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RE: Ceratops (was RE: Glishades ericksoni, ...)
Mickey Mortimer wrote:
<Lots of valid taxa are based on single elements- Kemkemia, Ozraptor,
Becklespinax, Iliosuchus, Kakuru, Rapator, Unquillosaurus, Caenagnathasia,
Pneumatoraptor, Richardoestesia, Itemirus, Urbacodon, the famous
This is actually not favorable towards *Ceratops montanus* in the sense that
you argue. Simply having a taxon named on the basis of a relatively low
percentage of the skeleton does not validate the practice of naming taxa on
such a basis. Virtually all taxa named from one, or two bones, even if they are
cranial, reduces the comparability of the taxon used.
We have two ways to compare percentage of the skeleton: Valuing the total
bone mass, and subtracting the material not preserved; and valuaing the bone
preserved as though it were complete (both approaches are covered in ).
Mannion and Upchurch  add a value for sauropods where the gross number of
definable characters relative to the body region/skeleton can also be used, and
it represents a third and novel manner in which we evalutate the completeness
of a skeleton. We can use these numbers to help us determine whether a specimen
is "diagnostic," and assign a threshhold value for taxonomic nomenclature. We
don't and so far very few people have attempted to do so. Taylor  recently
valued the number of characters by which the brachiosaurs *altithorax* and
*brancai* differed, and this represents a particularly interesting starting
point from which to discuss the value of ranks in the bias of taxonomic
nomenclature (and make no mistake, there are more than just a few biases
Most of the taxa you list above are rendered difficult to associate with
others simply because of their incompleteness. You need to have particular
portions recovered in order to support these taxa generally, although in the
specific one _could_ make the argument that gross differentiation is all you
need. The problem with this argument, though, and one of the things that makes
me like the idea of making it so that all these taxa are nomina dubia and
should not be made the basis of further taxonomy is that this material is
directly differentiable only through a temporal gap in our knowledge: we will
eventually find more out there, will eventually conflate different taxa from
different formations based on some hypotheses, and will eventually merge taxa
on the basis of representing different parts of the same skeleton -- not just
the same type of organism, or taxon, but even the same original individual.
 Mannion, P. D. and Upchurch, P. 2010. Completeness metrics and the quality
of the sauropodomorph fossil record through geological and historical time.
 Taylor, M. P. 2009. A Re-evaluation of *Brachiosaurus altithorax* Riggs
1903 (Dinosauria, Sauropod) and its generic separation from *Giraffatitan
brancai* (Janensh 1914). _Journal of Vertebrate Paleontology_ 29(3):787-806.
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