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Re: Andrew McDonald response re: European iguanodonts



Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> Good call.  As for Troodon, I'd like to know what other troodontids have 
> mesial serrations, or serrated premaxillary teeth for that matter.  Not 
> Saurornithoides, Zanabazar (contra Barsbold, 1974),
>  Byronosaurus, Sinornithoides, Sinusonasus, etc..


Yes, _Troodon formosus_ can be diagnosed at the species level, insofar
as the teeth can be distinguished from the Asian troodontids - and
_Koparion_ too (no teeth are preserved for _Geminiraptor_).  However,
read on...


>  Troodon looks valid to me, regardless of how many species are encompassed by 
> what we call Troodon formosus.


This strikes me as a contradiction.  If several species share the same
dental characters that are characteristic of the _T. formosus_
holotype, then these characters can no longer be used to diagnose a
species.  Therefore, _T. formosus_ cannot be diagnosed at the species
level.  Ergo, it is a nomen dubium.


I say "if"... So far, ALL Campanian and Maastrichtian troodontid
material from North America has been assigned to _Troodon_.  This
includes teeth found as far north as Alaska and as far south as Texas
and New Mexico.  Now if every one of these specimens is conspecific,
then the dental characters used to diagnose _Troodon_ should be OK.
But... if the skeletal material indicates that more than one
troodontid species is represented in Campano-Maastrichtian North
America, AND they share the same kind of teeth as the _Troodon_
holotype, then I'm afraid _T. formosus_ is screwed.  It's _Iguanodon
anglicus_ all over again.



Cheers

Tim