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Re: Defining Ornithischia (was Re:)



Mr. Peters is using a character-based definition for
Paranornithischia.  For example, Mr. Peters regards
the following characters as important in establishing
a relationship between Lotosaurus, Silesaurus and
Lesothosaurus:

1. Ventral maxilla is narrow.
2. The orbit marks the halfway point of the skull.
3. The quadrate rises vertically and is concave
posteriorly.

That is not a definition. It is a diagnosis. A definition would have to mention at least one organism.


Mr. Peters inteprets Effigia and Lotosaurus as
possessing a predentary bone,

Bizarre. *Effigia* has been described in quite some detail, so I have to assume a predentary would have been noticed. The mounted skeleton of *Lotosaurus* has no such thing (pers. obs.).


Mr. Peters also discounts the
presence of a calcaneal spur in Lotosaurus and Effigia
as a character that would disqualify these taxa as
ornthischians.

He is right about that. A single (bizarre) convergence wouldn't prove anything. It's the totality of the phylogenetically informative characters that shows them not to be dinosaurs.


David Peters does not restrict his thoughts regarding
alternative phylogenies in the Prehistoric Times
articles to ornithischians.  In issue # 80, Mr. Peters
gives us his interpretation of all of Amniota.
He states that he used 151+ taxa with 228 characters,
the matrix for which he created in MacClade and
analyzed with PAUP.

He was so kind as to send me an earlier version of the character list and something that was supposed to be a synapomorphy list. All characters were unordered, some states had bizarre definitions... and 228 characters for 151 taxa is _nothing_. I wouldn't bother publishing below 3 times as many characters as taxa.


A few of the conclusions from David Peter's effort
are:

1. Cephalerpeton is considered to be the basalmost
amniote.

That would mean it is the sister-group of Amniota, which is defined as a crown-group.