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A few taxonomic questions (resend)



Hi,

I am currently reviewing my  old dinosaur species list, and have a few points 
I would like to shed light on.  From a general point of view, am I right to 
believe that a nomen dubium cannot  be referred to another species? 

For example, among the first dinos in  any list (in alphabetical order of 
course) comes Aetonyx palustris (Broom 1911),  which is almost always 
considered 
a junior synonym of Massospondylus carinatus.  However, in TD 2nd Edition, 
Aetonyx is listed separately as a nomen dubium. I  suppose that if the material 
is not diagnostic, it is not possible to assign it  to any particular species, 
even if it seems extremely probable that it belongs  to M. carinatus. Have I 
got it right? And by the way, how diagnostic is the  actual Aetonyx material?

And then comes the infamous Agathaumas, and with  it some questions for 
ceratopsian fans here... And I don't seem to be able to  determine exactly how 
many 
species have actually been named. There's no problem  with A. sylvestris 
(Cope 1872), the type species. No problem either with A.  flabellatus, 
originally 
Triceratops flabellatus (Marsh 1890), referred to  Agathaumas by Scott (1900) 
and now included in Triceratops horridus, or with A.  prorsus, originally 
Triceratops prorsus (Marsh 1890), referred to Agathaumas by  Lydekker (1893) 
and 
now again T. prorsus.

But...what about A. milo (Cope  1874)? I've seen it listed as a junior 
synonym of Thespesius occidentalis on the  net, while TD considers it a junior 
synonym of Edmontosaurus regalis. But isn't  it a nomen dubium? In that case, 
shouldn't it keep being A. milo?

Then  comes Agathaumas monoclonius Breithaupt 1994, which I can't see listed 
anywhere  except on the Dino Russ's Lair website. What is it? And last but not 
least, the  same website lists an Agathaumas sphenocerus Cope 1890, which 
appears to be the  same as Monoclonius sphenocerus Cope 1889. Did E. D. Cope 
reassign the species  one year after describing it? Does the combination A. 
sphenocerus actually  exist?

Thanks in advance,

Félix Landry