I started a flag on flavescens to not clog up the Carnivora flag, but for completeness, it's here: https://www.inaturalist.org/flags/318256

@henrydelange @tonyrebelo @johnnybirder @jakob @bobby23 @loarie
Any thoughts on splitting nigrata from flavescens?

This is the MDD citation for nigrata: Rapson, Sara A., Anne W. Goldizen, and Jennifer M. Seddon. "Species boundaries and possible hybridization between the black mongoose (Galerella nigrata) and the slender mongoose (Galerella sanguinea)." Molecular phylogenetics and evolution 65.3 (2012): 831-839.

But this paper doesn't address AT ALL the fact that many taxonomists think G. nigrata is synonymous with G. flavescens. Everyone agrees it's distinct from sanguinea, but the question is whether black forms should be nigrata and red forms should be flavescens, or whether both those forms are conspecific. Kingdon's Mammals of Africa follows MSW3 in keeping them conspecific, citing a number of sources, but also saying there isn't really enough information yet.

There's more discussion in Rathbun, Galen B., and Tristan E. Cowley. "Behavioural ecology of the black mongoose (Galerella nigrata) in Namibia." Mammalian Biology-Zeitschrift für Säugetierkunde 73.6 (2008): 444-450.

I have no feelings one way or the other. It looks uncertain and inconclusive, so any option is still way open.

Personally, I would prefer to err on the side of the most detailed. it is far easier later on to sink two taxa, than to later on split them. Assuming that IDs can be easily done from photographs (or less ideally location), and that ID issues dont become a problem.
I dont think that we should be making these sort of calls on iNat. We should be following a respectable source and letting them make the decisions. Where alternative sources are in conflict we have to decide whom to follow.
I dont think it is a case of minimal evidence. We need to go with the scientific literature. The split was in use in 2008, and no strong rebuttals to sink the species have been published since then. MMD still considers them split. If we are following MMD we should split.
QED.

Will Figure 1 of https://sci-hub.tw/https://doi.org/10.1016/j.ympev.2012.08.005 not be adequate?

@tonyrebelo The question is whether the range for G. nigrata from Rapson 2012 (below in gray) should be cut from the range for G. flavescens (in pink) or not. The IUCN taxonomic concept for flavescens includes regions that are in Rapson's nigrata (because nigrata is considered a junior synonym). Are both species present in those areas? Is only nigrata present? Are they in fact conspecific?

Sorry: I have misread the issue.

In southern Africa we follow Smithers (now Skinner & Chimumba): the Mammals of the southerrn African subregion.
Since 1993 nigrata has been treated as a synonym of flavescens (as have shortridgei and annulata).

Common names are Kaokoland Slender Mongoose and Larger Red Mongoose, but the field description says: "in the field they look black overall".

Why nigrita is now being used is unclear to me, but the Table 1 of Rapson, S. A., Goldizen, A. W., & Seddon, J. M. (2012). makes it clear that there are only 3 species in in the Genus in southern Africa - hence nigrita is thus the same as flavescens and not a fourth species.
But, flavescens dates from 1889, and nigrita from 1928, so perhaps the change is a technicality? (e.g. the type for flavescens might be sanguinea, hence nigrita is representative of the taxon, but this is pure speculative example). There is no mention of flavescens in the paper or the references which is really weird on all accounts - as if they are pretending that the name does not exist. They quote S&K in the table as the source for sanguinea and pulvertina, but dont mention anywhere that S&K have a third species flavescens.

perhaps this poster explains what has happened: https://www.waterberg-wilderness.com/pdf/Poster-UQ-2007.pdf - But why good taxonomy is not being followed is beyond me.

In their introduction to the genus S&K write in 2005:
"In the light of such uncertainty surrounding the taxonomy of Galerella, this edition follows Wozencraft (1993) in provisionally regarding Galerella as separate from Herpestes, and recognises three species of Galerella in the subregion: G. pulverulenta, G. flavescens (which is the senior synonym for nigrata), and G. sanguinea. Although listed as such by Wozencraft (1993), G. swalius is not recognised as a monotypic species pending clarity on its status (Taylor & Goldman, 1993). Furthermore, G. swinnyi based on two skulls (one broken) without skins and regarded as incertae sedis es is not included in the species accounts. In both specimens the zygomatic arch and the postorbital process do not form a posterior bony ring around the eye socket. In cranial size it is intermediate between G. sanguinea and G. pulverulenta (Watson Dippenaar, 1987).

All this is already in iNats taxonomy for the species. Sorry I got sidetracked by the pulverulenta - flavescens issue: and did not realize that this was about nigrita and flavescens.
I see nothing in the literature to suggest that anyone is proposing that these are separate species. The concept if flavescens is already strange, but for 3 species to co-exist - two with almost totally sympatric ranges - is higly improbable.

In the current public form of the MDD, nigrata is not considered a valid taxon and is lumped with Herpestes flavescens with the following note: includes nigrata, which is occasionally recogniced as a distinct species; moved from Galerella to Herpestes (since the type species, H. ichneumon is genetically within or basal to Galerella species based on different molecular analyses)" (sic). Here is the full page.