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RE: Ceratops (was RE: Glishades ericksoni, ...)



Tim Williams wrote-

> Of course there's nothing stopping someone from including _Ceratops montanus_ 
> in a phylogenetic analysis. But this is not the same as saying that there is 
> a *good* reason for including _Ceratops montanus_ in a phylogenetic analysis.
>
> Your suggestion is just special pleading. _Ceratops_ is the name-bearing 
> genus for the Ceratopsidae, and therefore you are pretending it's a useful 
> OTU for a phylogenetic analysis. But it isn't. The type material of _Ceratops 
> montanus_ could belong to any number of derived, brow-horned ceratopsians - 
> including (as noted by Ryan, 2007) _Albertaceratops_. In fact, decent cranial 
> material that was thought by Trexler and Sweeney (1995) to belong to 
> _Ceratops montanus_ was later assigned to _Albertaceratops_.
>
> Including a deliberately phoney OTU like _Ceratops_ in a phylogenetic 
> analysis alongside valid OTUs (like _Albertaceratops_) defeats the entire 
> purpose of a phylogenetic analysis, which is to establish relationships among 
> taxa.

The phylogenetic analysis would still allow us to establish the relationships 
of Ceratops- it just might indicate a range of relationships are possible.  But 
this is useful information to have if we're trying to determine if Ceratops is 
a member of the Chasmosaurus+Centrosaurus clade.

>> It will just
>> make a polytomy in the range of all the taxa it cannot be
>> distinguished from. And if that polytomy is within the
>> Chasmosaurinae+Centrosaurinae clade, then using Ceratopsidae
>> for that clade is just fine.
>
> Does that mean we should include every other crappy ceratopsian fossil in a 
> phylogenetic analysis, simply because it has a name? All those awful 
> _Dysganus_ species, for example? Of course not. There's no reason why we 
> should be treating _Ceratops_ any differently to other ceratopsian nomina 
> dubia.

If you want to determine at what level said crappy fossil is diagnostic at, 
then yes, including it in a phylogenetic analysis is a good way to do that.  A 
precise placement in a cladogram is not the only useful result a phylogenetic 
analysis can provide.

>> My preference would be to only abandon names if the
>> eponymous taxon isn't necessarily located within that
>> clade.
>
> Yes, I agree. But as pointed out by myself and others, there is no good 
> evidence that _Ceratops_ actually belongs in the Ceratopsidae, because 
> non-chasmosaurine and non-centrosaurine ceratopsids may indeed have 
> _Ceratops_like orbital horns.
>
> However, you are advocating defining Ceratopsidae such that it *must* include 
> _Ceratops_, which from where I'm sitting is putting the cart before the 
> horse. If a genus does not qualify as a valid OTU, it shouldn't be put into a 
> phylogenetic analysis. And if the genus can't be put into a phylogenetic 
> analysis, then we shouldn't be using it to name family-level taxa after.

When people say that non-chasmosaurine+centrosaurine taxa may have 
Ceratops-like brow horns, I recall it basically referring to their large size.  
But other variables like curvature, orientation, etc. may apply as well.
Since as I noted, we can include any taxon in a phylogenetic analysis, I 
suppose your criterion would be a family eponym has to have an exact placement 
when included in an analysis?  But this doesn't work either.  Think of 
Troodontidae (or Saurornithoididae if you think Troodon's type is problematic). 
 Last time I heard, we don't know where Saurornithoides or Troodon go in 
comparison to other derived troodontids like Zanabazar, Borogovia, Tochisaurus, 
etc..  How is that different than not knowing where Ceratops goes relative to 
Albertoceratops, Anchiceratops, Arrhinoceratops, Pentaceratops, Agujaceratops 
and Triceratops?

>> "Dubious" is just too subjective a notion.
>
> Not in the case of _Ceratops montanus_. I mean, come on! Two horn cores and 
> an occipital condyle??!!

Lots of valid taxa are based on single elements- Kemkemia, Ozraptor, 
Becklespinax, Iliosuchus, Kakuru, Rapator, Unquillosaurus, Caenagnathasia, 
Pneumatoraptor, Richardoestesia, Itemirus, Urbacodon, the famous Xenoposeidon...

>> Of course this requires actual hard work and
>> exhaustive comparison instead of just saying "Taxon X is
>> only based on one bone whose original diagnosis is no longer
>> valid- it's undiagnostic." Has anyone actually tried
>> to compare Ceratops to other related taxa?
>
> Yep. The hard work has been done, by the likes of Penkalski and Dodson (1999) 
> and Ryan (2007). Based on comparisons with other ceratopsian taxa, both 
> studies concluded that _Ceratops_ was a nomen dubium. (There might be other 
> studies too - these are just the ones that come to mind.)

Penkalski and Dodson (1999) actually wrote that Ceratops' horn cores were 
unusual in projecting almost completely outward, unlike their Avaceratops 
specimen.  Ryan (2007) wrote of Albertaceratops "A reconstruction of these 
horncores, and those of the referred material, suggests that the lateral 
orientation of the horncores appears to exceed that noted for any other 
ceratopsid with large postorbital horncores."  Although he later states 
"individuals of some [chasmosaurine] taxa can show a pronounced
lateral inflection of the horns", the degree of outward projection is not 
specified and would seem to be less than Albertaceratops based on his earlier 
comment.  As Ceratops has almost completely laterally projecting horn cores, 
this might indicate it is synonymous with Albertaceratops.  Remember we'd need 
more than one valid taxon Ceratops is indistinguishable from in order to make 
it a nomen dubium though.  Thus we'd need another ceratopsian with horn cores 
directed as laterally as in Albertaceratops and Ceratops.  Does one exist?  Or 
is horn core orientation variable enough between individuals and throughout 
ontogeny that this isn't actually a useful feature after all?  As far as I 
know, no one's studied the problem, but I don't follow ceratopsid literature 
closely.
 
Mickey Mortimer                                           
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