Seismosaurus [was Re: Wilson & Sereno's Sauropod Phylogeny]

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

Dan Varner pleaded:

<And where's Seismosaurus? Help.>

  I have an opinion that came up with the publication of Dave
Gillette's _Seismosaurus: the Earth Shaker_ in accordance to it's
phyllogenetic position. This opinion is, of course, not my own, but
that of a little green man from somewhere called Zeeblonk who calls
himself Uuvuu....

  Anyway, to go on with this brain-implanted idea, the pelvis (yeah,
it all stems on the pelvis) of *Seismosaurus* has a few characters
that vary between two other taxa.

  1) anterior wings of the ilium are widely separated
  from the midline of the sacrum, as in the
  *Apatosaurus* specimen used and not in the
  *Diplodocus* specimen used for comparison.

  2) anterior margin of the pubis is not concaved
  (which it is in *Diplodocus*).

  3) 5th sacral vertebra (corresponding to the 1st
  caudosacral) below the margin of the posterior blade
  of the ilium (as in the *Apatosaurus* but not the
  *Diplodocus*).

  Now, I'd like comments on if any of these characters are relevant,
whether thay vary to any degree within the species or specimens of
*Diplodocus* or the species of *Apatosaurus* (or the genera assumed
therein).

  Anyway., my conclusion on this was that *Seismosaurus* would
actually be the intermediate form between *Apatosaurus* and
*Diplodocus*, in a clade like this:

--+--Diplodocidae
  +--+--Diplodocus
     +--+--Seismosaurus
        +--+--Apatosaurus

  Jaime A. Headden
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