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Re: [dinosaur] Latenivenatrix, new troodontid from Dinosaur Park Formation, Alberta (validity of Troodon)



Neotypes have been proposed for a large number of dinosaur taxa that
were founded on material now considered non-diagnostic.  These tend to
be 'iconic' dinosaurs that are well known in the public eye
(_Iguanodon_, _Allosaurus_, _Stegosaurus_, _Coelophysis_,
_Diplodocus_, _Plateosaurus_, _Cetiosaurus_, etc), but this is not
always the case (e.g., _Cetiosauriscus_, _Anchisaurus_ - neotypes
granted or proposed, despite having a lower public profile).  Not all
genera get this exalted treatment.  When _Titanosaurus_ was declared a
nomen dubium (in 2003) not a dog barked.

The genus _Troodon_ has a rather tortuous history.  During most of the
20th century, it was alternately regarded as either an ornithischian
(usually a pachycephalosaur) or some kind of a theropod.  Our concept
of the 'real' _Troodon_ did not come about until 1987, when the
well-known genus _Stenonychosaurus_ was synonymized with _Troodon_ (by
Phil Currie). Now that _Stenonychosaurus_ has returned as a valid
genus (30 years later), the prospects of a neotype for _Troodon_
appear remote.


On Thu, Aug 10, 2017 at 2:32 PM, Jaime Headden <jaimeheadden@gmail.com> wrote:
> History is replete with taxonomic names that were based on
> undiagnostic material, that effectively mean little beyond that they
> were named. Names, including *Ceratops* and *Stegosaurus* and
> *Allosaurus* have been found again and again to be wanting of
> diagnostic quality. Some more than others. For the argument of
> stability, for the mere fact that these names appear in old books and
> thus _must mean something_, these names have been preserved.
>
> The historian in us agrees: we should not abandon these names for the
> sake of their value; but their value is limited to the scope of
> history. For the pursuit of science, the names must also mean
> something tangible. We've decided diagnostic characters and
> differentiation are these best means for providing an objective
> measure -- and in that measure, these old names have been weakened,
> because the material that supported them was found wanting. Then, what
> we do is try to find some _other_ animal that fits our _newer_ idea of
> what that animal is, and prop it up. In the argument of "stability"
> (the age-old use of names built upon other names in the Linnaean
> system), we've kept these aged Nicodemus taxa trucking along.
>
> We have only a vague idea of *Astrodon*'s appearance; specimen drawers
> are littered with named scales and teeth whose material extends no
> further; and *Troodon formosus* is alive in the spirit of dinosaur
> paleo far longer than its brethren named by Joseph Leidy, revived by
> the _idea_ that it might be unique stratigraphically ... and for
> little other reason.
>
> Despite this, I can agree somewhat about holding off on saying
> anythong of *Troodon formosus* should there be a hope of finding
> topotypic material. But for all my optimism, I am also a cynic, and I
> would rather put aside that which does not serve us (communication,
> science, history) for something that does. That does, of course,
> depend on what happens to the TMF material. Until then, let us put
> aside *Troodon formosus*; while beautiful, it harms us by sustaining
> the image of animals removed from it in space and time when we know
> these factors have evolutionary meaning.
>
> On Wed, Aug 9, 2017 at 8:28 PM, Tim Williams <tijawi@gmail.com> wrote:
>> Jaime Headden <jaimeheadden@gmail.com> wrote:
>>
>>> To add to this, there remains doubt as to which tooth position the
>>> holotypic tooth derives, with the general region being mroe or less
>>> assumed by most authors. The tooth is well-preserved, but it's not
>>> terribly distinctive, which impairs almost any diagnostic method one
>>> may deem to use *Trodon formosus*. Leaving it to the realm of
>>> historical artefact would perhaps be wise. This means the Two Medicine
>>> Formation material may be best suited with a new name, if
>>> diagnostically supported.
>>
>>
>> If a diagnostic troodontid specimen turns up in the Judith River
>> Formation that includes teeth that resemble the holotype _Troodon_
>> tooth... it's been suggested that this could be referrable to
>> _Troodon.  So this specimen could possibly be used to uphold _Troodon_
>> as a valid genus.  But I don't think this is the best approach.  I
>> agree with you that, because of the nature of the tooth, and the fact
>> that the same kind of teeth occur in different troodontids, that
>> _Troodon_ is best consigned to history.  (The only alternative is to
>> create a neotype based on a diagnostic specimen, which means that the
>> original tooth could no longer be called _Troodon_.)
>>
>> I'd go one step further and abandon the name Troodontidae as well -
>> and revert to using Saurornithoididae as the name for this clade.  I
>> know it's permissible to retain family-level taxa founded on nomina
>> dubia (we still use Ceratopsidae, after all).  But I still don't think
>> it's a good idea (I also think the name Ceratopsidae should be
>> abandoned).  As a nomen dubium, _Troodon_ would not be a genuine OTU
>> (operational taxonomic unit), and so wouldn't be included in any
>> phylogenetic analysis - so its relationships can't be tested.  Also,
>> Saurornithoididae was erected explicitly to include _Saurornithoides_
>> and _Stenonychosaurus_ (now back from the dead as a valid genus).
>
>
>
> --
> Jaime A. Headden
> The Bite Stuff: 
> https://urldefense.proofpoint.com/v2/url?u=http-3A__qilong.wordpress.com_&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=DWFSKL-ii87wjLYdo0fMSno641fS6fu1igv_c5Tl_Hg&s=GGyAV_NwaCD_uUo6U4o4procjX1whI6LbOF3dydFKdQ&e=
>  
>
>
> "Innocent, unbiased observation is a myth" - P. B. Medawar (1969)