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RE: Alamosaurus as biggest North American sauropod



  The problem with the principle that one can refer specimens to a given taxon 
simply because there is no evidence of any other taxon, is that this is both 
prone to temporal, recovery and observational biases. It is easy enough to say 
that there are no other taxa, but one cannot prove this case. It is not 
scientific that one simply says "Specimen A is Taxon Y because there's no 
evidence for Taxon Z when we only recognize Taxon Y." This bias can contribute 
to excessive lumping, and the inverse to splitting (recognizing any new 
material, regardless of its distinctiveness, as potentially a new taxon because 
it is differentiable, regardless of the potential for less taxa). The opposing 
situation likely plagues the proliferations of Wealden sauropod taxa from 
England, whereas sampling in latest Cretaceous Argentinian formations produces 
extensive multiple and sometimes closely related taxa (many of which are 
saltasaurines, andesaurines, etc.). The degree of relatedness can be based 
solely on resolution, and some might mitigate it by lumping several taxa 
together based on (guess what?) biases.

  One solution is that one should never refer material to a taxon if it cannot 
be directly compared to the type material. This is typically not a problem when 
you have a comparable series or bonebed, and must select a partial type, as 
occurs with *Silesaurus opolensis* or *Falcarius utahensis*. But the problem 
arises that material, as happened with *Daemonosaurus chauliodus*, is simply 
assumed to be part of another specimen prior to in depth examination. This 
might split material off among previously recognized taxa, or recognize 
variation among conspecifics.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


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> Date: Thu, 8 Dec 2011 08:30:22 -0500
> From: martyniuk@gmail.com
> To: j.falconnet@gmail.com
> CC: dinosaur@usc.edu
> Subject: Re: Alamosaurus as biggest North American sauropod
>
> I don't see the issue with using parsimony. In fact I have kind of an
> issue when people don't use it. If the remains can't be differentiated
> from _A. sanjuanenis_, and there is no evidence to suggest multiple
> taxa were present in this environment, it should be considered _A.
> sanjuanenis_ until evidence to the contrary can be produced. "When you
> hear hoofbeats think horses, not zebras." If an when a second sauropod
> taxon is positively identified from this stratigraphic and geographic
> level, the remains in question can be either left as they are,
> re-assigned, or considered dubious.
>
> Assuming from the outset that any fragmentary remains may represent a
> new taxon rather than being conservative and using parsimony to assign
> them to an already known taxon from which they cannot be
> differentiated just leads to over-inflated estimates of diversity, as
> in the paper discussed here:
> http://dinogoss.blogspot.com/2011/01/scientific-anachronism-and-why.html
>
> Matt
>
> On Wed, Dec 7, 2011 at 5:10 PM, Jocelyn Falconnet <j.falconnet@gmail.com> 
> wrote:
> > From what I understood in the paper, here is the reasoning of the authors
> > for assigning these three bones to *Alamosaurus*:
> >
> > - Late Cretaceous sauropods are all titanosaurians
> >
> > - cervical vertebra with wide cotyle =>  as in *Alamosaurus*,
> > *Malawisaurus*, and *Puertasaurus*
> >
> > - cervical vertebra with lateral pneumatic fossae =>  as in *Alamosaurus*,
> > *Rapetosaurus*, *Malawisaurus*, and *Saltasaurus*
> >
> > - no relevant feature on the caudal vertebra and femur
> >
> > - no evidence for more than one sauropod taxon from the Maastrichtian of US
> >
> > "We therefore refer the new specimens to *A. sanjuanenis*, based on
> > stratigraphic and geological parsimony, and the similarity of SMP
> > VP−1850 to cervical vertebrae from Texas (Lehman and Coulson 2002), and
> > SMP VP−1625 to the caudal series from Utah (Gilmore 1946)."
> >
> > Stratigraphic and geological parsimony ?! WTF, if I may say so !
> >
> > I recognize that these remains are indeed very interesting for indicating
> > the presence of a giant sauropod in the Maastrichtian of the US and their
> > possible belonging to *Alamosaurus*, but I think the authors are too much
> > optimistic, taxonomically speaking. No need to be a specialist to understand
> > that they belongs likely to a titanosaurian but there is no positive
> > evidence for its assignment to *Alamosaurus* - and if stratigraphy or
> > geology were taxonomically relevant, we would know it ! Hell, there is not
> > even a "cf." or an "aff." in the identification of the specimens. Of which
> > two are... indeterminate titanosaurians (just read the text).
> >
> > So... please, don't do that anymore.
> >
> > Time to go to bed,
> >
> > Jocelyn
> >
> > Le 07/12/2011 18:14, Ben Creisler a écrit :
> >
> >
> >> From: Ben Creisler
> >> bscreisler@yahoo.com
> >>  A new paper in Acta Palaeontologica Polonica:
> >>  Denver W. Fowler and Robert M. Sullivan (2011)
> >> The first giant titanosaurian sauropod from the Upper Cretaceous of North
> >> America.
> >> Acta Palaeontologica Polonica 56 (4), 2011: 685-690
> >> doi:10.4202/app.2010.0105
> >> http://app.pan.pl/article/item/app20100105.html
> >>
> >> Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the
> >> largest dinosaur so far discovered and is one of several giant 
> >> titanosaurian
> >> sauropods known from the Upper Cretaceous of South America and Asia, but
> >> surprisingly not from North America. Here we present the first evidence of
> >> giant titanosaurian sauropods from the Upper Cretaceous of North America:
> >> two enormous vertebrae and a partial femur, from the Naashoibito Member of
> >> the Ojo Alamo Formation, New Mexico, and referred to Alamosaurus
> >> sanjuanensis. One of the new vertebrae, a posterior cervical, is comparable
> >> in size to a posterior cervical described for Puertasaurus: an
> >> Argentinosaurus−sized titanosaurian from the Maastrichtian of Argentina.
> >> This makes A. sanjuanensis the largest dinosaur from North America, and
> >> among the largest in the world. These findings indicate that A. 
> >> sanjuanensis
> >> is diagnosed based on immature remains, which may have implications for
> >> cladistic analyses.
> >
> >