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).