Re: Sinosaurus (theropod from Early Jurassic of China) braincase anatomy (free pdf)

[Tim Williams <tijawi@gmail.com>]

I'm fine with deciding names by fiat, when it's workers in the field
(paleontologists) who decide which specimens should carry the name,
albeit on a case-by-case basis.  Establishing a neotype is important
for entrenched genera such as _Iguanodon_, _Allosaurus_,
_Plateosaurus_, and _Stegosaurus_.  It may yet be necessary for
_Diplodocus_, another well-known genus.  In these cases, a neotype
helps ensure the continuity of a well-known genus, when the type
specimen is deemed to be indeterminate or of dubious diagnostic value.
I think this approach is good for the long-term stability of a name -
including in cases where the original type specimen is possibly
diagnostic, but of exceedingly poor quality.

But I don't always think this process is necessary - as in the cases
of _Coelophysis_ and _Cetiosauriscus_, which also came before the
ICZN.  For _Coelophysis_, I agree that a neotype might have been
necessary; but one could argue that the specimen chosen as neotype
(the holotype of _Rioarribasaurus_) was inapt.  For _Cetiosauriscus_,
I don't think this genus had accrued enough cachet to deserve being
salvaged as a valid genus via the designation of a neotype; the ICZN
disagreed.  But again, it was workers in the field who petitioned the
ICZN.

For _Sinosaurus_,  I agree that the type specimen looks very iffy -
but I'll trust to Currie &c to explain why they chose to refer
_Dilophosaurus sinensis_ to _Sinosaurus triassicus_, rather than make
the former the holotype of a new genus (which has the benefit of an
excellent type specimen).  I do agree it will take some "some amazing
dental autapomorphies " to justify the referral of _D. sinensis_ to
_Sinosaurus_.  If these shared characters are anything less than
amazing, I doubt _Sinosaurus_ will last the distance as a valid genus.
Let's check in at the end of 2034, and see how _Sinosaurus_ is faring!
  :-)

Time-honored and fairly well-known genera that are based on dubiously
diagnostic material have often been discarded as nomina dubia - such
as _Titanosaurus indicus_.  Here, a case could have been made to refer
_Jainosaurus septentrionalis_ to _T. indicus_, and retain the latter
as a valid taxon.  Instead _Titanosaurus_ has been junked in favor of
_Jainosaurus_.  So there are parallels to the _Sinosaurus_/_D.
sinensis_ situation.  In general, because this approach is based on
the discretion of individual workers, there is a great deal of
inconsistency in the literature.  But I still think the decision
should be left to individual workers, and nomenclatural stability be
the major determinant.  For example, I'd hate to see _Tyrannosaurus_
sunk into _Manospondylus_, simply because the crappy type specimen of
_Manospondylus_ was deemed by someone to be diagnostic at the genus
level.




Cheers

Tim








On Wed, Dec 17, 2014 at 7:18 PM, Mickey Mortimer
<mickey_mortimer111@msn.com> wrote:
> It's great to have more info about this theropod, but does anyone else find 
> it backwards that we're getting this series of detailed papers on 'Sinosaurus 
> triassicus' but based on Dilophosaurus sinensis specimens, before any 
> evidence has even been presented that sinensis is a synonym?  Maybe Currie et 
> al. have some amazing dental autapomorphies up their sleeves, in which case 
> ignore the rest of what I write here.  But the holotype of Sinosaurus 
> triassicus is REALLY fragmentary- a maxillary fragment four alveoli long, 
> another three alveoli long that Young though probably belonged to the 
> maxilla, a third jaw fragment with two alveoli that Young couldn't even 
> identify to the element, and three teeth.  These are the kinds of remains 
> that are generally not considered diagnostic between pseudosuchians and basal 
> theropods, let alone diagnostic for particular basal theropod species.  I 
> fear the rationale will be along the lines of "the teeth are identical and 
> they're from the same f
 or
>  mation", but we don't let this work for other taxa (Suchosaurus vs. 
> Baryonyx, Antrodemus vs. Allosaurus, Manospondylus vs. Tyrannosaurus, etc.), 
> and would be surprised if the Sinosaurus holotype could be distinguished from 
> e.g. Cryolophosaurus or Dracovenator.  It's easy to then imagine someone 
> twenty years down the line realizing this after Sinosaurus triassicus has 
> been the established name for the Lufeng skeletons, then petitioning the ICZN 
> to make a Dilophosaurus sinensis skeleton the neotype of Sinosaurus.  This 
> would be deciding names by fiat (look at the Allosaurus, Stegosaurus and 
> Plateosaurus examples today) instead of by which specimens are diagnostic, 
> which is not how I think it should be done.
>
> Mickey Mortimer
>
> ----------------------------------------
>> Date: Tue, 16 Dec 2014 11:27:01 -0800
>> From: bcreisler@gmail.com
>> To: dinosaur@usc.edu
>> Subject: Sinosaurus (theropod from Early Jurassic of China) braincase 
>> anatomy (free pdf)
>>
>> Ben Creisler
>> bcreisler@gmail.com
>>
>> A new paper (in open access at the link):
>>
>>
>> Xing Lida,
>
>> Zhang Jianping, Wang Tao, Michael E. Burns & Dong Zhiming (2014)
>> Braincase Anatomy of the Basal Theropod Sinosaurus from the Early
>> Jurassic of China.
>> Acta Geologica Sinica 88(6):1653-1664 (English Edition)
>> http://www.geojournals.cn/dzxben/ch/reader/view_abstract.aspx?file_no=201406002&flag=1
>>
>>
>>
>> The neuroanatomy of the mid-sized theropod Sinosaurus triassicus from
>> the Lower Jurassic Lufeng Formation, Lufeng Basin in Yunnan Province,
>> China was studied using X-ray computed tomography. The braincase is
>> characterized by a large supraoccipital knob that is capped by a
>> posterior projection of the parietal and two external foramina for the
>> caudal middle cerebral vein, which is completely enclosed by the
>> supraoccipital. The basicranium has well defined, short basipterygoid
>> processes that project ventral to the basal tubera. The basisphenoid
>> is expanded, projects posteroventrally, and is pierced by four
>> pneumatic recesses. The endocranial morphology resembles that observed
>> in other basal theropods—in particular some allosauroids—and has a
>> strongly marked pontine flexure and a large dorsal expansion. The
>> inner ear morphology is also similar to that observed in other basal
>> theropods, with slender semicircular canals. The anterior semicircular
>> canal is 20% larger than the posterior semicircular canal, and the
>> angle formed between them is less than 90° when seen in dorsal view.
>