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Re: [dinosaur] Ceratopsid (Centrosaurinae: Nasutoceratopsini) from Oldman Formation of Alberta (free pdf)
For what it's worth, I think Avaceratops is valid and diagnostic. It sure isn't
Nasutoceratops. Some of the supposed autapomorphies and other seemingly trivial
characters being used to diagnose taxa are indeed questionable, but I'm not
convinced ceratopsids are overdivided. Dinosaurs were not mammals.
--------------------------------------------
On Wed, 12/14/16, Mickey Mortimer <mickey_mortimer111@msn.com> wrote:
Subject: Re: [dinosaur] Ceratopsid (Centrosaurinae: Nasutoceratopsini) from
Oldman Formation of Alberta (free pdf)
To: "DML" <dinosaur-l@usc.edu>
Date: Wednesday, December 14, 2016, 12:47 AM
I was going to comment on this myself, but of course in
the well-worn opposite direction. I think the current
state of ceratopsid nomenclature is unrealistically
oversplit, where a few differences or million years are
considered enough to doubt conspecificity
(ditto for Tschopp's Morrison diplodocids). Compare
this to theropods, where there are tons of differences
between e.g. Tyrannosaurus rex specimens, which are known
from the lower and upper parts of the Hell Creek Formation,
as well as the Scollard, Denver,
Lance, Frenchman, etc. Formations all over the continent.
I would call Ryan et al.'s Nasutoceratopsini Avaceratops.
Notably, Ryan et al. are confusingly contradictory in
their discussion of Avaceratops. They first state the
holotype specimen "ANSP 15800 has three unambiguous
autapomorphies: Ch 36 (jugal infratemporal process, 1>0;
absent), Ch 49 (parietal, sharp median
crest, 1>0; absent), and Ch 53 (marginal dermal
ossifications on parietal and squamosal, 1>0;
absent)", but then they say "it is currently
difficult to diagnose Avaceratops because it appears to lack
autapomorphies or any unique combination of
characters."
Their conclusion is "As a result, Avaceratops is
represented only by the type specimen
(ANSP 15800). This immature individual exhibits no
undisputed apomorphies, rendering a diagnosis of the taxon
problematic. Nevertheless, the specimen cannot be attributed
to any other known centrosaurine, and so the genus cannot be
synonymized or declared a nomen dubium."
Which is it? If it has no autapomorphies or character
combinations considered taxonomically valid, then it _could_
be synonymized with Nasutoceratops or alternatively declared
a nomen dubium if it also couldn't be distinguished from
other diagnostic nasutoceratopsin
genera (e.g. maybe the Malta taxon once it's named).
But if it can't be attributed to any other known taxon,
then that must be based evidence which would thus form the
diagnosis.
Finally, why do you continue the myth that ICZN-covered taxa
like Ceratopsidae are affected by the eponymous genus'
diagnosability? Haven't I put enough stakes into
Wilson and Upchurch's baseless assertion this is the
case?
Mickey Mortimer