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McDonald on Rubeosaurus [was Re: Last Dinosaur of 2011]



Andrew McDonald (first author on the paper naming Rubeosaurus) asked
me to forward the following:

*********************
First, a general thought. Neither splitting nor lumping is a valid
taxonomic philosophy. Taxonomic decisions should be made on a
case-by-case basis using the evidence at hand. Yes, I split
*Rubeosaurus ovatus* from *Styracosaurus* and *Uteodon aphanoecetes*
from *Camptosaurus*, but I've also sunk *Dollodon* and probably
*Proplanicoxa* into *Mantellisaurus*, and I agree with Norman (2011)
that *Sellacoxa* is a junior synonym of *Barilium*. Creation of a new
genus for an existing species or the sinking of a genus into another
is no reason to be driven up the wall.

Second, the specifics. Jaime is quite right that centrosaurine
phylogeny is not very robust at the moment. Referral of USNM 14765 to
*Rubeosaurus* added a great deal to the cranial codings of that taxon
(McDonald 2011), but I would not be shocked if the next paper
describing a new centrosaurine reshuffles things, or, for that matter,
if it doesn't reshuffle things. Who knows? My reason for separating
and continuing to separate *ovatus* from *Styracosaurus albertensis*
is simply that none of the recent phylogenetic analyses (McDonald and
Horner 2010; McDonald 2011; Farke et al. 2011; Fiorillo and Tykoski in
press) recovered a sister taxon relationship between *ovatus* and
*albertensis*; instead, *Rubeosaurus* is a member of the
'pachyrhinosaur clade'. In my estimation, keeping *ovatus* in
*Styracosaurus* implies preference for a phylogenetic hypothesis for
which there is no support. With its own genus, *ovatus* can appear in
any position in future analyses without necessitating further
taxonomic revision. *Rubeosaurus ovatus* lacks P1 processes, whereas
all *Styracosaurus albertensis* parietals that preserve that region
exhibit P1 processes of varying prominence. Furthermore, not a single
*Styracosaurus albertensis* parietal, i.e., none of the isolated
skulls or bonebed specimens, bears a medially-inclined P3 spike as in
the holotype of *Rubeosaurus ovatus*. Do you think that some arbitrary
measure of difference should overrule phylogeny? What are "generic
level" versus "specific level" differences? If you disagree with the
splitting of *Rubeosaurus ovatus*, then I think you must present
evidence that supports a sister taxon relationship between *ovatus*
and *albertensis*.

Finally, I want to thank Andy Farke for posting this on my behalf;
this does not represent an endorsement or refutation of any kind on
Andy's part. Also, it's never wise to become too complacent in one's
conclusions, so I thank Jaime and Michael for the interesting
challenge.
Best regards,
Andrew McDonald