Re: Late night thoughts: Pathetica and Interspersal

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message ----- 
From: "Tim Williams" <twilliams_alpha@hotmail.com>
Sent: Thursday, June 21, 2007 4:08 AM

> > > 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.
> >
> > No, not that either. I said that after a drastic increase in the size 
> > _range_, into both directions, with -- in sum -- _no trend_, the smallest 
> > ones (like *Anchisaurus*) died out, and the bigger ones kept diversifying, 
> > though neither the minimum nor the maximum size changed much from the MJ 
> > onwards.
>
> I read your response a few times, and I still can't figure out how my 
> response is different to your response.  This is a distinction without a 
> difference, surely.

Easy: you said there was "a dramatic increase in size that occurred early in 
their evolution (from _Anchisaurus_-sized to _Isanosaurus_-sized and 
beyond"; I said there was no such increase, only diversification. I didn't 
mention that *Anchisaurus* comes out as the result of a dwarfing event; the 
first sauropod is reconstructed as larger. The same, incidentally, holds 
even for *Saturnalia* and the first sauropodomorph.

I do agree that the maximum size didn't get pushed much after the Middle 
Jurassic, except by *Amphicoelias fragillimus* (which is not in my sample, 
but then neither are any footprints).