Re: What ever happened to Deinodon?

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

Gadzooks, where do I start...?

Well, these are my views on the subjects you raised.

The reclassification of _Tyrannosaurus_, _Ornithosuchus_, and the 
redefinition of Coelurosauria and Carnosauria occurred simply because 
the methods of classification changed.  Instead of basing 
classifications around the overall size and shape of dinosaurs, 
paleontologists began looking at the more subtle details of dinosaur 
anatomy - arrangement of the bones that make up the braincase, shape 
of the limb and hip bones, position and number of fossae in the 
cranial elements, things like that.  Most of these characters are 
extremely esoteric, and are little perplexing to amateur 
paleontologists (like me - I've only just worked out what an 
obturator notch is).  And, I suspect, they're a headache for serious 
paleos too.  But they give a much more accurate view of dinosaur 
phylogeny.

Hence, _Ornithosuchus_ was shown not to be a dinosaur at all.  But 
it lies somewhere not too far from the origin of the Dinosauria.  A 
group was created to accommodate ornithosuchids, "lagosuchids", 
dinosaurs and pterosaurs, and this group was called the 
Ornithosuchia.  The Ornithosuchia did not replace the Pseudosuchia; 
both were just redefined.  Same goes for the Coelurosauria and 
Carnosauria.  

So too, a closer look at tyrannosaur anatomy led many paleontologists 
to believe that they were really more closely related to groups like 
the troodontids and ornithomimids, not to other big theropods like the 
megalosaurids and allosaurids.

_Deinodon_ is a pretty shoddy genus since it's based on lousy 
material (a few teeth I believe).  It was not possible to define 
_Deinodon_ as a distinct genus, since (from what is know of it), 
_Deinodon_ has no unique features that could distinguish it from 
genera like _Albertosaurus_ or _Gorgosaurus_.  Hence, _Deinodon 
horridus_ is best regarded as a _Nomen dubium_ (dubious name).  And, 
since you cannot name families after _nomina dubia_, the name 
Deinodontidae is defunct.  Tyrannosauridae wins out.

(Yes, yes, I know the Ceratopsidae, Hadrosauridae, and possibly the 
Titanosauridae are all named after genera based on indeterminate 
material, but that's another can of worms I don't really want to 
open here.)

Some generic names replace other generic names (like the 
_Apatosaurus_ and _Brontosaurus_ story), because when two genera are 
found to be the same (like when the material on which genus is based 
is found to be more-or-less identical), the genus that was named 
first takes priority, and the other genus is relegated to a junior 
synonym.  _Brontosaurus_ (alas) was sunk as a junior synonym of 
_Apatosaurus_.

_Antrodemus_ was named before _Allosaurus_, but the former is a 
_nomen dubium_.  _Antrodemus valens_ was based on an incomplete 
tailbone which could belong to _Allosaurus_, but it could also belong 
to a number of other big theropods.  Hence, _Antrodemus_ gets 
consigned to the taxonomic wastebasket.  Here it can join 
_Deinodon_, _Trachodon_, _Ceratops_, and a host of other dinosaur 
genera based on indeterminate remains.
 
Hope that helps. 

Tim