[Taxacom] Diagnoses for monotypic genera

Mario Schädel mario.schaedel at gmail.com
Sun Jul 11 11:56:01 CDT 2021

Dear Taxacom readers,

from time to time, reviewers and editors complain about how my 
colleagues and I handle diagnoses for species which can not be 
identified as belonging to an existing group that is ranked as ‘genus’. 
Based on the underlying logic in my opinion it is best to give a 
diagnosis for the species and then for the monotypic genus either write 
‘as species’ or ‘not applicable because monotypic’ (I would prefer the 
latter solution).

Are there publications arguing for this procedure? It would be very 
convenient to point reviewers or editors to such a publication instead 
of writing long-winding explanations why we think the two alternatives 
(below) are a bad idea. To explain myself in a bit more detail: The 
alternatives to my preferred ways are:

1. splitting up the diagnosis into a genus and a species part (this gets 
suggested the most).

The decision whether a character is genus or species level is obviously 
very subjective and arbitrary. Whether such a decision was correct can 
only be known when and if a second species gets discovered. While it is 
arbitrary and subjective, this may sound trivial; however in practice I 
find it to be problematic.

2. giving a diagnosis for the genus (exactly as I would formulate it for 
the species) and then for the species writing ‘as for the genus’.

This may sound even more trivial. ‘as for the species’ – ‘as for the 
genus’ – Where is the difference? The difference is that in practice 
many authors do not critically check what assumptions there are behind 
diagnoses. Even more so if they come from well established colleagues. 
Subsequently, authors simply include a new species into an existing 
genus if the new species matches the description of the genus, instead 
of thinking about synapomorphies between the two species.

In my opinion, not providing diagnoses for the genus can be very helpful 
in this regard, as it doesn’t lure future authors to a convenient but 
potentially wrong solution. In my field – I work with arthropod fossils 
– there are numerous examples of genus names that turned into garbage 
taxa because of exactly this process. Extinct species are especially 
prone for this and with those the process of untangling such messes is 
even harder, because there is only incomplete morphological data 
available. Yet, I can imagine such things to also be problematic in 
fields where there are only few resources available for reconstructing 
phylogenies using molecular or combined data.

I would be very happy if someone could point me towards publications 
that deal with this problem, which I then can reference to, when needed.

Best wishes,

Mario Schädel

PhD Student
Ludwig-Maximilians-Universität München
Munich, Germany

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