[Taxacom] Diagnoses of higher monotypic taxa

Ohl, Michael Michael.Ohl at mfn-berlin.de
Fri Feb 25 03:56:16 CST 2011

I have a general problem to discuss, which I realized when reading (or reviewing) papers which include descriptions of new supraspecific taxa based on a single new species.

In some cases, describers of new species have good reasons to assume that the species discovered should be placed in a genus of its own, perhaps even in a family or order of its own. Such cases of a single species nested in a hierarchy of different higher (redundant) taxa is often applied to fossil insects, mayn which are assumed to be in a quite isolated position. However, this problem exists in all kinds of organisms.

So since alle these taxa are actually redundant, that is, based on a single biological unit, the problem comes up how to diagnose and describe the different (nested) taxa. As far as I see, there are three major solutions to this problem in the literature:
(1)	The ‚bottom-up approach‘
The species is described and diagnosed in detail, whereas the higher taxa are introduced only formally to reflect the position in the classification. Characters potentially diagnostic for the genus or family are not given.
(2)	The ‚top-down approach‘
The highest newly described taxon is described in detail, whereas the included, lower ranked taxa simply refer to this description. E.g., ‚diagnosis of the genus xy: as in the family‘
(3)	The ‚intermediate approach‘
The highest category is described in detailed, and a whole set of (‚empty‘) higher level name is erected based on this species. One of these names on one of several taxonomic levels is then (arbitrarily?) selected and is separately diagnosed by assigning diagnostic characters to it. An example: Symbion pandora has been described as a new species within a newly introduced phylum (Cycliophora), class, and order, all of them monotypic and, thus, redundantly based on this species. The intermediate categories are diagnosed simply be the statement ‚same as the phylum‘. However, for reasons unknown to the reader, the  new order (and not another category) is diagnosed as ‚same as the phylum, with metagensis in the life cycle‘.

>From my point of view, the logic here is that the only empirically justifyable taxon is the species, which can be diagnosed based on a set of characters. All other higher taxa are formal additions just to adopt its classificational position to the existing classification. Thus, from a biological point of view, only the bottom-up approach makes sense at all. However, based on a brief paper search, I have the impression that the top-down approach is applied more frequently.

One note: This discussion obviously only makes sense within the Linnean hierarchy, which can be questioned totally. However, I would like to raise this questions within the framework of the existing Linnean hierachy.
So I am very interested to learn more about the opinion on that from list members!

Michael Ohl
Museum fuer Naturkunde, Berlin

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