Re: Where have all the ornithischians gone?

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

David Peters (davidrpeters@earthlink.net) wrote:

<PAUP nests everything, as you know, so I'm going to get "a hit" somewhere.
Among 124 diapsids (with no more than a few in every clade) Lotosaurus comes
out closest to Silesaurus and Pisanosaurus.>

  What are the supporting characters? I'm really interested in this matrix,
now.

  Does this include the cruro-pedal material indicating a crocodylian-normal
astragalus and calcaneum (absent in *Silesaurus*, and unknown in *Pisanosaurus*
[but which bears a tibia showing a cranial facet for retention of the ascending
process of the astragalus and an astragalus much broader than the calcaneum])?
*Lotosaurus* also bears a curious preacetabular ala of the ilium rather unlike
even the condition in herrerasaurs and *Silesaurus*, which project cranially
and are broad but form a quadragular block anterior to the pubic peduncle;
instead, like several rauisuchians, *Lotosaurus* instead bears such a
quadrangular lateral "block" at the level of the pubic peduncle and there is no
blade like ala as in *Lesothosaurus* and all other ornithischians, which is the
distinguishing condition in ornithischians from other dinosaurs and is
currently optimized in PAUP as an apomorphy of the group (that is, if included,
and coded according to the fossils, this is what should occur). *Pisanosaurus*
lacks anything very intelligible about the ilium, and nothing is known of the
alae.

  A few other features in *Lotosaurus* argue for a different placement, so they
might be of interest, including dorsals bearing their parapophyseal pedicles
below the dorsal margin of the anterior face of the centrum (as well as the
posterior face), a femur and scapula of the same length, a distal scapula
craniocaudally broader in diameter than the proximal end and a
posterolaterally-oriented glenoid, which all indicate a largely semi-sprawled
quadrupedal static posture. I am also concerned about what had occured in the
19th and early half of the 20th century, and that was the conflation of
"croc-like thecodonts" and theropods into a single group, based largely on
similar ilia, and carnivorous jaws. This, of course, led Chatterjee to
speculate on the origin of theropods from crocodylomorphan rauisuchians (which
is where be put *Postosuchus*). Additional features include a slender,
non-sigmoid neck with short centra, a feature not conducive to the apparently
ubiquitous and poly-elemented neck of all basal dinosaurs; *Lotosaurus* has
only about 7 or 8 cervicals, and has 22-23 dorsals, which may mean the other
dorsal or two were incorporated into the 3-vertebral sacrum.

  Nonetheless, examining the codings and characters used instead of stating tha
PAUP* put them there is rather more of neccessity, since without this data,
such statements are almost meaningless.

<I was also surprised.>

  How many crurotarsans are included in the matrix?

  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)

"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 
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