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Re: Latest K dinosaurian diversity trends

----- Original Message ----

From: "Harris, Jerald" <jharris@dixie.edu>

>>you can split the only 
North American Late Maastrichtian hadrosaurid (Edmontosaurus) into 3 taxa if 
you like, but it's still only the one clade, whereas in the Campanian we had 
multiple clades (3-4 hadrosaurines, 3-4 lambeosaurines). So diversity is just 
modified by a multiplier depending on whether you are a splitter or not.

 >   This doesn't make any sense.  Using this same logic (using clades, rather 
than species, to define diversity), one could say that there's only one clade 
present in the Late Maastrichtian terrestrial gnathostome fauna: Gnathostomata. 
Really low diversity, that.  Or among arthropods, one could say that there's 
only Hexapoda.

Yes, I'm not sure I have the words as to how to put this properly. Maybe this 
works: There is less morphological diversity among late Maastrichtian dinosaurs 
compared to Late Campanian dinosaurs. Whether or not you split the taxa into 
multiple species does not alter this. I would say that the low morphological 
variation is probably reflective of true taxonomic diversity, and that most of 
the described taxonomic variation is actually ontogenetic or stratigraphic, 
(which are both testable hypotheses and not merely individual judgement calls). 
I'd love to go into further details of species in the Hell Creek, but its other 
people's (in progress) research.