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Re: Revised Ornithischian Classification

In a message dated 8/18/01 3:10:58 PM Pacific Daylight Time,
kinman@hotmail.com writes:

     I finally decided to update my classification of Ornithischiformes.  

Like Pete, I must object to the use of the term "Ornithischiformes".  Though
you say you are aiming for stability and consistency, you use a system that
promotes neither.

One major change is a return to a more inclusive Family
Hypsilophodontidae---the paraphyly of that mess is better handled at
level, and I break that family down to show one possible topology (although
it remains very unsettled):

[formatting altered slightly for clarity]

  1  Pisanosauridae
  2  Lesothosauridae
  3  A  Scutellosauridae
      B  Ankylosauridae
  4  A  Plesion _Emausaurus_
      B  Stegosauridae
  5  Plesion _Echinodon_
  6  Thescelosauridae
  7  Plesion _Agilisaurus_
  8  A  Heterodontosauridae
      B  Stenopelicidae
      C  Pachycephalosauridae
      D  Chaoyangsauridae
      E  Psittacosauridae
      F  Protoceratopsidae
         _a_ Ceratopsidae
  9  Plesion _Bugenasaura_
  ?  Plesion _Jeholosaurus_
 10  Hypsilophodontidae
          1  A  Plesion "Y." multidens
              B  Othnielia (incl. Drinker)
              C  Zephyrosaurus
              D  Orodromeus
          2  Hypsilophodon
          3  Parksosaurus
          ?  Gasparinisaura
          4  Rhabdodon
          ?  Yandusaurus
          5  Tenontosaurus
          6  Muttaburrasaurus
          7  {{Dryosauridae to
              Hadrosauridae}} (dryomorphs)
_1_  Dryosauridae
 2   Camptosauridae
 3   Iguanodontidae
_a_  Hadrosauridae
...Constructive criticism is welcome.

OK, here goes...

Why recognize a separate family for the poorly known _Stenopelix_ and not for
the well known and obviously primitive (for a stegosaur) _Huayangosaurus_?

Why recognize four families of ceratop(s)ians but not the four long-standing
and reasonably well-defined families of Ankylosauria?

Why formally recognize (as node 8) the relatively weakly supported
Marginocephalia rather than the better-supported Pachycephalosauria and

Why do you sink _Drinker_ into _Othnielia_?

Finally, why is the above formulation of "Hypsilophodontidae" any better then
the following:

 10  Euornithopoda (or whatever)
         1  A  Plesion "Y." multidens
             B  Othnielia (incl. Drinker)
             C  Zephyrosaurus
             D  Orodromeus
         2  Hypsilophodon
         3  Parksosaurus
         ?  Gasparinisaura
         4  Rhabdodon
         ?  Yandusaurus
         5  Tenontosaurus
         6  Muttaburrasaurus
         7  Dryomorpha
             A  Dryosauridae
             B  Camptosauridae
             C  "Iguanodontidae"
             D  Hadrosauridae

The above avoids entirely the (manifestly false) implication that the various
"hypsilophodontids" are more closely related to each other than any is to the
dryomorphs, and it doesn't depend on order of listing (or indeed any sort of
written list) to portray relative phylogenetic proximity.

--Nick P.