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Re: What ever happened to Deinodon?



From: Saurischia@aol.com

 > I was wondering if someone could summarize for me what criteria
 > caused reclassification of Tyrannosaurus and his kin over the years.

Basically it was shown that tyrannosaurs had more *detailed*
features in common with the coelurosaurs than with the "carnosaurs".
[I do not have Dr. Holtz's data set here to give a definitive list
of shared features however].

 >  Why were the Theropod infraorders Coelurosauria and Carnosauria
 > dropped - was the line drawn between them too ambiguous?

Partly, but also partly because evolutionary analysis showed that
the Carnosauria as originally constituted was a grab-bag of "unrelated"
forms (that is polyphyletic in formal terms), not a natural group.

Note, I still retain a more limited Carnosauria in my classification.
My Carnosauria is a combination of the megalosaurs and the allosaurs.
People like Dr. Holtz would reject this grouping because it does not
include ALL of the descendents of the common ancestor (that is, in
technical term, it is paraphyletic).

 > I've noticed the Ornithosuchidae were extracted from Carnosauria and 
 > given a suborder to replace the Pseudosuchian Thecodonts.  Is this 
 > Ornithosuchia suborder now believed the common ancestor between 
 > Saurischia and Ornithoschia? 

No, they are not considered a side branch - perhaps not even all
that close tot he ancestry of dinosaurs.  They were never securely
included in the dinosaurs: many experts always questioned that
placement.  It is now clear that the doubters were right, and these
forms were not dinosaurs.

 > And I remember Tyrannosauridae was once also referred to as
 > Deinodontidae, and Gorgosaurus as Deinodon.

This is because some the name Deinodon is old, older, certainly, than
Gorogosaurus.  Unfortunately the name was given to a single tooth,
and tyrannosaur teeth all look the same, so there is no real way
to tell *which* tyrannosaur is really Deinodon.  For this reason the
name is no longer used for anything except a few isolated tyrannosaur
teeth. (Nowadays such teeth are not given a genus name, they are just
labeled "tyrannosaur teeth").

 > (Am I right in assuming Gorgosaurus and Deinodon are now both
 > synonymous with Albertosaurus?

Nope.  Only Gorgosaurus is conisdered (by some) a synonym of
Albertasaurus.

Deinodon is considered "indeterminate" - in formal parlance it
is a "nomen dubium".  It is a synonym of *nothing*.

 > At one point Albertosaurus and Gorgosaurus were considered different
 > animals.)

Some still do consider them separate.

They are certainly anatomically and ecologically *very* similar.
But since the genus Tyrannosaurus is apparently descended from a
species in this group, it is probably paraphyletic (as described
above), and so people who reject paraphyletic taxa must split
Albertasaurus into two genera, and it turns out one of these can
be called Gorgosaurus.

 > As I'm not current in paleontology, I find myself getting confused,
 > especially since my library is outdated.
 > 
 > Why do new genus names sometimes replace older ones? 

They don't.  That is utterly forbidden.

> I always liked the name Brontosaurus better than Apatosaurus.

Unfortunately for you, the name *Apatosaurus* is the older of the two!
Thus, as long as all of the species involved are considered to belong
to one genus, the name of that genus *must* be Apatosaurus, since other-
wise we *would* be replacing an older name with a newer one.

 >  (I remember there was an issue over a missing Brontosaurus skull -
 > was that a factor?)

Nope, not at all.  Thay just moved Apatosaurus from its own family
of sauropod to the family Diplodocidae.

 > I always liked the name Trachodon too, perhaps only due to childhood
 > familiarity.  That's a name I NEVER see anymore.  I thought
 > Trachodon was renamed Anatosaurus but I have one *old* book that
 > lists them as two separate specimens, and a newer book that doesn't
 > list Trachodon at all.

The Trachodon situation is identical to the Deinodon one - Trachodon
was named for a single tooth!  And hadrosaur teeth are also all very
similar.  Thus the name Trachodon refers to an *unidentifiable* form:
it is also a momen dubium.

Ironically, the original Trachodon tooth is now held to be probably
the tooth of a *crested* hadrosaur, not a flat-headed one like
"Anatosaurus" (now moved to Edmontosaurus).

 > And at some point in the past I thought Antrodemus was going to
 > replace Allosaurus, but I'm glad to see that it hasn't.

Because it has been determined that Antrodemus is based on an
indeterminate fragment; that is Antrodemus is also a nomen dubium.
[Though in this case the fragment is NOT a tooth].

If Antrodemus were NOT a doubtful name, and were found to be the
same as Allosaurus, then indeed we would be required to drop the
use of Allosaurus in its favor, as it is an *older* name than
Allosaurus.

All of this will be in my Web site, hopefully by sometime this fall.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.