RE: Ceratopsian Systematics [was: Avaceratops and Ceratops

[Sherry Michael <_smichael@excite.com>]

Just a side note to add in some more fun, you may also want to consider the
effects of heterochrony(sp?) on ceratopsian evolution. We have to question
if we understand the developmental cycle of these "subadult" animals before
we start bopping them about in systematic classification. I'm thinking of: 

Ontogeny and Evolution of Short-Frilled Ceratopsid Dinosaurs  
Tumarkin, A. R., and Peter Dodson. 1998. A heterochronic analysis of
enigmatic ceratopsids. Journal of Vertebrate Paleontology, 18(3):83A.

In brief, Tumarkin thinks that _Avaceratops_ could have came
from modification that would display seemingly more "adult" traits sooner in
development, while others like _Monoclonius_ would keep juvenile traits in
adulthood.

-Sherry Michael



>>    Having seen _Avaceratops_ many, many times over the last 15+ years
(and 
>>knowing Peter Dodson) - I do know that the classification of _Avaceratops_

>>as a juvenile should more probably be refined as a sub-adult.  Based on
the 
>>occipital condyle being nearly completed fused, this indicates that the 
>>animal was nearly fully mature, and as such its features are more likely
to 
>>be very close to those of the adult form.  Its size is probably 80% of 
>>full-grown. 

>That's backed up the second _Avaceratops_ skull (MOR 694 I think, but I'm 
>going from memory - always a dangerous thing), which indicates a
fully-grown 
>individual of around 5m long.  (I'm going to trust Dodson's referral of
this 
>skull to _Ava_).  The holotype of _Avaceratops_, a subadult individual, 
>probably had a body length of approx 4.2m. 

>Tim 






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