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Re: Princeton Field Guide



----- Original Message ----

From: Jaime Headden <qi_leong@hotmail.com>
>  I missed Scannella's talk (by not having attended) but I've read the 
> abstracts 
>presented on this topic, and I've read the paper on which this talk is based 
>(i.e., the *Triceratops* taxonomy one), so you will pardon me if this was 
>brought up at all and addressed (by this paragraph quoted above, I will say 
>"no."

If you'd have seen john's talk (which I wont discuss) then you'd have seen how 
we treat Triceratops is based on the most complete fossil record of any 
dinosaur. Most individual fossils. Highest precision strat data. Multiple 
growth 
stages. Multiple "species".



>  If you, or anyone, insist that "there is only one taxon" (Scannella and 
>Horner, 2010) of ceratopsid in the Hell Creek beds of the Maastrichtian, then 
>you are making an arbitrary lumping point without ANY sense of diversity 
>measurement at all. It is also entirely inaccurate, as there are TWO "species" 
>by Scannella and Horner's count, not one (that's two), a "genus" (three), a 
>"subfamily" (four), and a "family" (five); if we want to conflate this further 
>up by including other taxa (like *Leptoceratops gracilis*), we can go all the 
>way to *Coronosauria* (which will include *Ceratopsomorpha,* *Ceratopsoidea* 
>[if 
>not explicitly than my extension] for six and seven) and *Ceratopsia,* 
>*Marginocephalia,* *Genasauria*.... So there are quite a few "taxa" (some 
>unnamed but implied according to the ICZN -- if you want to use ranks like 
>"species" and "genus," which Scannella and Horner seem to do). Scannella and 
>Horner, and Horner and Goodwin on *Pachycephalosaurus*, certainly do think 
>there 
>is a real quality that can be used called a "genus," and have insisted that 
>each 
>Hell Creek taxon was limited to "one" genus with as many species as seems to 
>be 
>suitable (see *Triceratops*).
<snip>

None of this has any relevance. At any given point in time, there is only 
evidence for one ceratopsid in the Hell Creek Fm: Triceratops. It evolves over 
time 
all these species if 
you like,. I do not care: they are representative of a single anagenetic 
lineage.

back to jaime:
>>  So when you conflate the idea of "diversity," but offer no means of 
>> measuring 
>>it objectively, then like Paul does, you start making arbitrary lumping 
>>actions 
>>that come under fire -- not because someone thinks you are treading on 
>>"their" 
>>taxon, but because it is SO _individually_ arbitrary; you are literally 
>>making 
>>up your mind taxon to taxon, rather than applying a suite of reasoned 
>>arguments 
>>you will then use objectively to any taxon you find. When the decision is 
>>made 
>>in this manner to "lump" a taxon (and then go make several press statements 
>>supporting this decision) I question the sense that "diversity" is in any way 
>>part of the decision-making process. This is largely due to the fact that 
>>"genus" has nothing to do with diversity, unless specifically defined as 
>>such, 
>>and no one has yet to formally perform a broad systematic "perspective" on 
>>hat 
>>happens if you make a "diversity"-based model for taxa using Linnaean 
>>taxonomy 
>>as your benchmarks for "levels" of diversity.

Taxa are testable by ontogenetic analysis, and by stratigraphic analysis. If 
all 
your "species" turn out to be contemporaneous and of different ontogenetic 
ages, 
then you probably are just naming growth "stages" of a single "species" as 
different "species". that is the point of the Triceratops-Torosaurus work. If 
you have two specimens of similar/identical growth stage, but are 
morphologically distinct, then you can test them stratigraphically. if they are 
stratigraphically equivalent, then they may truly represent multiple "species", 
or individual variation within a single "species". 


Diversity = number of individual lineages present at one point in time. call 
those lineages what you want. divide them up how you want. They are simply 
morphologies changing over time. When true cladogenesis occurs, you get a 
splitting of that lineage. Diversity goes up until one of those linea
st part, you're operating within the old 
cope-marsh paradigm that only considers morphology alone, not morphology as a 
product, and doesn't consider trends in morphological change, just seeing the 
world in black and white. Lumping is not arbitrary. Taxa are testable 
hypotheses. if you don't do ontogeny or stratigraphy (or didn't collect/report 
that data), then yeah: it's just arbitrary opinion, but we actually do study 
these things. We can test taxa.