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Morphological Identifications



An interesting article brought to light by those wonderful folks at
Discovery Channel
        Two scientists,( names?:( ) completed comprehensive DNA testing on
the renowned chambered nautilus. According to morphological identification
and
speciation-(meaning the number of distinctly identified species) there
were 9 different species believed to exist, with one exception, the King
Nautilus. (Believed to be the most primordial and ancient- a true "living
fossil".) Before the study, it was considered to be either the
original or pretty near the orginal ancestor of the others. The testing
proved conclusively that only TWO species existed!, AND, interestingly
enough, the King turned out to be the more recently developed of the two!
I found this turn of events to be both fascinating and frustrating and
wanted to mention it for several reasons...

1) I found it intriguing and thought others might also. The show is well 
worth checking out.  :)
 
2) Reading the underlying message from Steve got my gears grinding. I
would bet my last dollar (being an undergrad, I am sure it is somewhere
right around here) on the chance of the results being, in no way, an
isolated incident.
        It's part of the frustrating same old, same old. Unless we get a
"window through time", it seems that some assemblages, linneages,trees/bushes
etc. will be nearly impossible to complete with certainty -> and thus,
accuracy. Perhaps with this little nautilus scenario, Eoraptor/
Plateosaurus could be viewed as one or the others ancestor. I am
speaking from a knowledge base ( my own) that's not quite extensive in
specific species of dinos, but the point is still clear, I think. Even
with a cladistic program printing out a tree ( wish I could properly use
the systematics buzzwords here- parsimony, homogeny, etc.) it seems that
much information could be just plain old inaccurate in some studies and
classification systems. Of course, that is no reason to stop research and
information gathering, but I think the results represent some of the
pitfalls of modern research, and in cases like species identification from
fossilized remains, it appears that the pit can be pretty deep. sigh
Responses welcome! 

 On
Thu, 23 Jul 1998, Tomporowski, Steve wrote:

> 
> Well, the bottom line is:  Do we have *any* data that indicates what species 
> concept is correct??  Having concepts of what is happening is fine, but the 
> real advances come when the concept gives of model of reality.  I infer from 
> what you've written that we probably don't have enough data *and* there is a 
> distinct possibility that one concept is not valid all the time.
> 
> Didymus
> >
> >   Why does the fact that _Eoraptor_ appears later or contemporaneously
> >with _Plateosaurus_ in-and-of-itself disqualify it from being
> >_Plateosaurus_'s ancestor?
> 
> It depends on the species concept being used.  The phylogenetic species
> concept would argue that the ancestral species goes extinct upon
> speciation, even if one of the daughter lineages is indistinguishable from
> the ancestral lineage.  (I'm limiting myself to cladogenetic speciation
> here - anagenesis is another issue altogether.)  As such, ancestors must
> predate descendents in a perfect fossil record. But, if your species
> concept accepts post-cladogenetic survival of the ancestor, and you are
> willing to accept durations for species in the tens of millions of years,
> then stratigraphy by itself is not a disqualifier.
> 
> 
> 
> chris
> 
>  -=--=--=--=--=--=--=--=--=--=
> Christopher Brochu
> 
> Postdoctoral Research Scientist
> Department of Geology
> Field Museum of Natural History
> Lake Shore Drive at Roosevelt Road
> Chicago, IL  60605  USA
> 
> phone:  312-922-9410, ext. 469
> fax:  312-922-9566
> 
> cbrochu@fmppr.fmnh.org
> 
>