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Re: More tyrant Q & A's

At 08:55 PM 12/9/98 +0100, Berislav Krzic wrote:
>I second that opinion.
>What about subspecies? Some recent big mammal subspecies vary significantly
>in size (Loxodonta).

Yes, but *by* *definition* subspecies *cannot* be sympatric.  (Though the
boundary between subspecies can change with time, quite quickly even).
Morphic variation within a single population is just that, variation, it
has no taxonomic status.  And sympatric forms that do not interbreed are,
by definition, distinct species, no matter how similar they are.  Thus
forms in different levels may be subspecies, or forms in different
geographic areas may be so, but forms side by side in the same quarry
cannot be.

Overall, as things stand now, the most parsimonious explanation for the
variation in _Tyrannosaurus_ in North America is sexual dimorphism.  The
difference in the prominence of display structures on the head actually
reinforces this, as sympatric closely related species tend to *maximize*
display differences.  That is, the expected case for sympatric species
would be two distinct, but equally prominent, types of display structures.

May the peace of God be with you.         sarima@ix.netcom.com