splitting headache

["Considine, Blaise" <bpc.apa@email.apa.org>]

No, this isn't a flame. With the recent talk of splitting, especially 
regarding stegosaurus in the Morrison formation, I was wondering, just 
when would a species become a species? That is, what differentiates two 
species from each other rather than them being cases of a) individual 
differences within a species occurring at the same time, or b) changes 
within a species that have occurred over a period of time. If I've gotten 
anything from the cladistics discussions, would the difference lie in the 
occurrence of a particular characteristic? That is (and I do this more 
because I'm not quite sure if what I'm saying is what I mean) species A 
has a particular characteristic that species B does not have (or would it 
be vice versa)? I'm not necessarily trying to start an evolutionary 
theory discussion here, though if a gradualist approach to dinosaur 
evolution doesn't hold and a punctuated approach does, please feel free 
to provide examples.
Blaise "Another satisfied Dino-list customer" Considine 
[bpc.apa@email.apa.org]