Ancient Giants Under Fire: Spanish Fossils Ignite a Fight Over Miocene Timelines

Deep in the hills of southern Spain, a quiet scientific dispute has erupted over some of the ocean’s most remarkable microscopic architects: larger benthic foraminifera, single-celled organisms the size of small coins that once carpeted warm, sunlit seafloors. In a reply published in the Journal of Micropalaeontology, a team of European researchers has mounted a robust defence of findings that, if correct, force a rethink of how geologists date Mediterranean rocks spanning a critical chapter of Earth’s climatic history. The exchange centres on the Sierra de Marmolance near Granada, where limestones laid down during the Early and Middle Miocene epoch preserve an unexpectedly rich record of these giants of the protist world.

The original study, led by Mónica Bolivar-Feriche of the University of Ferrara together with colleagues from the Universities of Granada and Ferrara, reported something startling. In the Marmolance succession, limestones packed with larger benthic foraminifera are interbedded with marls, fine-grained muddy rocks that contain planktonic foraminifera, free-floating relatives whose evolutionary turnovers provide one of the most reliable clocks in the geological record. By calibrating the benthic assemblages against these planktonic markers, the team documented Nummulites species surviving into the Langhian stage, roughly 15 million years ago, alongside Serravallian-age lepidocyclinids and the enigmatic genus Risananeiza. Those ages are far younger than many specialists expected for such fossils, and the claim immediately drew fire.

A group led by Cesare Papazzoni published a formal comment in the same journal, questioning the interpretation. Their central objection was elegant in its simplicity: the foraminifera in question, they argued, must be reworked. In sedimentology, reworking describes fossils eroded out of older rocks and redeposited in younger sediments, like pebbles carried downstream. If the larger benthic foraminifera of Marmolance were simply washed in from Oligocene deposits tens of millions of years older, the planktonic foraminifera could still date the rocks correctly while the benthic fossils would say nothing new about evolution. The commenters also questioned whether the marl samples used for dating had truly been collected from within the limestone succession, and whether the stratigraphic correlations between different outcrops were secure enough to support the bold conclusions.

In their reply, Bolivar-Feriche and her co-authors, Jesús Reolid, Julio Aguirre, Davide Bassi and Juan C. Braga, concede little. They begin by welcoming two points of agreement: the commenters accept that the planktonic foraminifera are correctly identified, and that the taxonomic assignments of the larger benthic forms are broadly acceptable. That matters, because an earlier criticism had suggested the age-defining planktonic assemblages looked suspiciously Oligocene in character. With the identifications themselves off the table, the debate narrows to a single, sharply defined question: are the benthic fossils in place, or are they intruders from an older world?

The team’s answer rests on quantitative evidence gathered from 147 thin sections, microscope slides cut through the limestone and examined point by point. Using cluster analysis on the proportions of benthic species, planktonic foraminifera and siliciclastic grains, they distinguished distinct larger benthic foraminifera facies, each defined by a characteristic assemblage. The statistical reality of these groupings was tested with one-way analysis of variance, a standard method for confirming that differences between groups exceed what random variation would produce. The result was a set of facies that repeat consistently across all five sampled sections of the Sierra, replacing one another vertically through tens of metres of strata, sometimes with gradual transitions, and never mixing within the same beds.

That spatial and temporal segregation, the authors argue, is the smoking gun. On a carbonate ramp, the gently sloping platform that fringes a coastline, different water depths host different communities, and each facies belt leaves its own fossil signature. If waves or currents had swept older fossils onto the ramp, particles with similar hydrodynamic behaviour, which these shells share, would be scattered indiscriminately across the deposits. No sedimentary process, the reply contends, can sort reworked material into such cleanly segregated, vertically ordered assemblages. The pattern instead records in situ accumulation, with organisms living where they are found, or at most parautochthonous deposition, as in the case of lepidocyclinids abraded and fragmented within cross-bedded packstones of the inner ramp, where submarine dunes redistributed bioclasts produced within a single facies belt. Elsewhere, the excellent preservation of the shells, occurring in flat-bedded wackestones and packstones devoid of structures indicating coarse gravity flows, points to little or no transport at all.

