Re: Late night thoughts: Pathetica and Interspersal

[don ohmes <d_ohmes@yahoo.com>]

One final blip, and I am off to get my 2.5h of zzzz.

"Such a 
hypothesis makes a prediction that there is a correlation between increased 
body size in theropods and sauropods."

The relevant metric is theropod jaw vs neck base, relative to the skinny neck 
scenario.... 

----- Original Message ----
From: don ohmes <d_ohmes@yahoo.com>
To: twilliams_alpha@hotmail.com
Cc: dinosaur@usc.edu
Sent: Wednesday, June 20, 2007 1:54:31 AM
Subject: Re: Late night thoughts: Pathetica and Interspersal

No, it calms it. You make reasoned points, and make detailed statements about 
the record that are credible. Here's what I don't understand about the 'take'.

Lineages 1,2,3,4,... through time. Each gets big, hits an apparent overarching 
size limit, then sputters, dies. 

How does that negate predation as driver, and 'predators won" if the size limit 
is real?  L1,2,3,4 cannot demonstrate an overarching size trend under those 
conditions. I run from an enemy, get to 65 mph, get busted. then you do the 
same. Does the fact you didn't get busted at 70 mean you are not being chased? 
Or that you are not being chased by something that can go faster than 65, and 
you HAVE to get busted?

The "little" guys found refugia, possibly because large bipeds don't like soft 
ground. "I fell and I (blub, blub)..." The 'sputterers' can also be explained 
by refugia. Prolificity, fortuitous predator population decline, etc. I guess I 
should note I use refugia in the broadest sense, as opposed to the more 
classical geographical sense.

Hope that made sense. Sheesh it is late. And I have to rise at 5. I may get 
selected myself today.

Don

----- Original Message ----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu
Sent: Wednesday, June 20, 2007 1:32:59 AM
Subject: Re: Late night thoughts: Pathetica and Interspersal


Don Ohmes wrote:

>You will have further noticed that in this thread he makes claims about 
>maximum sauropod size that yield a logical conclusion; that directional 
>selection for size never occurred in the largest land animals ever to have 
>lived. So much for evolution, apparently. He says they were always all the 
>same size anyway, or possibly just appeared at full size and then decreased 
>in size,

No, David didn't say that at all.  What he said was that after a dramatic 
increase in size that occurred early in their evolution (from 
_Anchisaurus_-sized to _Isanosaurus_-sized and beyond), sauropods had 
essentially hit their maximum size by the Middle Jurassic.  In other words, 
the biggest sauropods of the mid-Jurassic were as big as the biggest 
sauropods at any point thereafter (except for maybe _Amphicoelias 
fragillimus_ of the Late Jurassic).

Further, it doesn't matter how you define "big".  Within each of the major 
sauropod lineages (diplodocoids, brachiosaurids, titanosaurs) average size 
appears to have peaked, and then gone downhill.  For example, although the 
Titanosauria produced some extremely large taxa in the later Cretaceous 
(e.g., _Argentinosaurus_, _Puertasaurus_) the average is dragged down by the 
appearance of a slew of much smaller titanosaurs (e.g., saltasaurids).  This 
is what Carrano found.  You may argue that certain sauropods got bigger as a 
defense mechanism, which might well be true.  But this argument of 
"directional selection" cannot be upheld as a general overarching theme for 
sauropod evolution.

>and that both patterns falsify predation as a factor in sauropod size, 
>which they do not.

If your hypothesis is that sauropods were driven to large body size by 
theropods (and/or vice versa), you must demonstrate a correlation.  Such a 
hypothesis makes a prediction that there is a correlation between increased 
body size in theropods and sauropods.  Thus, it can be tested.  If such a 
correlation is demonstrated (quantitatively) to exist, then we have room to 
speculate on causation.

I hope this doesn't inflame the debate any further.

Cheers

Tim

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