Re: Where did my posting go?????? and Info

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

Matt Bonnan wrote <...this nice message about
Marasuchus, addressing some things about the calcaneum
and antitrochanter and ... ah, crud. I don't have the
time and energy right now to write again -- I guess it
was sent to the great void in the sky. =) =(>

  It _really_ gets annoying when someone writes a post
like this after a couple hours and it gets lost in the
datastream ... yeah, it's happened to me, too.

  <To quickly address Jaime Headden's statement that I
am saying something untrue about Marasuchus, let me
clarify. While there is a calcaneal tuber present in
Marasuchus, it is so reduced and small that it's
overall effect on locomotion would be comparable to
what's going on in dinosaurs -- nothing. In fact, the
"tuber" is merely a small bump which faces posteriorly
and is roughly equal in size and prominence to the
posterior tuber on the distal end of the fibula, where
the big plantarflexors are surely not inserting.>

  Not to say you were lying, Matt, which I certainly
hope I didn't imply! But to say that the statement was
not correct given my perusal of the paper in question.
 
  <This condition is no where near what we see in
Alligators, let alone the big leaping kangaroos. The
calcaneum is not providing the sort of lever arm you 
see in jumpers. Furthermore, we've got the simple
hinge-like joint in Marasuchus as we do in other dinos
and the metatarsals appear to have been held
vertically, as in other dinos.>

  This "bump" is in the form of a small ridge, and
while certainly not in the league of those great big
levers in ricochetters like 'roos or even simple small
ones in your tabby, it is certainly larger than
anything in Dinosauria, and would have reasonably
conferred some biomechanical effect above the
dinosaurian-pterosaurian ankle, something closer to
them certainly than to crocodiles, but you get my
meaning.

  <Please have a good look at the reconstruction of
the Marasuchus skeleton, and note that the tiny tuber
on its calcaneum contributes next to nothing at the
ankle joint -- this joint is the hinge-like thing we
see in all other dinosaurs.>

  But the point is, it does seem to contribute some
effect. A good test would be to find out what this
effect could have been expressed as, or if in fact
there was any biomechanical effect at all.
 
  <By the way, the head of the femur is cylindrical in
Marasuchus. So as not to be accused of saying
untruths, Sereno and Arcucci describe the top portion
of the femur as "egg-shaped." The femoral head is NOT
spherical-->

  I didn't say it was. I said semi-spherical,
conferring a measurable amount of lateromedial
movement beyond that of, say, *Coelophysis*, but less
than that of *Dimorphodon,* given the relative shape
of the _caput_ in all three taxa, using Colbert (1989,
1990) and Padian (various) and Unwin (1999 springs
easily to mind), so *Marasuchus* falls between the two
in femoral head shape. But this is also be related to
the fact that the acetabulum has only partial
fenestration, unlike in pterosaurs or crocodilians.

  <--and is longer lateromedially than
anteroposteriorly.>

  As Sereno and Arrucci, and Sereno et al. (1993)
suggest, *Marasuchus* falls right smack dab in the
middle of Ornithodira, a very near (if not perfect)
transitional form, in the nature of its hip and
hindlimb. *Lagerpeton*, the "crawling rabbit" is even
more pterosaur-like, and *Eoraptor* begins to show
more features of dinosaurs, including the reduced
calcaneum, more open hip socket, etc., etc..
Incidentally, I am more of the opinion favored by
Padian et al. 1995, such that Eo falls outside of
Dinosauria or if a dino, outside of any other group of
dino, but don't quote me on that. It just doesn't
_look_ like a dinosaur.

  (And I hope I am not offending you, Matt, but do
appologize for any impression my comments on how
"untrue" you may have been.)


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
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