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"Ornithischia" status




Adam and George,
Perhaps I should reiterate my main point. The bigger question is whether Ornithischia has any "strong" synapomorphies. Is this taxon any more secure than Ornithodira (which is apparently being gradually abandoned by many).
I think this Massospondylus question should be looked into, and if it is a pathology, so be it. But then again perhaps there are other sauropodomorphs that have been found with possible pendant fourth trochanters, and they have been explained away one by one as pathologies or freaks just because they didn't fit in with the ornithischian paradigm.
Either way, the larger question remains of how strong the putative ornithischian synapomorphies really are, and that what is happening to Ornithodira could potentially happen to Ornithischia as well.
A predentary bone in a Cretaceous bird doesn't mean I am suggesting that birds evolved from ornithischians. On the contrary, it merely raises the question of how strong a synapomorphy the predentary really is. It also strengthens my interest in George's alternative placement of Pisanosauridae in or near marginocephalians.
I have always recognized ornithischians as a holophyletic group, and am not suggesting it be abandoned (that is the last thing I want). However, I still find all of this very troubling, and Ornithischia's holophyly needs to be looked at with skeptical eyes. If it passes inspection, all the better.
------Ken
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From: Dinogeorge@aol.com
Reply-To: Dinogeorge@aol.com
To: dinosaur@usc.edu
Subject: Re: Phytodinosauria status
Date: Mon, 18 Jun 2001 04:10:05 EDT

In a message dated 6/18/01 2:06:50 AM EST, Adam.Yates@bristol.ac.uk writes:

<< Just a word about the pendant fourth trochanter in Massospondylus. George
has used it as a possible synapomorphy between the Ornithischia and
Massospondylidae but it is only present in one individual of Massospondylus!
There are dozens of other femora all of which have the typical non-pendant
shape. No other members of the Massospondylidae have one either (I include
Lufengosaurus, Yunnanosaurus, Jinshanosaurus and probably Coloradisaurus -
there is an undescribed postcranial skeleton of this guy). I think that the
one specimen that does have it is a pathologic individual (a bony lump
growing on the ventral corner of the 4th trochanter perhaps where the
caudofemoralis had been torn off at some point in its life). >>


I got the impression that Cooper had more than this, but unfortunately my
copy of his big paper is buried and I can't check it. If this is true, then
certainly that pendant massospondylid fourth trochanter is pathological and
taxonomically useless. But I think he may have used this character when he
set up Ornithischiformes. It has been years since I've looked at this stuff.


On another track, I think Massospondylidae right now includes only
Massospondylus. Lufengosaurus and Coloradisaurus are good plateosaurids, not
massospondylids; and Yunnanosaurus and Jingshanosaurus are good
yunnanosaurids. So if they didn't have pendant 4th trochanters, it's not
particularly relevant. I wouldn't consider ornithischians and plateosaurids
or yunnanosaurids particularly closely related.
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