RE: Maidment & Wei, 2006

[Michael Mortimer <mickey_mortimer111@msn.com>]

leachjeff@hotmail.com wrote-

> hummm, let's see if i can elegantly extract my foot from my mouth. If i 
> understood the article (Maidment & Wei 2006) correctly it argues that Chinese 
> Late Jurassic steogsaur diversity was similar to that found in the rest of 
> the world instead of more diverse as previously assumed. The number of genera 
> is reduced from five to three with _Monkonosaurus_ and _Chialingosaurus_ 
> declared nomina dubia because the material referred to each genus lack 
> autopomorphies. Nothing radical here, just wish they had photographed the 
> material in question, so i could see exactly what they are talking about. 
> Here is the problem. _Monkonosaurus_ consists of an ilio-sacral block with 
> the possibility that some dermal plates and partial vertebrae might show up. 
> Being only three stegosaur genera in Late Jurassic China this ilio-sacral 
> block should be referrable to one of them (The closest resemblence i saw was 
> to _Wuerhosaurus_). No such association is made so in my opinion there is at 
> least four genera. A
 similar line of reasoning can be used with _Chailingosaurus_. The authors 
point out that there are two possible stegosaurs among the _Chailingosaurus_ 
material and CV207 originally referred to _Chungkingosaurus_ doesn't belong to 
that genus. So there is a possibility of up to seven genera among the material. 
I can also add that the material referred to _Huayangosaurus_ might also 
contain material from another stegosaur. The status the authors assigned to 
_Monkonosaurus_ and _Chialingosaurus_ is in my opinion premature. There is 
enough material assigned to each genus that there is every hope that future 
finds could be referred to them. Future research might find more characters 
related to the ilio-sacral block of stegosaurs allowing _Monkonosaurus_ at 
least to be described as a unique combination of these characters (there is at 
least one new character in Maidment, Wei and Norman 2006). So the claim that 
there is only three stegosaur genera in the Late Jurassic Chinese material isn't
 substansiated. There are three valid genera!
, two pro
 more genera (even more if you include nomina nuda). more later

Well, since no one has replied yet, I'll give it a go.  I think your main area 
of misunderstanding is that there is a difference between the number of 
diagnosable species and the number of actual species we have remains of.  There 
are lots of dinosaurian nomina dubia and unnamed specimens which are near 
certainly distinct from named species based on provenence alone if nothing 
else, but since we can't prove this validity, it doesn't mean much for 
diversity studies.  Honestly, I think dinosaur diversity studies are a waste of 
time due to this factor and the rarity of diagnosable dinosaur remains in 
general.  With the Morrison Formation showing us such great diversity (with new 
species still being discovered), the known diversity from most other formations 
is basically a consequence of what happens to have been excavated and described 
at the moment.  I agree the concluding sentences of Maidment and Wei are poorly 
worded, but I think their main point was that the _known_ diversity of
 stegosaurs was not significantly higher in China than in Europe or America, 
contra Dong.  This point is strengthened by their 2008 paper's review of 
European material, where they conclude most of the specimens traditionally 
assigned to Lexovisaurus and Dacentrurus can't be certainly referred to those 
genera.

My own problem with Maidment et al. (2008) is that is seems overly cautious 
when referring specimens to taxonomic groups.  Though outside my area of 
expertise, it surprises me so many specimens previously referred to Stegosauria 
can't be distinguished from sauropods or ankylosaurs.  Just because they don't 
preserve utilized synapomorphies of Stegosauria doesn't mean they can't be 
shown to be more similar to stegosaurs than to any other group.

Mickey Mortimer