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RE: PDF-request: Original description of Lagosuchus and/or Marasuchus



David Marjanovic's definition (as taken on by other PT proponents) makes sense 
in this case, as for a single species, an ancestor would be assumed (as it is 
unknown) to lack said feature, and thus the definition allows said feature to 
be diagnostic to the species exclusively, as to any other taxon. Classic uses 
of the term have allows only a feature that is completely unknown in ANY animal 
to be used as "autapomorphies."

  In this way, the first definition allows elongated radiale and ulnare to be 
autapomorphic for a derived clade of crocodylomorphans referred to as 
"Sphenosuchia," while the latter would require me to pick a specific feature no 
croc anywhere had to diagnose the clade I chose; thus, if the feature appears 
somewhere else, it is no longer autapomorphic.

  I am not sure which version of this term Dave Peters is using, or if he's 
using a generalized term for a feature being included in the diagnosis. No 
matter, though, as my replies on the supposed novelties as exclusive features 
of *Vancleavea* versus the convergent anatomy with other aquatic diapsids 
shoudl allow understanding; even if convergent, the aquatic adaptations of 
*Vancleavea* are nonetheless autapomorphic within the framework of that taxon 
as a stem archosaur.

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)





----------------------------------------
> Date: Tue, 13 Apr 2010 16:40:31 -0600
> From: William_Parker@nps.gov
> To: dinosaur@usc.edu
> Subject: Re: PDF-request: Original description of Lagosuchus and/or Marasuchus
>
> From: David Marjanovic 
>
>>>"Autapomorphy" just means "character state present in the first member
>>>of a clade and absent in its last ancestor". Every parsimony-informative
>>>character, thus, has a state that is autapomorphic of a clade.
>
> This is a much different definition of Autapomorphy than I am used to,
> which is a character state that is unique to a terminal taxon and thus
> uninformative in a phylogentic analysis. I believe this is the definition
> that David Peter's is also following when it describes them as "weird".
>
> I would think that the term apomorphy is what you described above.
>
>
>
> ************************************************************************
> Bill Parker
> Vertebrate Paleontologist
> Division of Resource Management
> Petrified Forest National Park
> P.O. Box 2217
> 1 Park Road
> Petrified Forest, AZ 86028
> (928) 524-6228 x262
>
>
>
                                          
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