Re: Cladistic definitions of Dinosauria, Saurischia, Sauropodomorpha

[mike@miketaylor.org.uk (Mike Taylor)]

> Date: Mon, 19 Sep 2005 08:52:21 -0700
> From: "T. Michael Keesey" <keesey@gmail.com>
>
>> Are there "generally accepted" cladistic definitions of Dinosauria,
>> Saurischia and Sauropodomorpha that seem to be winning out?
> 
> [snip]

First up, Mike, thanks for these excepts and citations.  Very helpful.

But --

> * Padian and May 1993: "all descendants of the most recent common
> ancestor of birds and _Triceratops_"
> 
> * Sereno 1998: "_Triceratops_, Neornithes, their most recent common
> ancestor and all descendants"
> 
> * Kischlat 2002: [...] "the most recent common ancestor between [i.e.
> "of"] _Megalosaurus_ (a saurischian) and _Hylaeosaurus_ (an
> ornithischian), as well as all its descendants, including the birds"
> 
> * Clarke 2004: "the clade comprised of the most recent common ancestor
> of Owen's (1842) specifiers for his 'Dinosauria' (_Megalosaurus_ and
> _Iguanodon_) and all of its descendants"

Well, I am firmly in the don't-use-birds-as-anchors camp, so that
pushes Padian and May's and Sereno's definitions out the door.  That
leaves me with a choice of a non-English language definition --
unappealing -- or Julia Clarke's formulation.  The problem with that
is that Clarke in context is clearly not proposing a definition but
recognising one:

        Other previously phylogenetically defined taxon names
        are repeatedly used throughout the current document.
        To briefly summarize the usage of these names:
        ``Dinosauria'' is used as a node-based name for the
        clade comprised of the most recent common ancestor of
        Owen's (1842) specifiers for his ``Dinosauria''
        (Megalosaurus and Iguanodon) and all of its
        descendants; ``Theropoda'' (Gauthier, 1986) refers to
        Aves and all saurishian dinosaurs more closely related
        to Aves than Sauropodomorpha [...]

It's as though she just forgot the citation.

Also, I need a definition of Saurischia, which should clearly be the
stem (_Megalosaurus_ not _Iguanodon_) if we're using Dinosauria sensu
Clarke.  She doesn't mention this clade at all; surely it can't be
that no-one has ever published this definition?

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "You cannot simultaneously have mass adoption and rigor" --
         Clay Shirky.