Re: Troodon and other problems (was Andrew McDonald response re: European iguanodonts

[Tim Williams <tijawi@gmail.com>]

Gregory S. Paul wrote:


> One good rule would be to no longer accept dinosaur teeth as holotypes,
> which does in Troodon. This would leave Stenonychosaurus inequalis as the best
> skeletal based species, not that the holotype of that is much to right home
> about either. The only skeletal remains that should be placed in the same
> species should be those that are from the same horizon, the rest should be S.
> sp. unless it becomes possible to either unite or distinguish them.


Yep.  In the case of _Troodon_, all and sundry North American Late
Cretaceous troodontid material have been funnelled into a single
tooth-based species (_T. formosus_).  This can't continue
indefinitely.


> It is not just a tooth problem. The holotype of Ornithomimus is extremely
> dubious at best. That of Struthiomimus is not great shakes either. All those
> taxa are sort of floating. There are the Mamenchisaurus and Omeisaurus
> messes. Diplodocus is a ticking time bomb. Don't get me started on some of the
> late Cret N Amer ankylosaurs. It's one thing after another.


If _D. longus_ turns out to be a nomen dubium, then _Diplodocus_
should definitely get a new type species (probably _D. carnegii_) -
the same way that a new type species was recently proposed for
_Stegosaurus_, and achieved for _Iguanodon_.


The type specimen for _Apatosaurus_ is no great shakes either: it's
from a young individual.  If _A. ajax_ turns out to be a nomen dubium,
then we go back to _Brontosaurus_ being a valid genus.... and wouldn't
that be fun?   ;-)


Jaime Headden wrote:


>  Greg, you're advocating low level of material in general, and conflating 
> teeth into that, allowing you to dismiss *Ornithomimus velox*. I do not think 
> that unless you can positively show it
> lacks any potential autapomorphy or autapomorphic suite, such an action is 
> useful.


In Greg's defense, I thought he was implying that the holotype of
_Ornithomimus_ might indeed lack autapomorphies (or a unique
combination of characters).


> This unfortunately coincides with the illusion of only complete specimens are 
> useful for taxonomy, as this is certainly not the case


Agreed.  As you say, only one autapomorphy or just one unique
combination of characters is need to diagnose a taxon at the species
level.




Cheers

Tim