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Re: Dinosauria---Rejected Name?



George Olshevsky (Dinogeorge@aol.com) wrote:

<It sounds good, but I'm pretty sure that this way of defining clades
makes it theoretically impossible to demonstrate that any taxa other than
the anchor taxa are included in or excluded from a clade. You will need
characters one way or another, so you might as well put them right into
your definitions, not just your diagnoses.>

  Implicit in the formula is "the most recent common ancestor", and thus
all forms that existed between the anchors and that ancestor, as well as
"and all descendants of that ancestor," and thus those anchors and any
_possible_ descendants are included. This is without and character
reference. A diagnosis will always change with new content changes, the
inclusion or exclusion of species, and thus is more plastic. To _set_ such
a diagnosis is erroneous in practice, since perhaps only one taxon could
reliably be refered to the group. *Lambeosaurus* can thus only include the
type of *L. lambei*.... Individual variation be damned (and yes, it can be
significant enough between individuals to vary the apparent diagnostic
features of a taxon, take cranial variation in *Tyrannosaurus rex* and
*Corythosaurus casuarius*, for example).


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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