Re: Alwalkeria

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

ekaterina A (a_ekaterina@yahoo.com) wrote:

<So the original claim that Guaibasaurus was a basal saurischian does not
seem to hold anymore. That honor seems to have gone to Hererrasaurids and
Eoraptor.>

  Well, this doesn't really resolve the basal saurischian, actually. There
are still features that allocate, even based on pelvic anatomy, that
herrerasaurids are basal theropods, whereas *Guaibasaurus* and *Eoraptor*
appear distinct in this regard as non dinosaurs with features of basal
sauropodomorphans, or animals closer to theropods than general to any
saurischian. The pelvis of *Guaibasaurus* is still far more like that of
*Thecodontosaurus* than it is to other basal theropods. *Herrerasaurus*
also appears to have severely modified the pelvis, compared to the more
basal-appearing *Staurikosaurus*. The latter may not actually be a
herrerasaurid, as it seems to be included in general in recent analyses.
Other herrerasaurids, such as *Chindesaurus* and *Caseosaurus*, have more
derived ilia than does *Staurikosaurus* relative to *Herrerasaurus*, which
we assume to be a derived member on the basis of its pubis.

  *Guaibasaurus*, along with *Saturnalia* and *Eoraptor*, apppear to
require more study to resolve their relationships. Fortunately, an entire
descriptive and phylogenetic analysis of the last is in prep, and this
will certainly involve the most in depth work on basal theropods so far
known. How this will reflect basal saurischians and dinosaurs in general
is not known. The story has not been written yet, it seems.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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

__________________________________
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!
http://sbc.yahoo.com