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Re: HYPSILOPHODONT MONOPHYLY AND THE ORIGIN OF BIRDS



Peter Buchholz wrote:

<Aside from Darren's (true) characters of "small" and
"bipedal" they actually find some codible characters. 
Among them are:
 
 1) absence of ridges that culminate in marginal
denticles
 2) presence of a cingulum
 3) ossification of sternal segments of the cranial
dorsal ribs
 4) rod-shaped prepubis

 and for the clade that excludes Thescelosaurus

 5) paired frontals wider than long
 6) long axis and base of the braincase at
approximately 35 degree angle.>

  Okay, I'll bite:

  Only pelvic characters included for now....

  Hypsilophodontidae, were it unique, might also be
  distinguished by:
    1. ischium curves toward pubis distally, sigmoid
       lateral aspect; in A. louderbacki, O. rex, Y.
       multidens, S. valdensis, H. foxii, and bunches
       of other "higher" ornithopods.
    2. no distal expansion to prepubic process of
       pubis; in D. nisti, O. rex, A. louderbacki, Y.
       multidens, and H. foxii.

  Excluding *Thescelosaurus,* a distal expansion of
the ischium is also observed, as in *Lesothosaurus*
and *Heterodontosaurus*.

 Otherwise, some interesting features:

  == {*Drinker* + *Othnielia*}
    3. prepubic process of pubis tapers to a point;
    4. horizontal dorsal margin on ilium in lateral
       view;
    5. prepubic process of pubis and anterior blade of
       ilium parallel to each other and the
       longitudinal plane of the sacrum;

  == {*Agilisaurus* + *"Y." multidens*}
    6. squared-off posterior blade of ilium,
vertically 
       oriented;

  == {*Thescelosaurus* + *Gasparinisaura*}
    7. distal end of prepubic process of pubis
       expanded;

  == {*Gasparinisaura* + *Agilisaurus*}
    8. prepubic process of pubis and anterior blade of
       ilium converge [but do not touch];

  == {*Muttaburrasaurus* + *Tenontosaurus* +
      *Thescelosaurus* + Dryomorpha}
    9. prepubic process of pubis declines from
       acetabular margin;

  == {*Muttaburasaurus* + Styracosterna}
    10. no neck on the ischiadic pedicle for the
ilium;
    11. ilium strongly arched, highest anterior to the
        apex of the acetabulum;

  == {*Thescelosaurus* + *Muttaburrasaurus* +
      *Hypsilophodon* + Dryomorpha}
    12. obturator foramen on pubis open posteriorly;
        closed in D. nisti, A. louderbacki, G.
        cincosaltensis, "Y." multidens, and O. rex.

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

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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