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RE: Diagnostic Material
Tom Holtz wrote:
<It is fairly straight forward, but sadly (like much in this world) a relative
term subject to change with new information.
Diagnostic = possesses traits sufficient to distinguish it from other taxa
known at the time of the initial write up of the specimen and coining of the
This definition is problematic. Any time a new taxon is described for a given
clade, the relative diagnosticity (or whatever) of the material of an earlier
named taxon reduces, such that it becomes _less diagnostic_ for its own taxon.
Extending this through time, we'd expect even a "new" fossil to be so limited
in its uniqueness that the material could be complete and still nondiagnostic.
The term as I've seen it used also refers to the capability of determining
differentiable features, regardless of whether they are autapomorphic, so long
as they are apomorphic. This is how Paul and Carpenter use it, but they extend
this definition (without using any) to the suite of material they discuss. So
the argument seems to also suggest that a certain amount of material cannot be
diagnostic, regardless of the associated viability of that material.
For example, several aetosaurs are diagnosed originally on the basis of a few
bits of armor, and despite decades of research, this material remains unique in
some apomorphies to permit the material to be diagnostic (aetosaur armor being
very differentiable to a certain degree, which some have split to the specific
level). It has also been used to support sauropod dinosaurs, in that there are
more than a few named on the basis of only a dorsal vertebra, portions thereof,
or a series of a few dorsal vertebrae.
If we extend the argument of Paul and Carpenter to a percentage based value
to how much of a given amount of material is diagnostic, then we can assert
that each of these singular elements makes up, say, a percentage of the
skeleton (and as they can be coded for apomorphies, we can use Mannion and
Upchurch's recent CSM to quantify the value for the specimen. If I were to
acquire a humerus of a theropod dinosaur, and I can split the humerus into
about 45 discrete apomorphic values (and I can) half of a humerus should
reasonably be supportive of half that many characters to score, making its
comparable value relatively higher than a phalanx (unless I can apply more
apomorphies to a phalanx). This would support high values for some bones, lower
for some, but it becomes compounding when you have scattered elements of a
skeleton, and thus the comprehensiveness of the material increases.
It is likely not arguable that YPM 1930 is diagnostic under the definition of
lacking autapomorphies, but it is hardly true that it lacks apomorphies, and as
such, that it can be determined as likely belonging to *Allosaurus fragilis*,
regardless of whether it can be applied to *Allosaurus* sp. vide Chure, one can
say the material is diagnostic (it can be applied to *Allosaurus*. Were it crap
without any differentiable qualities, then I'd say it was essentially
nondiagnostic, but such material you only find in things LIKE crap, sensu
dinosaur dung containing bone bits.
<The problem is that greater numbers of taxa (and/or variation within taxa) are
discovered, what was once a unique set of traits may be found to be much more
We all know we'll eventually discover all potential species, or at least
until people start oversplitting out of boredom.
The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with