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Re: Australodocus a titanosauriform and other new papers



bh480@scn.org <bh480@scn.org> wrote:

> John A. Whitlock (2011)
> Re-evaluation of Australodocus bohetii, a putative diplodocoid sauropod
> from the Tendaguru Formation of Tanzania, with comment on Late Jurassic
> sauropod faunal diversity and palaeoecology.
> Palaeogeography, Palaeoclimatology, Palaeoecology (advance online
> publication)
> doi:10.1016/j.palaeo.2011.07.001
> http://www.sciencedirect.com/science/article/pii/S0031018211003579


I'm not qualified to comment on the merits of the assignment of the
cervicals named  _Australodocus_ to basal Titanosauriformes... but two
things come to mind:


Firstly, if _Australodocus_ is *not* a diplodocoid, does that mean
that all the diplodocid material from Tendaguru can be returned back
to _Tornieria_?


Secondly, I'm bewildered by Whitlock's reasoning for sinking
_Giraffatitan_ into _Brachiosaurus_:

     Although numerous morphological differences exist between B.
     altithorax and B. brancai, the genus Brachiosaurus has never been
demonstrated
     to be polyphyletic. Failing that, without a recognized criterion
for determining
     whether two taxa are either distinct palaeospecies or palaeogenera based on
     morphology alone, the decision to replace an existing name (in this case,
     Brachiosaurus) with a different one (Giraffatitan) must be seen as somewhat
     arbitrary. Because low-level palaeotaxa are perhaps best seen as convenient
     shorthand for facilitating discussion and not as equivalents of
neontological
     species or genera, it may be preferable to retain existing names whenever
     possible and thus maintain consistency with what is often decades
of previous
     scholarship.


Jee, I don't know about that.  I'm not sure that fossil genera and
species should be seen as "convenient shorthand for facilitating
discussion".  That seems excessively cynical to me - and lazy.  But
even if we follow Whitlock's advice (and I'm by no means suggesting
that we should), keeping _Giraffaititan brancai_ in _Brachiosaurus_ is
still a bad idea because it facilitates the *wrong* sort of discussion
- such as overstating the commonalities in the dinofauna between the
Morrison and Tendaguru.  (Ironically, Whitlock's study actually
emphasizes how different the Tendaguru environment was from the
Morrison, and highlights the impact this had on relative sauropod
diversity and browse regimes.)


Further,  to "maintain consistency with what is often decades of
previous scholarship" raises alarm bells, because a large portion of
this previous scholarship sometimes involved low standards for
taxonomy. And by 'low', read 'crap'.  Nearly a century ago, Tendaguru
taxa were lumped into established Morrison genera unless there were
compelling reasons not to (like _Kentrosaurus_).  It was Janensch's
default setting.  Janensch's reasons for assigning the Tendaguru
species _brancai_ to _Brachiosaurus_ were highly suspect, especially
considering that he had never seen the North American _B. altithorax_
material.  As further noted by Taylor (2009), "Because this assessment
did not describe specific derived characters shared between the
Tendaguru forms and _Brachiosaurus altithorax_, it would not be
considered a valid justification for the referral if published today."
 I aver we should be using current standards for dinosaur taxonomy,
not those exercised at the beginning of the last century.


To make the taxonomic issue more confusing, Whitlock's comparison of
_Australodocus_ to _Brachiosaurus_ concludes:

     Whether these differences are sufficient to differentiate them at
the generic level
     is uncertain. In a purely utilitarian sense, the argument is
unnecessary - the names
     as known serve to distinguish between the taxa, regardless of the
signifier used -
     and so _Australodocus_ is retained here.

So for the sake of tradition and convenience, African _Giraffatitan_
gets put back into North American _Brachiosaurus_ - but a second
presumptive brachiosaur from Tendaguru (_Australodocus_) remains as a
standalone genus...despite the stated opinion that it is "uncertain"
whether the two Tendaguru titanosauriforms can be differentiated at
the genus level?!  I'm not warming to this purely utilitarian approach
one bit.





Cheers

Tim