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diagnostic characters in dino skeletons

Some quick thoughts on where the diagnostic characters in dinosaur skeletons
are to be found.

Some here have asserted that, within the family or subfamily level, the
postcranium is less informative than the cranium.  This is certainly true
within some major, large bodied, Late Cretaceous Asiamerican clades.  It is
difficult to distinguish among the tyrannosaurines, among the
centrosaurines, among the ceratopsines (aka chasmosaurines), among the
lambeosaurines, and among the hadrosaurines without skull material.

However, this pattern does not hold for other dinosaur "family rank" taxa.
Many of the features that distinguish Syntarsus from Coelophysis are
postcranial.  Almost all the diagnostic features for each ornithomimid genus
are postcranial.  The extreme, of course, are the sauropods.  Since we don't
know what the skulls of most sauropod genera look like, almost all the
features used to distinguish confamilial forms are postcranial (i.e.,
Barosaurus from Diplodocus from Apatosaurus, Brachiosaurus from Astrodon,
all the titanosaurid taxa, etc.).

So, the pattern does not hold within the non-avian dinosaurs, although it is
pretty strong within a few important, speciose taxa.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661