[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Ceratops analyzed in the Sampson et al. (2010) matrix
Tim Williams wrote-
> (1) This same analysis also found _Triceratops_ to be distinct from
> _Torosaurus_ (and _Nedoceratops_). I don't need to elaborate on this one. ;-)
Well, it found Torosaurus and Triceratops (and Nedoceratops) to be sister taxa.
They were entered as separate OTUs, so their distinction was assumed by the
authors. But being sister taxa in the cladogram is just as congruent with the
hypothesis they're synonymous. At worst, this could make Utahceratops a junior
synonym of Ceratops.
> (2) What happens if you include the holotype for _Eoceratops canadensis_ in
> the analysis? (This is NMC 1254, which includes a partial skull, and is
> apparently a juvenile)? The relatively long brow-horns are considered to be a
> sign of the specimen's immaturity. Does _Eoceratops_ pop up in the tree as a
> separate taxon?
Actually, Eoceratops' brow horns are shorter than what are probably adults of
the same species (Longrich, 2010), which matches the ontogeny of Triceratops
and such. I don't know where Eoceratops emerges on the tree though, since I
lack its description. Anyone care to send?
Lambe, 1915. On Eoceratops canadensis, gen. nov., with remarks on other genera
of Cretaceous horned dinosaurs. Canada Geological Survey, Museum Bulletin. 12,
While I'm on the topic of Eoceratops, I just glanced at Mojoceratops'
description and think Longrich's philosophy there is another example of what's
wrong with taxonomy nowdays. Longrich agrees with previous authors that
Eoceratops and Chasmosaurus kaiseni are synonymous, but names a new genus and
species for it based on new specimens! And not because kaiseni is
undiagnostic. As Longrich states-
"Although AMNH 5401 is not referable to Chasmosaurus, the specimen does not
exhibit any autapomorphies, with the possible exception of the transversely
expanded postfrontal fontanelle and the elongate parietal fenestrae. This seems
to be a tenuous basis on which to erect a new taxon. It is conceivable
that the particular combination of primitive and derived characters seen in the
skull could serve to diagnose the taxon. Ironically, however, the otherwise
well-preserved skull lacks much of the single element that is most useful in
recognizing ceratopsians to species level–the parietal. Although in some cases
it is possible to differentiate ceratopsids on the basis of other skull bones
(e.g., Forster, 1996b), in general a parietal is
necessary to make a species–level diagnosis."
Yet in the very same introduction, Longrich says "Like Eoceratops, this animal
[kaiseni] has long brow horns and a sharply hooked squamosal; it also has a
prominent epijugal, a feature unknown in Chasmosaurus. Other unusual features
include a transversely expanded postfrontal fontanelle, and parietal fenestrae
that extend anteriorly almost to the supratemporal fossae."
And looking in the diagnosis of Mojoceratops perifania, what does one see?
"(11) prominent supraorbital horns, length exceeding 200% of basal diameter"
and "(13) epijugal ossification prominent and subconical" in addition to "(9)
parietal fenestrae anteriorly extended towards the supratemporal fossae to a
degree not seen in Chasmosaurus, (10) triangular postfrontal fontantelle with
strong transverse expansion." So kaiseni possesses the autapomorphies, it just
doesn't preserve a parietal. That's no reason to name a new taxon. A holotype
doesn't have to be the most diagnostic specimen. We should be trying to
preserve named taxa, not find any excuse to name a new one. At the very least,
Longrich could have petitioned the ICZN to make what became the Mojoceratops
type the neotype of kaiseni.
As for Eoceratops, Longrich notes the long brow horns and hooked squamosal
distinguish it from Chasmosaurus, but he doesn't say anything about comparison
to Agujaceratops or other long-horned ceratopsines. Just because a specimen is
juvenile is not a reason to ignore it as a holotype.
Mojoceratops perifania should be called Mojoceratops kaiseni at least, and just
maybe should be a junior synonym of Eoceratops canadensis.