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



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.

On Wed, Aug 9, 2017 at 3:35 AM, Thomas Richard Holtz <tholtz@umd.edu> wrote:
> Actually, the writing has been on the wall for Troodon for a while. Ever
> since Talos was described and Larson & Currie's
> (https://urldefense.proofpoint.com/v2/url?u=http-3A__journals.plos.org_plosone_article-3Fid-3D10.1371_journal.pone.0054329&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=RyKvz9pVF6JJM5gZBP9yY0s19G_oC7xDK0KpuXJtKho&s=uSgxlEFbI-1D77iSfc2oRZIJ4QuTPxju1ALLCEw46z4&e=
>  )
> morphometric study of theropod teeth, it's been clear that there was a
> diversity of troodontids in Campanian North America. And the Asian record
> shows multiple troodontids living side by side.
>
> On Tue, Aug 8, 2017 at 10:29 PM, Tim Williams <tijawi@gmail.com> wrote:
>>
>> Ben Creisler <bcreisler@gmail.com> wrote:
>>
>>
>> > Troodon formosus nomen dubium?
>>
>>
>> Things aren't looking good for _Troodon_.  It's likely heading the
>> same way as _Deinodon_ and _Ceratops_ (two nomina dubia also from the
>> Judith River Formation).
>>
>> The authors (van der Reest and Currie) come very close to declaring
>> _Troodon formosus_ a nomen dubium... but don't quite do it.
>> Nevertheless, they concur with the findings of recent studies (e.g.,
>> Zanno et al. 2011; Larson and Currie, 2013 - both cited) that the
>> teeth are not distinguishable (diagnostic) at genus level for a number
>> of troodontids, including _Troodon formosus_.  Therefore, because the
>> holotype includes only teeth, _T. formosus_ would technically be a
>> nomen dubium.
>>
>> But the authors provide some hope for _T. formosus_, if future
>> material from the same formation and locality can be referred to this
>> species...
>>
>> "Although the validity of _Troodon formosus_ may be contentious,
>> future discoveries may provide the osteological information required
>> to sort out true relationships in North American troodontids. For any
>> specimens that are positively identified as _Troodon formosus_,
>> however, they must originate from the Judith River Formation in the
>> region from where the holotype was recovered."
>>
>> Maybe.  The implication is that new diagnostic material could be
>> referred to _T. formosus_ to keep it alive as a valid taxon.  But it's
>> not that simple.  Even if troodontid material is recovered from the
>> JRF that includes diagnostic bones along with teeth that match _T.
>> formosus_, it may not be enough to save _T. formosus_.  A neotype
>> would probably have to be designated for _T. formosus_ based on this
>> new (topotypic?) material.  This could happen, but there's no
>> guarantee it will (even if potentially referrable material is
>> discovered).
>>
>> A similar situation came up for _Ceratops montanus_, another
>> time-honored taxon named from non-diagnostic material.  The only hope
>> of keeping _C. montanus_ alive as a valid genus and species is based
>> on new/referred material.  The best chance was the diagnostic
>> chasmosaurine specimen CMN 57081 from the JRF, which matched the _C.
>> montanus_ type material both osteologically and stratigraphically.
>> The study that described this material (Mallon et al. 2016
>> DOI:10.1371/journal.pone.0154218) actually stated "It is possible -
>> even likely, given their close stratigraphic and geological
>> association - that '_Ceratops_' and CMN 57081 are the same species".
>> However, they went on to say "without conclusive evidence for such, it
>> is preferable to erect a new species for CMN 57081."  So CMN 57081 was
>> granted its own genus and species _(Spiclypeus shipporum_), rather
>> than being referred to _Ceratops montanus_.  I reckon the same thing
>> could happen if a diagnostic JRF troodontid specimen was discovered in
>> the vicinity of the _T. formosus_ type locality.  Unless a neotype was
>> nominated (and approved), there would always be doubts over whether it
>> should be referred to _T. formosus_.
>>
>> Objectively, there's no good reason *not* to treat _Troodon_ any
>> differently from _Deinodon_ or _Ceratops_.  Alas, _Troodon_ is a
>> goner.
>
>
>
>
> --
>
> Thomas R. Holtz, Jr.
> Email: tholtz@umd.edu         Phone: 301-405-4084
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