Chontriemfanisi apomnemoneumus

On the Consequences of Synonymising Stratigraphically Incompatible Taxa

Coccolithus apomnemoneumus was originally described by Hay & Mohler (1967) from Palaeocene sediments. Varol (2025a) subsequently recorded this species exclusively from Palaeocene material, constraining its range to Zones NP4–NP9 (62.13–56.2 Ma), and reassigned it to the genus Chontriemfanisi as Chontriemfanisi apomnemoneumus.

Nannotax, however, places this form in synonymy with Reticulofenestra bisecta (= Dictyococcites bisectus) — a species whose established range spans the Middle Eocene to the Early Miocene. The stratigraphical incompatibility here is not subtle. Chontriemfanisi apomnemoneumus is a Palaeocene taxon; Reticulofenestra bisecta does not appear until the Middle Eocene, representing a temporal gap of several million years between the two forms. Furthermore, Chontriemfanisi apomnemoneumus and Reticulofenestra bisecta are morphologically and crystallographically distinct — making this synonymy indefensible on every level: stratigraphical, morphological, and crystallographic.

The Nomenclatural Consequence

This synonymy cannot stand without one of two corrective actions. Nannotax must either:

Extend the range of Reticulofenestra bisecta down to the Danian, in order to accommodate the Palaeocene occurrences attributed to Chontriemfanisi apomnemoneumus within its synonymy; or

Remove Chontriemfanisi apomnemoneumus from the synonymy of Reticulofenestra bisecta entirely, recognising it as a taxonomically and stratigraphically distinct entity.

Leaving the synonymy as currently stated is not a defensible position — it is internally inconsistent and stratigraphically incoherent.

The Underlying Problem: Taxonomy Without the Microscope

This confusion is, at its root, a methodological failure. Assigning synonymies — or indeed any taxonomic judgement — on the basis of photographs alone, without direct microscopic examination of the material, introduces precisely this kind of error. Morphological similarity in a photograph is not equivalent. Lighting conditions, orientation, preservation state, and photographic resolution can all obscure or exaggerate features that would be immediately apparent under the microscope.

Rigorous taxonomy demands direct observation. When that standard is not met, errors of this kind — synonymising taxa separated by millions of years of stratigraphy — become not just possible, but inevitable.