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Re: New ankylosaur from Liaoning



David Elliott (dalelemu@hotmail.com) wrote:

<<<Not quite a horny plate, but it has adaptations that imply it's a
bit more cursorial than the average ankylosaurian>>>

I wrote:

<<One thing the proportions of *Liaoningosaurus* and *Minmi* and
their belly armor do not show is cursorial or sub-cursorial
inclinations ... these animals are mediportal.>>

and David Elliot replies:

<I think Ralph Molnar suggested that the paravertebrae sported by
*Minmi* may have been there to support the belly armour while
running, (i've read also that *Minmi*'s limb proportions in the
Marathon Station specimen supported the idea of it running) so that
was kind of what i was getting at -- using the word "cursorial" was
probably a bit much hehe...

Did *Liaoningosaurus* or any polacanthid have something similar to
*Minmi*'s paravertebrae to maybe carry the weight of armour on it's
underside?>

  We seem to be to have been confusing the utility of the word
"cursorial" -- unless I'm really confused. Cursorial is applied to
animals that switch through a variety of gaits, run on the toes,
etc., and have longer lower limb proportions than upper limb or
pelvic/limb ratios. This leads power to the running ability.
Cursoriality is not synonymous with running. Humans are semicursorial
or medioportal, for instance, I thought I even heard it suggested we
can be classified as graviportal (having columner limbs, typical gait
is the walk, longer upper limbs with much shorter pes than femur and
even sometimes pelvic ratios...). A typical mediportal animal is the
rhinoceros, and this animal can be considered a good analogue to most
quadrupedal ornithischians in general concept (not columnar limbs,
narrow gait range [walk and run], limbs held in permanent flexure,
long or average limb ratios, pes short but not super abbreviated).
Including *Minmi*.

  [there may be error in my definitions for gravi- and mediportality,
as well as cursoriality]

  The issue of the paravertebrae is a unique one, but these seem to
serve as braces in dorsoflexion, preventing lateral flexure, etc. and
made the back rigid; they are present only in the type specimen of
*Minmi paravertebrata* and *Minmi* sp., the Marathon Crossing
specimen, and do not seem analogous to epaxial tendons (they are true
dermal bones?). A running quadruped requires a flexible back for
turning control and braking without plowing into the earth to stop.

  As for limb proportions, *Minmi* and *Liaoningosaurus* both have
relatively long tibiae, and metatarsals, intermediate between
ankylosaurs proper and scelidosaurs, indicative of a transistory
nature. Other statements must wait until Mickey is done with his
report, I don't want to be one to steal thunder :)

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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