Geography adds a further argument. The reply notes that no Oligocene platform carbonates exist in the region, removing any plausible local source from which reworked fossils could have been derived. The authors also push back on the sampling criticism with unusual specificity. The marl samples MARMO-1 and MARMO-2 were taken from a marl bed intercalated with the fossiliferous limestones and physically traced to Section III, two hundred metres away. Samples MARMO-3 to MARMO-5 come from marly beds that, although not continuously traceable, clearly underlie limestones laterally continuous with Section III, with no Quaternary cover or debris obscuring the relationships. A fifth sample, MARMO-M1, was collected from a marl bed in Section V that can be visually traced to Section IV. The team acknowledges that Quaternary debris does hamper correlation between the eastern and western sectors of the Marmolance, which is why they did not attempt bed-to-bed matching, but they insist that this limitation does not undermine the combined stratigraphic ranges of the foraminiferal genera, since parts of the eastern sections demonstrably postdate the Burdigalian–Langhian transition while western sections postdate the Langhian–Serravallian boundary.

The dispute also touches on one of the grandest questions in Mediterranean palaeobiogeography: how did Nummulites, a genus long thought to have vanished from the region, persist into the Langhian of southeastern Spain? The reply clarifies that the team never proposed an evolutionary link between their Spanish fossils and the modern Indo-Pacific species Nummulites venosus, nor a direct migration route to Southeast Asia. But they do address the timing of the Indian Gateway, the oceanic connection between the Mediterranean and the Indian Ocean. Citing work by Bialik and colleagues, they note that the final closure of that gateway occurred around 13.8 million years ago, at the base of the Serravallian, after Nummulites had already disappeared from Marmolance. Before closure, currents flowed eastward through the gateway, meaning no closed barrier would have prevented the genus from spreading out of the Mediterranean during its final chapter there.

Beneath the technical exchanges lies a challenge with consequences far beyond one Spanish hillside. Papazzoni and colleagues argued that the proposed survival of larger benthic foraminiferal species over ten to fifteen million years is implausible, given that typical Cenozoic species last only two to three million years. The reply turns that logic on its head. If the fossils genuinely occur in situ within chronostratigraphically well-constrained Middle Miocene deposits, then it is not the Spanish succession that is wrong, but the calibration of the Shallow Benthic Zones, the standard biozonation scheme for dating Mediterranean shallow-water carbonates, first proposed by Cahuzac and Poignant in 1997. That scheme’s own authors admitted their correlation with the standard chronostratigraphic scale was provisional and open to revision. If the Marmolance record stands, ages assigned to rocks across the Mediterranean on the basis of these zones may need systematic reassessment, a prospect with implications for oil exploration, groundwater studies and any research built on the timing of Miocene shallow-marine deposits.

Scientific controversy of this kind is how the discipline advances. Formal comments and replies, peer reviewed and published side by side, force each camp to sharpen its evidence, and the Marmolance debate exemplifies the process at its most rigorous: quantitative facies analysis, statistical testing, field-traceable sampling and careful reasoning about sedimentary processes. Whether the larger benthic foraminifera of Granada ultimately rewrite the Miocene timeline or vindicate the existing zonation, the resolution will demand exactly what both sides have brought to the table, meticulous fieldwork and a willingness to test cherished assumptions against the rocks themselves. For now, the tiny coin-shaped shells of the Sierra de Marmolance remain what they have been for fifteen million years, silent witnesses to a vanished seaway, and newly vocal participants in one of micropalaeontology’s liveliest arguments.

Subject of Research: Chronostratigraphic ranges of Early–Middle Miocene larger benthic foraminifera in the Sierra de Marmolance, southeastern Spain

Article Title: Reply to Papazzoni et al.'s 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: Bolivar-Feriche, M., Reolid, J., Aguirre, J., Bassi, D., & Braga, J. C. (2026). Reply to Papazzoni et al.'s 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(2), 577-579. https://doi.org/10.5194/jm-45-577-2026

Image Credits: AI Generated

DOI: 10.5194/jm-45-577-2026

Keywords: larger benthic foraminifera, Miocene, biostratigraphy, Nummulites, lepidocyclinids, Risananeiza, planktonic foraminifera, carbonate ramp, reworking, Shallow Benthic Zones, Sierra de Marmolance, Mediterranean palaeobiogeography