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Re: Cladistic definitions of Dinosauria, Saurischia, Sauropodomorpha
The Draft Committee is comparing apples and oranges when they speak of
both Owen's 1842 name and the later cladistic definitions, and their
opinion appears somewhat petty. I *do* understand their reasons (they
are trying to prevent "activist clade naming", where someone defines a
clade in order to make a point _a priori_). But I think the Committee
should have used a different example to make their point. John Ostrom
and later, J. Gauthier, solidified the position of birds as dinosaurs
years before Padian and May's definition appeared in print.
I like Padian and May's (1993) definition, not just because it appears to
have date priority(?) over all other clade definitions, but also because
it is "edgy" and current.
On Mon, 19 Sep 2005 08:52:21 -0700 "T. Michael Keesey" <email@example.com>
> On 9/19/05, Mike Taylor <firstname.lastname@example.org> wrote:
> > Are there "generally accepted" cladistic definitions of
> > Saurischia and Sauropodomorpha that seem to be winning out? As an
> > example, within Sauropoda, it seems clear that Wilson and Sereno's
> > 1998 definition of Diplodocoidea as (_Diplodocus_ not
> > _Saltasaurus_) is now used more or less universally. But I know
> > that there are various competing candidate anchors for Dinosauria
> > (e.g. _Triceratops_ and _Passer_, _Megalosaurus_ and _Iguanodon_)
> > and I wondered which way the wind is now blowing.
> This is the original diagnosis:
> * Owen 1842 (abridged): "This group ... is characterized by a large
> sacrum composed of five ankylosed vertebræ of unusual construction
> ; by broad ... coracoids and long and slender clavicles, whereby
> Crocodilian characters of the vertebral column are combined with a
> Lacertian type of the pectoral arch; the dental organs also exhibit
> the same transitional or annectent characters.... The bones of the
> extremities ... are provided with large medullary cavities and with
> well-developed and unusual processes, and are terminated by
> metacarpal, metatarsal, and phalangeal bones."
> This is the original composition:
> * Owen 1842: "Of this tribe [Dinosauria] the principal and
> best-established genera are the _Megalosaurus_, the _Hylæosaurus_
> [sic], and the _Iguanodon_."
> These are the published definitions:
> * 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: "o ancestral comum mais recente entre Megalosaurus
> (um saurísquio) e Hylaeosaurus (um ornitísquio), assim como todos os
> seus descendentes, incluindo as aves"
> English translation: "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
> [my translation, ably assisted by Babelfish]"
> abbreviated formula: "Dinosauria=_Megalosaurus_+_Hylaeosaurus_"
> * Clarke 2004: "the clade comprised of the most recent common
> of Owen's (1842) specifiers for his 'Dinosauria' (_Megalosaurus_ and
> _Iguanodon_) and all of its descendants"
> And here is PhyloCode's comment about what the definition should be
> * Cantino and de Queiroz, 2003 [Internet only]: "The name
> was coined by Owen for the taxa _Megalosaurus_, _Iguanodon_, and
> _Hylaeosaurus_, and traditionally the taxon designated by that name
> has included these and certain other non-volant reptiles. It has not
> traditionally included birds. Although birds are now considered part
> of the dinosaur clade, the name _Dinosauria_ should not be defined
> using any bird species as internal specifiers. Such a definition
> force birds to be dinosaurs, thus trivializing the question of
> birds are dinosaurs. Instead, internal specifiers should be chosen
> from among taxa that have traditionally been considered dinosaurs;
> e.g., _Megalosaurus bucklandi_ von Meyer 1832, _Iguanodon
> bernissartensis_ Boulenger in Beneden 1881, and _Hylaeosaurus
> Mantell 1833."
> Padian in Currie and Padian 1997 mentions a personal communication
> from T. R. Holtz, suggesting usage of _Megalosaurus_ and _Iguanodon_
> as internal specifiers, but follows priority, settling on the
> definition from Padian and May 1993.
> Note that all of these definitions yield the same clade under all
> published phylogenies of the past couple of decades. Hence, I
> most researchers don't feel the need to pick one, so there is no
> I'd also like to note that the disagreement between Kischlat and
> Holtz/Clarke over which of Owen's ornithischians to use in the
> definitions (_Hylaeosaurus_, the first one listed in Owen 1842, and
> _Iguanodon_, the first one published, and better known of the two)
> could be easily remedied, without affecting the taxon's application,
> by including both of them. This would also pay better homage to Owen,
> I think: the last common ancestor of _Megalosaurus bucklandi_ von
> Meyer 1832, _Hylaeosaurus armatus_ Mantell 1833, and _Iguanodon
> bernissartensis_ Boulenger in Beneden 1881, plus all of descendants
> thereof. Unfortunately, I don't think anything like this has been
> published. (Clarke comes close, but failes to mention
> ?Mike Keesey
> P.S. I don't actually have all of these papers in front of me (just
> Kischlat 2002 and Currie and Padian 1997), just notes, so you may
> to double-check the original sources.
> P.P.S. I could swear there was an early definition of _Dinosauria_
> that had some herrerasaurid[s] (or possibly _Herrerasauridae_
> as an internal specifier, but all I can find is a mention that
> Gauthier (1986) states a definition like that, but clearly excludes
> _Herrerasauridae_ in his usage. I think the definition I'm thinking
> is from someone else's paper, though ... if it exists....