Fossil Time Travelers? Scientists Challenge Claim That Oligocene Foraminifera Survived 10 Million Years

In the sun-baked hills of the Sierra de Marmolance near Granada, in southeastern Spain, a seemingly technical dispute over microscopic fossils has erupted into one of the more intriguing debates in modern paleontology. At stake is nothing less than the reliability of the geological clock itself: can certain single-celled marine organisms really persist for ten to fifteen million years longer than scientists have long believed, or were their shells simply swept from older rocks into younger sediments by the restless machinery of an ancient ocean? A new comment published in the Journal of Micropalaeontology by Cesare Papazzoni of the University of Modena and Reggio Emilia and four colleagues makes a forceful case for the latter, challenging a 2025 study that proposed dramatic extensions to the known time ranges of several iconic fossil groups.

The original study, led by Marta Bolivar-Feriche and colleagues, examined sedimentary successions in the Subbetic Domain of the Betic Cordillera, the mountain belt that arcs across southern Spain. Using planktonic foraminifera, free-floating relatives of the bottom-dwelling forms at the center of the dispute, the team dated the succession to the late Burdigalian through early Serravallian stages of the Early and Middle Miocene, roughly between seventeen and twelve million years ago. But mixed into those Miocene-age limestones were larger benthic foraminifera, or LBF, whose characteristic species are otherwise thought to have vanished from the Mediterranean millions of years earlier, during the Oligocene. Rather than interpreting this mismatch as contamination, the original authors proposed that several well-established Paleogene species had quietly survived into the Langhian and Serravallian, forcing a major revision of the standard biostratigraphic scheme.

Larger benthic foraminifera are not obscure curiosities. These shelled protists, some reaching the size of a small coin, dominated shallow tropical carbonate platforms for much of the Cenozoic era, and their rapid evolution makes them indispensable tools for dating marine limestones. The framework most researchers use, the Shallow Benthic Zonation scheme first codified by Cahuzac and Poignant in 1997 and expanded by Serra-Kiel and colleagues a year later, divides shallow-water Cenozoic deposits into numbered zones defined by the first and last appearances of key taxa. The last occurrence of Nephrolepidina and the miogypsinids, for instance, defines the base of zone SBZ 26, while the extinction of the reticulate Nummulites fichteli marks the top of SBZ 22B in the early Chattian. Extending Nummulites fichteli into the Langhian, as the Spanish study implied, would stretch that species’ range by more than ten million years, a move with no support from any other section measured across the former Tethyan realm.

Papazzoni and his coauthors, Andrea Benedetti, Antonino Briguglio, Lorenzo Consorti, and György Less, do not dispute the planktonic foraminiferal identifications, which they accept as convincing evidence for the age of the marly sediments. Their objection centers on a more subtle question: whether the benthic fossils found alongside them actually lived there. The commenters point out that the Sierra de Marmolance limestones were deposited on a prograding ramp within what is now an active thrust belt, a tectonically restless setting where uplift and erosion during the Neogene would have constantly stripped older carbonate rocks and flushed their contents downslope. Robust, hydrodynamically durable shells such as those of Nummulites and the lepidocyclinids are especially prone to this fate. Laboratory and field studies of nummulite banks have shown that these thick, lens-shaped tests resist abrasion and can be eroded from lithified older platforms, transported by currents, and redeposited into much younger sediments as perfectly preserved-looking clasts, a process documented in comparable settings from Baja California to the Apennines.

The geographic details of the original study raise further doubts. According to the comment, the samples containing planktonic foraminifera were not collected within the fossiliferous limestone successions themselves but came from localities roughly a kilometer away from the nearest measured section, with Quaternary debris and soil cover obscuring the lateral continuity of the strata. The original authors described bedding surfaces traceable for hundreds of meters to kilometers, yet they simultaneously acknowledged that covering materials made it difficult to follow those surfaces and precluded systematic sampling of the marls. No planktonic foraminifera were reported from the marly intercalations within the limestone columns, and several samples appear to coincide suspiciously with stage boundaries, weakening the reliability of the first and last occurrence data on which the proposed range extensions rest.

Biometry adds another layer of complexity. Identifying lepidocyclinid chronospecies depends on subtle measurements of embryonic chambers in well-oriented equatorial sections, and meaningful biostratigraphy requires statistically significant populations rather than single specimens, because primitive and advanced morphotypes can coexist within one assemblage. The commenters note that the original study relied on very few oriented sections to identify Nephrolepidina tournoueri and Eulepidina formosoides, and that one figured specimen was too poorly oriented for measurement. Even so, Papazzoni and colleagues concede that the taxonomic identifications themselves appear broadly acceptable, which makes the discrepancy between the fossils and their supposed age all the more striking, and all the more suggestive of reworking.

