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Re: Ceratosauria vs. Neotheropoda?

On Fri, Nov 20, 2009 at 2:59 PM, Augusto Haro <augustoharo@gmail.com> wrote:
> Question for people who know about Phylocode:
> Langer et al. (2009) pointed out that the oldest available
> phylogenetic definition of Ceratosauria is synonymous with
> Neotheropoda. They point out that Rowe and Gauthier (1990) defined
> Ceratosauria as a node-based taxon this way: "We employ the name
> Ceratosauria for the group including Ceratosaurus nasicornis,
> Dilophosaurus wetherilli, Liliensternus liliensterni, Coelophysis
> bauri, Syntarsus rhodesiensis, Syntarsus kayentakatae, Segisaurus
> halli, Sarcosaurus woodi , and all other taxa stemming from their most
> recent common ancestor".

Given current topologies, this is not likely to coincide even closely
with the traditional meaning of the name "Ceratosauria". If this
definition had been published under the PhyloCode, it would likely
qualify for an emendation (see Article 15), either trimming some of
the specifiers to yield a clade that does not include avians, etc., or
adding a qualifying clause nullifying the definition if it includes
avians, etc. Fortunately, it was not defined under the PhyloCode,
since the PhyloCode hasn't been enacted yet, so there is time to
formulate a definition that is more stable and more continuous with
the literature (which is, after all, part of the purpose of having a
code in the first place). Something along the lines of, "everything
sharing more recent ancestry with Ceratosaurus nasicornis (Marsh 1884)
than with [insert tetanuran species here]," would probably work.

Incidentally, Sereno's (1998, 2003) definition of "Neotheropoda"
pretty much explicitly contradicts the original usage by including
_Coelophysis_ as a specifier. In the original usage (Bakker 1986),
"podokesaurids" (=coelophysids) were explicitly excluded. Therefore,
Padian & al.'s (1999) definition (which uses _Ceratosaurus_ instead)
is preferable as a basis.
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California