Cyclotella alvarniensis: Fossil No More?

by Guillermo Quevedo-Ortiz |

Cyclotella alvarniensis (Figure 1) is considered a fossil diatom species from the Upper Miocene. It displays a distinctive triangular shape and belongs to the centric group. Wüthrich (1979) originally described this species as Fragilaria leptostauron var. alvarniensis, based on several fossil specimens found at the Tourbière du Cachot (Switzerland). In parallel, other studies confirmed the presence of frustules in diatomite samples from deposits in Albacete and Murcia (Spain) (Estrada, 1972; Servant-Vildary, 1986; Foucault, 1987; Straub & Aboal, 1992). There are very few subsequent records of Cyclotella alvarniensis, which raises important questions about its dispersal and geographic distribution (Bertrand et al., 2022). However, it is worth noting that in 2004, a few frustules were found in a subfossil microflora study in Senegal. As the authors pointed out, even assuming a detrital origin for the species, its dating would require more detailed investigation.

Figure 1. Several real images of Cyclotella alvarniensis

During a study on the monitoring and dispersal of diatoms conducted in the Sant Llorenç del Munt i l’Obac Natural Park (Barcelona, Spain), we recorded the presence of C. alvarniensis for the first time in Catalonia. Specifically, it appeared in four different types of modern substrates: flowing-water biofilms, artificial pools, disconnected natural pools, and rehydrated sediment. Given the modes of occurrence and the absence of nearby diatomite deposits, we decided to draft a short scientific note in which we proposed that this may not be an exclusively fossil species. In that note, we encouraged the scientific community to report and re-examine their samples when encountering it. Since its publication in 2023, several researchers have contacted us to share their findings. As a result, C. alvarniensis now appears to exhibit a very particular distribution pattern that warrants further in-depth study.

References

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• Quevedo-Ortiz, G., Bonada, N., & Gomà, J. (2023). Cyclotella alvarniensis (Stephanodiscaceae): Modern or fossil diatom? Anales del Jardín Botánico de Madrid, 80(2), e141. https://doi.org/10.3989/ajbm.586
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