Re: Acme genericometer (was RE: Gorgosaurus (was RE: Daspletosaurus t emporal...

["Jaime A. Headden" <qilongia@yahoo.com>]

--- Dinogeorge@aol.com wrote:
> In a message dated 8/7/02 2:08:22 PM Pacific Daylight Time, 
> TiJaWi@agron.iastate.edu writes:
> 
> << Two points:
>  
>  (1) Check the manufacturer's instructions for your genericometer. 
> Before
>  your genericometer can even be switched on, you have to first
> demonstrate
>  that the species constitute a monophyletic group.>>
> 
> I'm perfectly happy with paraphyletic genera (and higher taxa).
> Otherwise 
> Homo is simply a subgenus of some unicellular eucaryote genus.
>  
> << (2) The assumption that the lacrimal horn is a derived character that
> 
> unites
>  certain tyrannosaurines (sarcophagus, torosus, libratus) to the
> exclusion of
>  other tyrannosaurines (remotus, rex, bataar) has to be shown to be
> superior
>  to competing scenarios e.g. that the lacrimal horn is a primitive
>  tyrannosaurine character that was lost in rex, bataar and remotus. >>

<I addressed this issue in my Dino Frontline article on tyrannosaurids and
later in my email on the tyrannosaurid implosion. AFAIK lacrimal horns
occur only in the genus Albertosaurus, which is derived relative to
Tarbosaurus and all other known Asiatic tyrannosaurids. It's still an open
question (to some, anyway) whether Tyrannosaurus derives from
Albertosaurus or Tarbosaurus; if the former, then the lacrimal horn was
secondarily lost in Tyrannosaurus, if the latter, then the lacrimal horn
never appeared in Tyrannosaurus.>

  What, then invalidates the features shared between *D. torosus*, *T.
rex*, and *T. bataar* (with *T. efremovi*)? And then the shared features
between *T. rex* and *T. bataar* to support inclusion in a genus whose
type species lack ornamentation which cannot be validated? *A.
sarcophagus* is only half prepared bu lachrymals are not among the
material recovered. Lachrymal horns or prominences are known, however, in
all tyrannosaurines:

  *G. libratus* and *D. torosus* both possess laterally compressed
triangular processes, with the latter above the ventral lachrymal ramus,
and in the former projecting rostrodorsally and rostral to the ventral
ramus; in *T. bataar* and *T. rex*, these are laterally incrassate and
project caudally, above the orbit, caudal to the ventral ramus. Several
qualities of robusticity in the limbs and pelvis occur between *D* and *T*
that do not in *G*, and widening of the skull with transformation of the
mandible, including the cranial position of the ventral mandibular angle
(between dentary and angular), incrassate dentary and maxillary teeth, and
greater concavity of the ventral dentary margin. Even juvenile *T. bataar*
skeletons lack the adult *G.* morphology of the pelvis, with its extreme
sigmoid curvature, and the tibia is generally broader. They are also
grouped by smaller external nares, and these, at least some of them, have
been both published on in the last few years (especially Carr and
Williamson, 1999 [JVP 19] and Holtz, 2001 [Meso. Vert. Life]).

  *A. artunguis* may be *A. sarcophagus*, but if memory serves, study of
the latter will certainly shed light on what *Albertosaurus* Osborn truly
is. Carlify this, and one may certainly be able to figure out what species
may be referred to it. Otherwise, I stand with all other researchers
(including Paul) in keeping *D.* separate and next to *T. rex* and the
possible ancestral form from which the Nemegtian-Lancian tyrants derive.

----

  As for genericometrics, people have different ideas on how good their
stuff has to be to be a species. I am frankly annoyed with Lucas,
Sullivan, and Hunt in the almost lackadaisical manner in which various
taxa from New Mexico have been named, commented in part by Bennett (but
not, I believe, validly). In specific, *Revueltosaurus*, *Lucianosaurus*,
*Caseosaurus*, *Nodocephalosaurus*, *Eucoelophysis*, etc.. I personally
will side with Wagner (Jon) in that I would rather refer apomorphy-rich
species to the closest described species in which it agreed unless, as in
*Bagaraatan*, it did not really appear to resemble anything else. Only
then would I distinguish such a taxon with the next nomen up. Note I
abstain from using "genus" and "species" as invalid biological structures.
There really is no measure of a species. Until such evidence can be
produced that *G.* and *A.* can be clearly demonstrated as sympatric, they
should be retained as separate unique nomina. Containment of more than one
"species" in *A.* (sarcophagus and ?arctunguis; megagracilis is *D.*
apparently (Carr and Williamson)) depends on what *A. sarcophagus* is.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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