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Re: PISANOSAURUS



In a message dated 97-09-06 17:48:40 EDT, Tetanurae writes:

<< The pelvis of _Pisanosaurus_ is known only from a matrix impression,
 so we have little idea what it was really like. But what looks like an
 impresion of a propubic pelvis is much more likely to be that of a pelvis in
 which there is a fairly well developed prepubic process. This is how
 Bonaparte interpreted it in his original description. Everything else known
 about _Pisanosaurus_ suggests this.>>
 
 I find this extremely unlikely.  Even though it is simply a matrix
impresison, it clearly shows the pubis going straight away from the
acetabulum at about 20 degrees forward of the verticle axis of the pelvis.
 _Pisanosaurus_ was propubic as much as _Allosaurus_ or _Plateosaurus_ are --
unless of course the pubic shaft took an increadible U-turn somewhere
mid-shaft where we can't see it.... >>

This isn't clear at all, but in any event the matrix was destroyed during
preparation and the information is not recoverable, so we might as well stop
discussing this. We're just going to get nowhere; we'll just have to wait
until a more complete specimen turns up. But it wouldn't surprise me terribly
if the pelvis was similar to that of prosauropods... I see no similarity
between the pelvis that Bonaparte (or was it Casamiquela?) drew for
_Pisanosaurus_ and the pelvis of _Allosaurus_. The >rest< of the skeleton,
particularly the teeth, suggests heterodontosaurian relationships for
_Pisanosaurus_. The feet are like those of prosauropods and segnosaurs:
metatarsals serially overlapping proximally, not bundled; astragalus with
laterally situated ascending process (huge in segnosaurs, of course, and
subdued but present in prosauropods and _Pisanosaurus_).