had not changed. 

I take that to mean that the largest and smallest sauropod in the Late Triassic 
were respectively equal to the largest and smallest sauropod in the Late 
Cretaceous. 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. I learned years ago that the largest sauropods 
known from the L. Jurassic are larger than the largest known from the L. 
Triassic. Has this changed?

> From what you (and others) say, that was the situation. That T.rex evolved 
> separately from the allosaurids seems indicative to me that the 
> evolutionary sub-strate was conducive to creating mega-predators.

Interesting, then, that there's no or almost no size increase in allosaurids 
from the Late Jurassic (*Saurophaganax*) to the beginning of the Late 
Cretaceous (*Carcharodontosaurus*, *Giganotosaurus*); and AFAIK the one or 
two later known allosaurids were smaller again.

> Why would I conclude that sauropods weren't a part of that?

Because they exhibit a complete lack of any trend towards increasing body 
size.
 You mean average body size, right? 

> Where's the beef?

The slaying of a beautiful hypothesis by an ugly fact.