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Re: Heterodontosaurid with protofeathers



On Thu, Mar 19, 2009 at 3:50 PM, Tim Williams <tijawi@yahoo.com> wrote:
>
> No, I wasn't saying that Avifilopluma should be converted to a node- or 
> stem-based clade. ÂI was only making the point (said many times before) that 
> having a clade founded on an integument-based apomorphy (as Avifilopluma is) 
> is fraught with danger, given the vagaries of the fossil record.

Well, if shifting or uncertain content = "danger", then phylogenetic
nomenclature may not be your cup of tea, anyway.

I mean, certainly this is an extreme example, but it's still an
interesting clade, no matter what it turns out to contain.

> Thanks - yes, that's the precise issue I was getting at. ÂIn the unlikely 
> event that either saurischians or ornithischians are found to be closer to 
> crocodylians, then under the current definition (_Triceratops_ + _Passer_)

Anchoring the definition of _Dinosauria_ on _Passer_ is a bad idea.
The draft PhyloCode explicitly recommends against it:

Recommendation 11A. Definitions of converted clade names should be
stated in a way that attempts to capture the spirit of traditional use
to the degree that it is consistent with the contemporary concept of
monophyly. Consequently, they should not necessitate, though they may
allow, the inclusion of subtaxa that have traditionally been excluded
from the taxon, as well as the exclusion of subtaxa that have
traditionally been included in the taxon. To accomplish this goal,
internal specifiers of converted clade names should be chosen from
among the set of taxa that have been considered to form part of a
taxon under traditional ideas about the composition of that taxon, and
they should not include members of subtaxa that have traditionally
been considered not to be part of the taxon.

Example 1. The name _Dinosauria_ 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 would force birds to be dinosaurs, thus
trivializing the question of whether birds are dinosaurs. Instead,
internal specifiers should be chosen from among taxa that have
traditionally been considered dinosaurs; e.g., _Megalosaurus
bucklandii_ von Meyer 1832, _Iguanodon bernissartensis_ Boulenger in
Beneden 1881, and _Hylaeosaurus armatus_ Mantell 1833.

<http://www.ohio.edu/phylocode/art11.html#rec11a>

That said, your example still holds, but you wouldn't have to give
_Dinosauria_ a qualifying clause if you just established that the name
_Archosauria_ has priority for Clade(_Crocodylus niloticus_ + _Vultur
gryphus_) (or whatever).
-- 
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California