Ross Mayhew wrote,
> The grouping of a number of similat genera into a "tribe" often seems to
be a semi-arbitrary process, with frequent disagreements amongst the experts
in a given field.  A better question may be "If you have a group of genera
which you deem sufficiently similar to warrent grouping them together in a
less than family - oriented manner, how do you decide whether to call the
resulting taxa a "tribe" (a term very seldom used in molluscan taxonomy, for
some reason), or a "sub-family"??  Is there any hard and fast difference
between the two taxonomic categories, other than that the "tribe " is deemed
to be a slightly more cohesive or tighter grouping than that of
"sub-family"?

The ICZN allows the use of many taxonomic ranks. When a new family is named,
that automatically also names all of the lower ranks that contain the type
genus. That is, when the family Pectinidae was named, it also created the
subfamily Pectininae (including type genus Pecten), and the tribe Pectinini,
and so on, all attributed to the same author and date. The tribe is lower
than the subfamily.

If a taxonomist feels it is necessary to parse a family into subfamilies and
tribes, then he or she does so. In practice, the tribal rank is commonly
used in entomology but not very often in malacology.

Subjectivity in taxonomy is gradually being reduced by the use of the
cladistic approach, and will be nearly eliminated when gene-sequencing
techniques become more widespread. Taxonomy will then be based directly on
similarities of DNA among species.

Already it is clear that no two families of organisms really have comparable
rank, but merely a subjective approximation to a similar rank. That is still
useful for the purposes of discussion, but it is not clear how much longer
the Linnaean system will last. At present, there is still nothing better to
replace it as a convenient way to classify living organisms.

Cheers,
Andrew

Andrew K. Rindsberg
Geological Survey of Alabama

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