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

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dinogeorge@aol.com
>
> My genericometer indicates they're too close to call separate
> genera.

Fair enough.  The important point is, of course, that "genericometers" are
all calibrated to individuals: that is, there are no universally accepted
objective criteria for deciding when two individuals are different at the
"species" level or the "genus" level or what have you.  George might have a
genericometer set for very broad species or genus definitions; Bakker's is
notoriously set on a very narrow calibration.

> 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.

URK!!!  Well, yes, the horn is currently only known on these three, but
_Daspleto._ shares many additional features with _Tarbo._ and _Tyranno._
(either alone or in combination).  I can see a phylogenetic case being made
for including _Daspleto._ in _Tyrannosaurus_ (as Greg Paul did), but not
_Albertosaurus_.

> I think some of the "new"
> tyrannosaurids whose descriptions are pending may well be yet
> more species of
> the genus Albertosaurus.

Perhaps.  Let's wait for the details to come out.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796