Re: Horner and Goodwin on Triceratops

[Tim Williams <twilliams_alpha@hotmail.com>]

Jamie Stearns wrote:

> I don't really see a lot of good ways to classify the various 
> ceratop(s?)ids, myself. On one hand you have those who would make up new 
> species for every minor horn/frill variation,

That used to be an issue, especially with the erection of new species of 
_Triceratops_ and _Monoclonius_.  This is not so much of a problem these 
days.

> and on the other, there are those who would dump everything into one 
> species and cite "individual variation" to explain away the differences.

I would say that ontogeny rather than individual variation per se may 
explain away certain differences.  For example, Sampson et al. (1997) 
presented a strong case that _Brachyceratops_ and _Monoclonius_ represent 
subadult specimens of other centrosaurines_.  More recently, Norell and 
Makovicky (2006) suggested that _Platyceratops_, _Lamaceratops_ and 
_Magnirostris_ may all fall within the range of ontogenetic variation 
observed (or inferred) for _Bagaceratops_.  (BTW, I'm not advocating the 
latter hypothesis; I'm just drawing attention to it as an example of 
differing viewpoints on taxonomy.)

> I seem to recall horridus and prorsus were mainly separated on the basis of 
> the nasal horn being anteriorly curved in prorsus, posteriorly curved in 
> horridus,

I'm not sure this was one of the characters used to separate _T. horridus_ 
and _T. prorsus_, although the curvature of the brow horns and relative 
length of the nasal horns were cited.

Briefly, the characters were:
Length of the nose horn core (longer in _prorsus_);
Length of the rostrum anterior to the nasal horn core (longer in _prorsus_);
Length and angle of the orbital horn cores (shorter and more anteriorly 
inclined in _prorsus_ - 60 vs 90 degrees relative to the horizontal);
Presence of frontal fontanelle (present in _horridus_ but not _prorsus_);
Dorsal border of lower temporal fenestra (jugal in _horridus_, squamosal in 
_prorsus_) .

So Forster used more than just the size and angle of the horn cores to 
separate the two _Triceratops_ species.

> similar to the situation of apertus/nasicornus in Centrosaurus [snip] Could 
> this mean Centrosaurus species ought to be reevaluated as well?

Most _Centrosaurus_/_Monoclonius_ species have already been synonymized with 
_C. apertus_, including _dawsoni_, _flexus_, _nasicornis_ and 
_longirostris_.  The species _C. brinkmani_ was recently erected by Ryan and 
Russell (2005), based on differences in horn core morphology and frill 
ornamentation between it and _apertus_; but these characters appear to fall 
outside the range of variation seen in _apertus_.

David Marjanovic wrote:

> Yes, it should be, but it isn't. The ICZN now forbids the correction of 
> "incorrect latinizations" and the like as "unjustified emendation", so we 
> are stuck with what some call a "barbarism".

(Begin rant)

"Barbarism" is the word.  Recent Chinese fossil bird papers in particular 
are fertile ground for badly named families.  Here, incorrect latinization 
takes a back seat to bad spelling.  Hopefully we won't be stuck with names 
like Aberratiodontuidae (from _Aberratiodontus_), Gansuiornithidae (from 
_Gansus_) and Yandangithidae (for _Yandangornis_) forever.

(Rant complete)

Cheers

Tim