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Carcharodontosaurid Ancestors (was: When carnivores kill other carnivores...)



On 3/11/06, Cliff Green <dinonaut@emerytelcom.net> wrote:
> Mike Keesey wrote:
>
> > On a side note, I've sometimes idly wondered whether _Allosaurus_
> > might be paraphyletic with regard to carcharodontosaurids, including
> > _Acrocanthosaurus_--it's certainly a common enough genus to have left
> > Cretaceous descendants. That said, I have absolutely no morphological
> > basis for this idea.
>
>     I thought Acrocanthosaurs and Carcharodontosaurs were considered
> Allosaurus decendants. Has that opinion shifted recently?

I've never actually seen that opinion anywhere.

For that to be shown, there would have to be a cladistic analysis
showing at least one _Allosaurus_ species as sharing more recent
ancestry with carcharodontosaurids than with other _Allosaurus_
species. I don't think I've ever seen a cladistic analysis using more
than one species of _Allosaurus_. (There are probably only two
well-known species, and one is as-yet-unnamed.)

Also, a lot of researchers seem to be using monophyletic genera, so if
that result were found, it would probably involve removing some
species from _Allosaurus_, effectively making _Allosaurus_ an outgroup
to carcharodontosaurids, not an ancestor. (I think monophyletic genera
are a fairly untenable idea, at least if you're going to require every
species to be in a genus--it could be solved by allowing species to be
assigned to any type of clade, genus or not, [e.g. _Allosauroidea
tendagurensis_] but now I'm getting into an entirely different
argument....)

IIRC (and I could be wrong), some analyses actually place _Sinraptor_
and _Yangchuanosaurus_ closer to carcharodontosaurids than
allosaurids, so I suppose they might be equally good ancestor
candidates. If only there were more deposits from the Berriasian....
--
Mike Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com