Re: Archosaur Dentition -Reply

["Ralph Chapman" <Chapman.Ralph@NMNH.SI.EDU>]

I can expand this to cover faunal lists is paleontology in general. If a report 
lists a series of taxa from a locality without any supporting illustrations and 
documentation then they should be used with extreme caution. More than one 
paleobiogeographical analysis has had bogus results because of this. In one of 
my other hats, when I work on trilobites, you run into this again and again, 
especially for Cambrian forms where there is so much convergence, especially 
for the cranidium dorsal which can be very similar from group to group. Teeth 
would be subject to the same thing so just think of faunal lists as being 
useful hints of places where things might be of interest.


Ralph Chapman

>>> chris brochu <cbrochu@fmppr.fmnh.org> 11/12/98 09:18am >>>
>chris brochu wrote:
>>
>>  If you don't
>> >believe in tooth identifications you would have to explain why the tooth
>> >characters that can be used to diagnose K coelurosaur groups suddenly no
>> >longer diagnose these groups when you dip below the J-K boundary.
>>
>> I, for one, will not accept archosaur taxon ID's beyond a course taxonomic
>> level, unless the teeth in question are from units where you also find them
>> attached to a skull.  They're about the most plastic part of an archosaur,
>> evolve more rapidly than anything else, can vary within a population more
>> than just about any part, and can mislead very easily.
>>
> Nice.  You could have also mentioned perhaps that none of us have
>done the homework necessary to see what the rates and parameters of any
>of those points you made actually are either...
>

I say this from my experience working with both theropods and especially
crocodylians.  I could pull the teeth from a single alligator, and coerce
someone into making five separate genus-level taxa; I could also assemble a
large collection of bulbous crushing teeth or flattened, serrated teeth
from as many different taxa, and without the rest of the animal any
competent anatomist would think they're from one very-long-lived species.

It would be interesting to measure comparative rates of evolution for
teeth.  My guess is that they'll evolve at different rates for different
lineages - perhaps slower for sauropods, faster for some theropod groups.


chris

Christopher Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

312-922-9410