Re: Tyrant taxonomy (was RE: Big Bakker article in June Discovery Mag)

[Dinogeorge@aol.com]

In a message dated 5/2/03 4:57:07 AM Pacific Daylight Time, 
tholtz@geol.umd.edu writes:

<< Okay, in reality, we can say that:
 a) Many, although by no means all, paleontologists working with large
 theropods consider _Gorgosaurus libratus_ to be distinct from _Albertosaurus
 sarcophagus_.
 b) Futhermore, everyone now (as far as I know) agrees that _Gorgosaurus
 libratus_ (or _Albertosaurus libratus_, or the Judithian specimens of
 _Albertosaurus sarcophagus_ if you really want to lump) is distinct from
 _Daspletosaurus torosus_.
 
 As an aside (and especially for newer folks on the list), there does not
 exist such thing as a genericometer or as a fully agreed-upon metric for
 telling whether a proposed species is "valid" or not.  Really.  Truly. >>

My genericometer indicates they're too close to call separate genera. Just 
three species of the single genus Albertosaurus, which has priority:

Albertosaurus sarcophagus
Albertosaurus libratus
Albertosaurus torosus

The key character uniting these into a single genus would be the presence of 
the lacrimal horn, which doesn't occur in other tyrannosaurids, either 
Asiatic or North American. Otherwise they're very similar overall, A. torosus 
being the most different of the three species. I think some of the "new" 
tyrannosaurids whose descriptions are pending may well be yet more species of 
the genus Albertosaurus.