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

["Matthew Bonnan" <mbonnan@hotmail.com>]

Rats.  I sent 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. =) =(

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.

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.

In my original, now vanished, posting, I described this and other things in 
some detail.  I also encouraged interested list members to read the 
following articles:

Paul Sereno and Andrea Arcucci. 1994. Dinosaurian precursors from the Middle 
Triassic of Argentina: Marasuchus lilloensis, gen. nov. Journal of 
Vertebrate Paleontology, 14(1): 53-73.

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.

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 and 
is longer lateromedially than anteroposteriorly.  Again, this allows motions 
back and forth, but limits side-to-side motions considerably.

For those interested in that wild-card Megalancosaurus that get's thrown 
very often into conversations of non-dino/bird origins, you may be 
interested in this article, also in the same issue:

Silvio Renesto. 1994. Megalancosaurus, a possibly arboreal archosauromorph 
(Reptilia) from the Upper Triassic of northern Italy. Journal of Vertebrate 
Paleontology, 14(1): 38-52.

Hope this helps,
Matt Bonnan

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com