The paleobiogeographic argument may be the most decisive. In the Mediterranean, Miocene shallow-water assemblages are typically low in diversity and dominated by calcarinids, miliolids, and alveolinids, not by the Oligocene-restricted species reported from Spain. The claimed survival of Nummulites fichteli, Nummulites vascus, and Eulepidina dilatata into the Langhian and Serravallian would require these lineages to persist in isolation while every other Tethyan record shows extinction. The commenters also dismantle a frequently cited Serravallian occurrence of Nephrolepidina aquitaniae from an unknown Spanish locality, noting that the species was originally described from Aquitanian material whose biometric values match Nephrolepidina morgani, and that its supposed Serravallian presence would demand an evolutionary reversal in embryo development. Similarly, the Burdigalian record of Eulepidina in the eastern Tethys reflects a well-documented migration from the Indo-Pacific before the closure of the Tethyan Seaway, not a Mediterranean survival, and the genus Spiroclypeus is essentially a Priabonian to Chattian form whose youngest reliable Tethyan record comes from the Burdigalian of Morocco.

Crucially, the commenters highlight a distinction that non-specialists often miss: sedimentological autochthony does not imply biological autochthony. A limestone bed can form in place, without obvious signs of transport, and still contain fossils that were recycled from older rocks, because in a prograding ramp fed by erosion, the incorporation of well-preserved bioclasts from lithified platforms into younger sediment is a routine process. The original authors dismissed reworking by pointing to the autochthonous character of the facies, but Papazzoni’s team argues that the high-diversity intervals in the Spanish sections more likely reflect pulses of increasing reworking than the survival of ancient lineages. Tellingly, the original authors themselves interpreted the orthophragmines at the base of one section as reworked, an admission the commenters regard as entirely reasonable and one that undercuts the case for treating the other assemblages as in-place communities.

The original study had also suggested that its Langhian Nummulites partly filled the stratigraphic gap between the last Oligocene fossils and modern representatives in the Indo-Pacific, often assigned today to the genus Palaeonummulites. The commenters counter that any such record would postdate the closure of the Tethyan Seaway, meaning an isolated Mediterranean population could not have phylogenetic continuity with Indo-Pacific species, and that a clear lineage connecting fossil Nummulites to the modern venosus form is lacking. Neogene paleogeography instead supports faunal divergence between the Mediterranean and Indo-Pacific bioprovinces, with only a few genera such as Heterostegina and Nephrolepidina persisting into the Upper Miocene of the Indo-Pacific domain. Typical Cenozoic larger benthic foraminiferal species last two to three million years, making a ten to fifteen million year survival extraordinarily implausible.

The commenters close with constructive proposals rather than mere criticism. They recommend searching for calcareous nannofossils in the marly intercalations within the limestones, which would directly date the fossil-bearing beds and reveal whether reworked Oligocene nannoplankton co-occur with the Miocene assemblage, and they suggest strontium isotope stratigraphy to obtain absolute ages for individual specimens versus the bulk carbonate matrix, a technique capable of exposing age mixing within a single sample. For now, they conclude, reworking remains the most parsimonious explanation for the Sierra de Marmolance fossils, and the proposed chronostratigraphic revisions demand far stronger evidence before the textbooks, and the Shallow Benthic Zonation scheme that underpins decades of Mediterranean stratigraphy, should be rewritten.

Subject of Research: Debate over reworking versus range extension of Oligocene larger benthic foraminifera in Miocene deposits of southern Spain

Article Title: Comment on “Chronostratigraphic ranges of Early–Middle Miocene larger benthic foraminifera calibrated by planktonic foraminiferal assemblages (Sierra de Marmolance, Granada, SE Spain)” by Bolivar-Feriche et al. (2025)

Article References: Papazzoni, C. A., Benedetti, A., Briguglio, A., Consorti, L., & Less, G. (2026). Comment on “Chronostratigraphic ranges of Early–Middle Miocene larger benthic foraminifera calibrated by planktonic foraminiferal assemblages (Sierra de Marmolance, Granada, SE Spain)” by Bolivar-Feriche et al. (2025). Journal of Micropalaeontology, 45(1), 309-313. https://doi.org/10.5194/jm-45-309-2026

Image Credits: AI Generated

DOI: 10.5194/jm-45-309-2026

Keywords: larger benthic foraminifera, biostratigraphy, Miocene, Oligocene, reworking, Sierra de Marmolance, Shallow Benthic Zones, planktonic foraminifera, Betic Cordillera, Tethys, paleobiogeography, Journal of Micropalaeontology