Re: Questions of Various Kinds

["Tim Williams" <T.Williams@cclru.randwick.unsw.edu.au>]

I'll take a punt at a few of these.  Feel free to criticise if these 
answers are way off the mark.
 
Rachel Clark wrote:

> 5) Do specimens of _Allosaurus_ suggest any kind of sexual dimorphism?

All in the eye of the beholder.  It's clear that Morrison allosaurs 
come in two morphs - gracile and robust - but there's differing 
views over whether these morphs constitute two distinct species 
or two sexes of a single, sexually dimorphic species.  In _Predatory 
Dinosaurs of the World_ Greg Paul asserts that there were two 
sympatric species, and calls the gracile allosaur _A. fragilis_ and 
the more robust species _A. atrox_ (after _Creosaurus atrox_).  The 
fact that the former is a much rarer species - it is unknown from the 
Cleveland-Lloyd Quarry - tends to support the idea of two distinct 
species.

I've also heard the view that "_A. atrox_" is a distinct genus from 
_Allosaurus_ - not yet officially named but both "_Creosaurus_" and 
"_Madsenius_" have been proposed.  ("_Madsenius_" is one of Bakker's 
proposed genera; in the view of he and many others, the lectotype of 
_Creosaurus atrox_ is indeterminate therby invalidating further usage 
of the name.).
 
> 12) Is _Ornitholestes_ closely related to _Allosaurus_?

I don't believe so.  _Ornitholestes_' allosaur-like characters 
(recognised by Greg Paul - "box-like" braincase, decidedly non-
cursorial hindlimbs, etc) may be "holdovers" - _Ornitholestes_ is a 
primitive coelurosaur, so not too far removed from the group's 
divergence from the Allosauroidea.
 
> 14) Is _Albertosaurus_ the valid generic name for the species "A. libratus"?

The type species for _Albertosaurus_ (_A. sarcophagus_) is a 
fragmentary skull which some researchers believe is too poorly 
preserved to diagnose a valid genus.  This throws the referral of all 
other _Albertosaurus_ species into doubt.  Apparently the whole 
_Albertosaurus_ mess is being sorted out at the moment, and a paper 
is (reputedly) in the pipeline.