Re: Polacanths and sauropods

[Dinogeorge@aol.com]

In a message dated 2/6/99 3:00:35 AM EST, qilongia@yahoo.com writes:

<< Since the group would have only one genus, it would be redundant:
 the familial, generic, and specific diagnoses would all be identical.
 Why a family, when a genus would do? Monotypic families or other
 suprageneric taxa, I think, are going out of fashion. Hence
 <Ingeniidae>, <Ingeniinae>, <Alxasauridae>, <Blikanasauridae>,
 <Massospondylidae>, <Yunnanosauridae>, and some others are all so
 redundant, they have no taxonomic value. >>

The way to work out monotypic subfamilies and families is to define them as
stem taxa containing all genera (almost always node-based taxa) closer to the
included genus than to its sister genus, subfamily, or family (as
appropriate). This makes a monotypic family or subfamily >not< congruent to
the included genus and gives the taxon a wider scope than its single included
genus. So monotypic familes are not necessarily redundant taxa. Monotypic
subfamiles of monotypic familes are, of course, redundant, even in traditional
Linnaean taxonomy.