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Re: preliminary ornithischian classification

Alessandro and George,
WOW Alessandro, you convinced me!!! Have now placed Heterodontosauridae (spelled correctly this time) in the marginocephalian clade (clade 4 below). If somebody thinks it should be changed back, it would take a list of characters at least as impressive as the one Alessandro gave.
Thank you George for your feedback as well. I changed the plesion to a family Pisanosauridae.
The only really "BIG" question in my mind now is whether or not Ankylosauridae and Stegosauridae (both sensu lato here) are really sister groups or not. Apparently some workers think Stegosaurs are sister group to cerapodans (in a clade excluding ankylosaurs). I have no strong opinion one way or the other at the present.
I went ahead and put in a plesion for Thescelosaurus below as well. By the way, are there any major objections to placing Iguanodon as a primitive hadrosauridae? I didn't see any need to maintain that as a small family of its own (but I have this dreadful feeling someone is going to tell me Iguanodontidae has priority).
Thanks for the help, Ken Kinman
ORDER ORNITHISCHIFORMES (ornithischians; predentates)

       1  Pisanosauridae
       2  Fabrosauridae
      3A  Ankylosauridae
       B  Stegosauridae
      4A  Heterodontosauridae
       B  Pachycephalosauridae
       C  Psittacosauridae
       D  Protoceratopsidae
      _a_ Ceratopsidae
       5  Plesion _Thescelosaurus_
       6  Zephyrosauridae
       B  Othnieliidae
       7  Hypsilophodontidae
       8  Camptosauridae (incl. dryosaurids)
      _a_ Hadrosauridae (incl. Iguanodon)
Alessandro wrote:
A little comments in regard to 5 Heterodontidae: I think that it's time to
re-evaluated the sistematic position of Heterodontosaurids as basal
(EuOrnithopoda sensu Sereno 1986), infact, there are evidence for which
Heterodontosaurids must be considered Marginocephalia. I also think that
it's time to reconsidered the diagnostic characters of the
Heterodontosaurids proposed by Weishampel and Witmer (1990) expecially:
(1) The presence of caniniform teeth in the premaxilla and in the dentary,
infact the caniniform teeth are present in Heterodontosaurids
(Heterodontosaurus, Lycorhinus, and Abrictosaurus (specimen UCL A.100)),
Pachycephalosauria (Wannanosaurus, Goyocephale, ?Homalocephale, Stegoceras,
and Prenocephale) and Ceratopsia (Leptoceratops sp. (specimen USNM 13863
(Gilmore 1939)), Protoceratops, Breviceratops, and ?Bagaceratops) absent in
others Ornithischia, moreover, the number of three premaxillary teeth is
found in Heterodontosaurids
(Heterodontosaurus, Lycorhinus, and Abrictosaurus) and in Pachycephalosauria
(Goyocephale, Homalocephale, Stegoceras and Prenocephale) within
Marginocephalia, in Ceratopsia there is a reduction to two premaxillary
teeth ( in others Ornithischia when present the premaxillary teeth are in
number of five, six, or seven):
(2) The chisel-shaped crowns of the cheek teeth with serrations restricted
to the uppermost third of the crowns of the Heterodontosaurids is present
also in the Ceratopsia Chaoyangsaurus youngi.
Others characters that linked Heterodontosaurids with Marginocephalia are:
(3) The lateral boss on the jugal is found in Heterodontosaurids,
Pachycephalosauria and Ceratopsia, however within Marginocephalia,
Ceratopsia possses the derived condition of the jugal boss, infact, the
jugal boss of Heterodontosaurids and Pachycephalosauria lacks the crest on
the lateral surface of the jugal (also absent in Chaoyangsaurus) present in
all the Ceratopsia, a jugal boss is also present in the Ornithopoda
Orodromeus and Zephyrosaurus, but this could be explained as convergence.
(4) The premaxillary teeth of Heterodontosaurids (Heterodontosaurus),
Pachycephalosauria (Goyocephale, Homalocephale, Stegoceras, and
Prenocephale), and Ceratopsia (Protoceratops and Breviceratops)
progressively increase in length from front to back, in others Ornithischia
the premaxillary teeth are subequal:
(5) In Heterodontosaurids there is a large diastema between the premaxillary
and maxillaty teeth, this is present also in Pachycephalosauria and
(6) The absence of an obturator process on the ischium is found in
Heterodontosaurids, Pachycephalosauria and Ceratopsia.
(7) The presacral count of 21-22 is found in Heterodontosaurids,
Pachycephalosauria, and Ceratopsia in others Ornithischia che presacral
count is at least 24.
(8) A strap-shaped scapular blade is found in Heterodontosaurids,
Pachycephalosauria (Stegoceras (UA-2)) and Ceratopsia (Protoceratops):
(9) Distal expansion of the preacetabular process of the ilium is found in
Heterodontosaurids (Heterodontosaurus), Stenopelix, Pachycephalosauria
(Goyocephale, Stegoceras, Homalocephale).

Comment are welcome

Marisa Alessandro
"Volounteer of Museo Paleontologico Cittadino, Monfalcone"
Via Achille Grandi n°18
Tel:039-0464-434658 Email amaris@tin.it
Museum Web-Page: http://www.fante.speleo.it

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