Variants


The problem - splitting and lumping

There is always debate in taxonomy, and especially in palaeontological taxonomy, about how many species to recognise. A common way of describing this is to contrast splitters and lumpers, where "splitters" are keen to recognise as many morphotypes as possible, whilst "lumpers" prefer to use a smaller number of more generalised morphospecies. This division also often reflects the purpose of the study; for biostratigraphy it may be useful to recognise any morphological subdivision, so long as it has a discrete stratigraphic range. By contrast for quantitative palaeoceanographic studies it may be more useful to reduce the set of taxa used to a relative low number, in order to simplify statistical analysis of data, and to maximise data reproducibility. Likewise in very well preserved material it may be practical to recognise far more morphospecies than in poorly preserved material.

The issues raised by these factors have recently been brought to the fore in Cenozoic nannofossil studies by the work of the BP research group as published by Bergen et al. 2017, Blair et al. 2017, Boesiger et al. 2017, Browning et al. 2017 and de Kaenel et al. 2017. They proposed a new taxonomy for the Neogene with about 50% more species than most previous studies and allowing a much higher biostratigraphic resolution through both use of more species and use of abundance decreases and increases in addition to first and last occurrences.

Variants on Nannotax

On Nannotax our objective is both to document the taxonomy and to provide guidance on how to use it. We have always regarded the main catalog as a subjective recommended taxonomy and have always noted as possible variants taxa which we do not recognise but which other workers might do. Another term for these is subjective synonyms. In other places we have noted that some species we do recognise might be regarded as variants by other workers. NB In this context we use the term variant rather than variety, since variety has a formal meaning as a taxonomic rank within the classification system, whereas variant is an informal subjective indication of our opinion.

However, to handle the alternative taxonomies of highly-experience biostratigraphic splitters and more general users we are now treating some species as sub-taxa of other species. Such species will still get separate pages and so consistent documentation and imaging but they are explicitly indicated as being variants, and so taxa which are not recommended for use by novices, or for use in palaeoceanographic studies, or for use in study of poorly preserved material. It is hoped that this approach will allow us both to usefully document the concepts behind the variants, and to clearly indicate that they are not taxa which we recommend for general use. It also has the practical advantage that it is very easy to apply, changing a taxon status between being shown as a separate species and a variant requires minimal editorial work but has strong impact.

This is a work in progress and we have not systematically revised all taxa to apply the variant labelling consistently. The designation of species as variants is subjective and may change, so debate on individual cases is welcomed. Please do use the comments sections at the bottom of every page (all comments also appear on the Recent comments page).

Summary

Taxa flagged as variants may be of value to expert biostratigraphers, but are not recommended for general use.