Re: Allosaurus fragilis vs. "Creosaurus" atrox

[twilliams@canr1.cag.uconn.edu]

> Is there any simple way of telling apart _Allosaurus fragilis_ and
> "Creosaurus" atrox?  Bakker seems to have shown that these two species are in
> distinct genera (whether Creosaurus is correct or atrox needs a new genus is
> beyond me).  However, most publications label pictures of these allosaurs as
> _A. fragilis_, or, simply, _Allosaurus_. 

Bakker has not shown that these two species are distinct genera - at 
least not in any scientific publication.  The name "Madsenius" was 
proposed for certain _Allosaurus_ specimens which he considered 
distinct from "true" _Allosaurus_.   I've also heard that another 
_Allosaurus_ specimen has been tagged as a new genus by Bakker, with 
the name "Wyomingraptor" proposed for this one.    

Check out David Smith's recent paper in the _Journal of Vertebrate 
Paleontology._ :

Smith, D. K., 1998. "A morphometric analysis of _Allosaurus_," J. 
Vert. Paleont. 18(1): 126-142.

There are two species of Morrison Formation _Allosaurus_, according to this 
study: _Allosaurus fragilis_ and _A. maximus_ (formerly 
_Saurophaganax maximus_).  As for "_Allosaurus/Creosaurus atrox_", the features 
used to distinguish this species from _A. fragilis_ can be attributed 
to intraspecific variation within the species _A. fragilis_.  
Strongly developed lacrimal horns, for example, represent just one 
end of the allometric spectrum; the size and shape of the lacrimal crest 
exhibits a lot of variation within the species.