[Taxacom] Diagnoses for monotypic genera

Scott Thomson scott.thomson321 at gmail.com
Mon Jul 12 11:57:58 CDT 2021

Hi Mario,

I cannot think of any specific papers on this issue either so can just give
an opinion. I consider describing the genus and the species as two separate
issues however I agree with monotypic genera this is complicated by the
reality that all the characters possessed by the species are also likely
diagnostic for the new monotypic genus. For the genus I look at what
characters already exist in the lit for related existing genera and use the
difference here for the genus diagnosis. Assuming there are related genera
of course. But at least here synapomorphy can come into play and how this
new genus has diverged from other already defined genera can be identified.
As Les pointed out this may also require redefinition of existing genera to
clarify the diagnosis.

The species diagnosis although technically including the genus diagnosis
can then focus on those characters that are autapomorphic which though may
not have phylogenetic signal do still give characters capable of
identifying further specimens of the taxon. This may be important for
fossils in particular as they are generally incomplete and down the track
they can be associated to species and further characters may be developed
in the future. I agree that whether or not a character is a genus or
species level character is subjective, my approach is trying to make it
useful for the future addition of specimens for further study.

Cheers Scott

On Sun, Jul 11, 2021 at 1:54 PM Mario Schädel via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> 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
> --
> he/him
> PhD Student
> Zoomorphology
> Ludwig-Maximilians-Universität München
> Munich, Germany
> mcranium.github.io
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Scott Thomson

Centro de Estudos dos Quelônios da Amazônia - CEQUA
Petrópolis, Manaus
State of Amazonas, 69055-010

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