Re: Pterosaur size (Was: Great in the air, not so good underwater)

[Tim Williams <twilliams_alpha@hotmail.com>]

Andreas Johansson wrote:

> > ------Interesting.  The very largest pterosaurs were present at the very 
> > end
> > of the Cretaceous, so apparently the rule doesn't hold for them.
>
> Doesn't seem true for dinosaurs either - the biggest theropods, the biggest 
> ornithischians, and most of the contenders for biggest sauropod, are 
> Cretaceous.

Hmmm... but are the contenders for biggest sauropods from the *end* of the 
Cretaceous?  There were some impressively-sized sauropods in the Campanian 
and Maastrichtian (_Pelligrinisaurus_ was pretty big, and 
_Bruhathkayosaurus_ was enormous - IF it's a sauropod).  However, most of 
the 'biggest' sauropods are from the Upper Jurassic or Lower Cretaceous.  
Carrano (2005) actually found a trend of decreasing body size among 
sauropods in the later Cretaceous, largely owing to the success of small 
titanosaurs, like saltasaurines.  Even thought most sauropod lineages 
achieved huge body sizes throughout their evolution, they did not usually 
maintain this size: "smaller sauropods tend to be the end points of their 
respective lineages."

As for theropods, I'm not so sure that the 'biggest' predominated at the end 
of the Cretaceous (in other words, tyrannosaurs).  There were also some 
'big' theropods in the Late Jurassic (e.g., _Saurophaganax_), and the rest 
of the Cretaceous (e.g., certain carcharodontosaurids and spinosaurids).

For ornithischians, the largest specimens do tend to pile up in the later 
Cretaceous.  There were some pretty hefty hadrosaurs around at this time, as 
well as ceratopsids.

This thread is veering dangerously close to "Cope's Rule", whereby lineages 
(allegedly) get larger over time.  The evidence for Cope's Rule is ambiguous 
at best.  While it might be possible to identify lineages that did get 
larger over time, there are those that clearly did not, and even got smaller 
(like sauropods).

Cheers

Tim

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