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Re: Gorgosaurus

From: ashwortb@lhl.lib.mo.us (William Ashworth)
 >From recent listmail I see that Gorgosaurus libratus seems to be preferred
 > now to Albertosaurus libratus.  How did this come about--I obviously missed
 > it? ...

There are two aspects to this.  First, it turned out that
_Albertosaurus_ as broadly defined (including _libratus_) is
almost certainly paraphyletic.  Since phylogenetic taxonomy
rejects paraphyletic taxa, this requires the rejection of
the boradly defined _Albertosaurus_.  For those that prefer
evolutionary taxonomy, this is insufficient reason to split
the two species into seperate genera.

Secondly, it has been claimed that _libratus_ differs as much
from the type species of _Albertosaurus_ as _Daspletosaurus_
does from _Tyrannosaurus_.  If this is so, then this suggest that
either the two latter genera should be merged or that _Gorgosaurus_
should be split from _Albertosaurus_.  (Though, personally, I would
like to see a published analysis of this issue before making up
my mind - anybody have a good literature reference on the matter???)

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.