Re: The Mystery of *Echinodon*

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

Ken Kinman (kinman@hotmail.com) wrote:

<I agree, but other genera also seem to be in this same small taxonomic area of 
divergence,
especially Jeholosaurus and perhaps Agilisaurus.
  Are Echinodon and Jeholosaurus enough alike that Echinodon could be a 
stem-thyreophoran and
Jeholosaurus a stem-cerapodan, both of which branched off soon after the 
thyreophoran-cerapodan
split? Or perhaps Echinodon is on the cerapodan stem, followed by Jeholosaurus 
(or vice versa?). 
Either way (or with Echinodon preceding the split) could Jeholosaurus be viewed 
as a sort of
intermediate form between Echinodon and Agilisaurus?
  Or does incompleteness for the fossil material and/or homoplasy make such 
questions impossible
to answer at this time?>

  At this time, without having been able to study the paper in question, I 
would take Pete
Buchholz' comments on *Jeholosaurus* over mine. I have only seen the figures, 
and there is much
more to the skeletons than skulls, but this information is not available to me. 
So I waive
discussion until I am better informed.

  My study indicates already that there seems to be a strict set of variation 
at the diverging
basal ornithischian nodes

--+--Lesothosaurus
  `--Genasauria
      |--Thyreophora
      `--Cerapoda
          |--Marginocephalia
          `--Ornithopoda

  Here, *Echinodon* could be at any stem or node in this tree. The teeth and 
jaws between
*Lesothosaurus*, *Scutellosaurus*, *Agilisaurus*, *Thescelosaurus*, and 
*Echinodon* are all very
similar to one another, only *Hypsilophodon*, *Scelidosaurus*, *Pisanosaurus*, 
and
*Heterodontosaurus* appear to indicate an exclusion from any higher or lower 
placement than what I
offer. *Scutellosaurus*, as before, offers me the closest paradigm to the teeth 
in *Echinodon*,
having nothing to do with supposed dermal armor in the beds with it.

  *Jeholosaurus*, in the analyses that Mickey and Pete performed, tended to 
move up and down a few
nodes, but gravitated around the Cerapoda/Ornithopoda group, so it is likely 
that based on that,
it may very well be a cerapodan. My placement for *Thescelosaurus* has always 
been at the base,
but I will leave it to Pete to place it higher, as he is more familiar with 
this animal than I am.
*Agilisaurus* IS a basal form, quite a primitive animal and even a paraphyletic 
concept for
"Hypsilophodontidae" would not do the taxon justice. The only taxa I would 
retain in a possibly
paraphyletic "Hypsilophodontidae" would be *Zephyrosaurus*, *Othneilia*, and 
*Hypsilophodon*, and
allies, with other taxa (*Parksosaurus*, *Agilisaurus*, *Thescelosaurus* etc. 
out of the mix based
on advanced or basal characteristics [respectively] that only mislead the 
septuply [or so...]
paraphyletic grouping adopted). Presently, I am aware of very few (if 
any)workers who now use
"Hypsilophodontidae" to refer to anything but a useless wastebasket, as the 
contents vary too much
on a spectrum to be remotely similar...


=====
Jaime A. Headden

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

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