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Re: Paradoxically temporal

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.

>   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.


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