Re: Sereno's (2005) new definitions

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<Autapomorphies = derived characters unique to itself (auto- = self).>

  A better definition could be "a character not shared by proposed outgroups to
[defined] taxon/clade content."

  An issue with the use of "unique" can be highly dangerous, since many
autapomorphies may be unique only when excluding taxa in consideration, and
some taxa, such as *Archaeopteryx* (which has been considered a metataxon) have
features or shapes of the bones which are not shared by at least several taxa
stemward or crownward. Perhaps a taxonomic distanct of 2 or 3 can be used, a
"bubble" that defines the use of "unique" in considerations of autapomorphies.

<(For example, if *Lagosuchus* were older than *Marasuchus*, it could be its
ancestor.)>

  They are from the same formation. In fact, they are from the same locality
and quarry. Nearly the entire Los Chañares fauna are from the same small area
and are thus tightly constrained. *L. talampayensis* non-hindlimb features are
questionable, as a block of matrix has produced no less than three different
taxa, including the type of *M. lilloensis*, as well as some crocs.

  It is actually possible for *L. talampayensis* and M. lilloensis* to be the
same species. The variation in limb design can be considered variation in the
taxon, though constrained locomotory features tend not to vary much at all
within populations or species, based on extant constraints as seen in mammals
and birds, but rather proportions are more likely to change than gross
morphology. This allows us to make predictions such as that proportionate
clines in log plots may accurately represent species consistency in specimens
included. Sereno and Arcucci were aware, I think, that such variation was
possible, but because *Lagosuchus lilloensis* had been named as a new taxon
already, but the type of *Lagosuchus talampayensis* was not diagnostic, *L.
lilloensis* required a new name anyway. Frankly, we should do this for all
problematic types, but time will tell how viable this is.

  Cheers and Merry Joyous Happy Dienatisolstinvichrismachanukwanzakahmadan,

Jaime A. Headden

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


                
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