non-exclusive keys

[ewan fordyce]

Forgive me if I have overlooked this thread perhaps better explained in
earlier correspondence, but another way to look at keys which include
"non-exclusive" or "default" lines is to view the exclusive line as
identifying the synapomorphy or autapomorphy for one group, leaving the
other line for a paraphyletic mass of taxa still to be explored.  An
example for cetaceans (whales) might be -

*Baleen present: Mysticeti    [identifies a synapomorphy for a particular
clade - and in this case only the one character is needed]
*Baleen not present/ not as above    [allows us to eliminate one clade and
move on through the key to other key lines, other synapomorphies or
autapomorphies, and other taxa]

Such a cladistically-oriented key would probably be quite workable to a
cetacean systematist.  This comment is not meant to suggest that keys must
equate directly with  cladograms.

Ewan Fordyce