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Re: Cladistic definitions of Dinosauria, Saurischia, Sauropodomorpha



On 9/19/05, Mike Taylor <mike@miketaylor.org.uk> wrote:
> > Date: Mon, 19 Sep 2005 08:52:21 -0700
> > From: "T. Michael Keesey" <keesey@gmail.com>
> > * 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

Kischlat did also express his definition as a formula
(_Megalosaurus_+_Hylaeosaurus_), if that helps.

> -- or Julia Clarke's formulation.  The problem with that
> is that Clarke in context is clearly not proposing a definition but
> recognising one:
[...]
> It's as though she just forgot the citation.

Ah yes--good point.

I also have that Novas (1992) defined _Eudinosauria_ as "the common
ancestor of Saurischia and Ornithischia and all of its descendants",
which suggests he had a more inclusive definition for _Dinosauria_,
but, unfortunately, I don't have the paper itself. (This is the one I
was trying to think of earlier. I suppose it might also suggest that
he didn't, at the time, think the term "Dinosauria" should be expanded
to include _Aves_, and so erected a new name for such a clade, but I
really don't know.)

> 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?

Not quite, but there are some that don't use birds:

* Kischlat 2002: "a ancestralidade de _Allosaurus_ e sua descendência
(e.g., aves), não compartilhada por _Stegosaurus_ (um ornitísquio)"

English translation (mine): "the ancestry [ancestor?] of _Allosaurus_
and its descendants (e.g. birds), not shared with _Stegosaurus_ (an
ornithischian)"

formula: _Allosaurus_¬_Stegosaurus_ (that's the logical "not" symbol)

* Holtz & Osmólska 2004: "all dinosaurs more closely related to
_Tyrannosaurus_ than to _Triceratops_"

* Langer 2004: "all dinosaurs that share a more recent common ancestor
with _Allosaurus_ than with _Stegosaurus_"

Morrison or Lance--take your pick.

—Mike Keesey