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Re: PACHYRHINOSAUR LINEAGE
> I read the _Nature_ paper, and yes there were three taxa. I'm
> assuming taxon A is a species of _Styracosaurus_ (but I wondered
> about that too). Which one (_Achelou_ or _Einio_) has the nose-horn
> that curves over onto the premaxillae?
Einiosaurus has the procurved nasal horn, though some individuals
have a smaller erect horn. This may represent sexual dimorphism.
Achelousaurus has the big bosses over the nose and orbits reminiscent of
Pachyrhinosaurus. Sampson describes the horncores of Einiosaurus adults
as being "long, low and rounded", with some of the older individuals
having "pits and masses". I don't know if what he is describing is
similar to the bosses of Pachyrhinosaurus and Achelousaurus.
So: Achelousaurus is tied to Pachyrhinosaurus by the bosses, and
Einiosaurus is tied to Achelousaurus by the fact that both genera only have two
spikes on the frill. Also, the supraorbital horncores in all three genera
are apparently lost otongenetically (the younger animals have them but loose
them as they grow older).