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Re: Allosaurus fragilis vs. "Creosaurus" atrox
> 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
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.