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Re: Abydosaurus mcintoshi, a new sauropod from the Albian of Utah

On 25 February 2010 09:36, Jaime Headden <qi_leong@hotmail.com> wrote:
>   Furthermore, Chure et al produced a phylogeny that further complicated this 
> issue by failing to separate the taxa. At this point, the number taxa now 
> referred to the Brachiosauridae are done so based on the false assumption 
> that both species should be codified as a single entity. This is a major 
> problem arising from refusal to code from specimens explicitly (as OTUs) or 
> to use explicit specimens as the basis for species level OTUs.

In general, I strongly agree, and one of the thing I would really like
to see coming out of my own work is an end to the practice of coding
both well-known brachiosaur taxa together in a single OTU.  However,
in the current case what Chure et al. did make perfect sense: it would
be impossible for Brachiosaurus altithorax and Abydosaurus to form a
clade together, because their material does not overlap at all and so
they can't share any synapomorphies to the exclusion of Giraffatitan
brancai.  (Abydosaurus is know, or at least described, only from the
skull and anterior cervicals; none of that material is known for
Brachiosaurus).  It would still have been mildly interesting to see
which of the two establish brachiosaur taxa Abydosaurus clades with,
but not meaningfully informative.

>   No few of us on this list have argued in the past that phylogenetic 
> matrices should be produced using explicit specimens, in order to test the 
> complex of species as has been argued by some. I would actually like to think 
> that this debate resolves in someone, _anyone_ actually including the 
> specimen-based otus for each species or at least just species based solely on 
> type material and so forth as the only viable matrix to test from. This 
> should be the best sauropod phylogenetic study to be produced to date. It 
> should be done from scratch, and it should _NOT_ include characters that 
> occur only in a single "species" or specimen, as this does not test the 
> hypothesis of shared characteristics (an autapomorphy is great for typology, 
> but bad for phylogeny).
> Cheers,
> Jaime A. Headden
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> "Human beings, who are almost unique in having the ability to learn
> from the experience of others, are also remarkable for their apparent
> disinclination to do so." --- Douglas Adams (Last Chance to See)
> "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)
> ----------------------------------------
>> Date: Wed, 24 Feb 2010 15:19:21 -0800
>> From: tijawi@yahoo.com
>> To: dinosaur@usc.edu
>> CC: tijawi@yahoo.com
>> Subject: Re: Abydosaurus mcintoshi, a new sauropod from the Albian of Utah
>> Mike Taylor  wrote:
>>> But I do think it's enough evidence to have shifted the null hypothesis
>>> -- so that anyone who wants to challenge it really ought to make the
>>> effort to dig out some actual evidence themselves. What Chure et al.
>>> wrote -- "the identified differences have not been defended as
>>> separating genera, rather than species, populations, or individuals"
>>> -- really doesn't advance the discussion at all. It's an argument from
>>> laziness, and all it does is muddy the waters (and perpetuate the
>>> discredited notion that the Morrison and Tendaguru formations shared a
>>> fauna).
>> The discovery of _Abydosaurus_ might actually have provided a good 
>> opportunity to test the monophyly of _altithorax_+_brancai_. Instead, this 
>> monophyly was simply assumed by Chure &c, and _altithorax_+_brancai_ were 
>> therefore treated as a single OTU (_Brachiosaurus_) in the phylogenetic 
>> analysis.
>> Also, as mentioned by Mike, _altithorax_ is from the Morrison, and _brancai_ 
>> is from the Tendaguru. Thus, I would have thought that lumping the two into 
>> a single genus would require compelling morphological evidence. This isn't 
>> the case. IMHO, Taylor (2009) established a strong case for treating 
>> _brancai_ as a separate genus (_Giraffatitan_). It's only historical 
>> tradition that's holding the two together. If Janensch had *not* referred 
>> _brancai_ to _Brachiosaurus_, but had instead erected a separate genus, we 
>> wouldn't be having this discussion.
>> Cheers
>> Tim
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