TheFrancevillian biota (Also referred to asGabon macrofossils,Gabonionta orFrancevillian group fossils) are a collection of 2.1-billion-year-oldPalaeoproterozoic macroscopic structures, controversially suggested to be fossils, known from theFrancevillian B Formation in Gabon, ablack shale province notable for its lack of any noticeablemetamorphism.[1] The structures have been postulated by some authors to be evidence of the earliest form ofmulticellular life, and ofeukaryotes.[1][2] They were discovered by an international team led by Moroccan geologistAbderrazak El Albani, of theUniversity of Poitiers, France. While they have yet to be assigned to a formaltaxonomic position, they have been informally and collectively referred to as the "Gabonionta", including by theNatural History Museum Vienna in 2014.[3] The status of the structures as fossils has been questioned, and they remain a subject of debate.[4][5]
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The structures are up to 17 centimetres (6.7 in) in size.[6][7] They form flattened disks with a characteristicmorphology, including circular and elongated specimens. A spherical to ellipsoidal central body is bounded by radial structures. The structures show three-dimensionality and purportedly coordinated growth.[6]
A newer 2014 study by El Albani et al. describes multiple types of structures with different morphologies. There are convoluted tubes, and "string of pearls"-like structures that terminate in a "flower". This is similar todictyostelidslime molds,amoebal organisms that form multicellular assemblies to migrate. However, the structures cannot simply be dictyostelids as dictyostelids are not marine organisms. Among known fossils, theEdiacaranNemiana andBeltanelloides are most similar when compared to the "string of pearls".[1]
In 2023, more structures were studied by El Albani and colleagues, which were characterized by the authors aseukaryotes. They appear to be flattened lenticular disks reaching up to 4.5 cm in diameter, with a chambered interior surrounded by a notched ridge about 1/6th of the diameter in width. The authors hypothesized this to play a role in their movement through the water column, as they suggested the organisms were likelyplanktonic. The structures were found to have an unusual concentration ofzinc compared to the surrounding sediments, an element performing key functions in eukaryote biochemistry.[2]
The findings come from shales of theFranceville basin with a high density of up to 40 structures per square meter. The authors proposed that the organisms survived at the bottom in shallow sea water in colonies. Thegeochemistry of the site indicates that the structures formed in sediment under an oxygenated water column of aprograding delta, and if they were biological might have engaged inaerobic respiration.[6]
In describing the structures, El Albani and colleagues described them as colonial organisms with possible affinities toeukaryotes, akin tomicrobial mats, albeit unlike any known structures in the fossil record, yet noting the complexity of the structures and presence ofsterane as suggestive of possible eukaryote identity. In a concurrent news report inNature, paleontologistPhilip Donoghue of Bristol University advocates a more conservative approach pending further evidence before calling them eukaryotes.[citation needed]
Another view, held byYale'sAdolf Seilacher, interprets the structures as not organisms at all, but ratherpseudofossils of inorganicpyrites.[8] El Albani and colleagues (2014) explicitly disputed Seilacher's interpretation.[1] A 2016 study of similar structures in Michigan, around 1.1 billion years old found them to beconcretions, which the authors suggested cast doubt on the biogenicity of the Francevillian structures.[9] In a 2017 review paper Emmanuelle Javaux and Kevin Lepot stated that the biogenic nature of the macroscopic structures was "questionable".[4] Miao et al. 2019 stated that due to the "simple morphology and lack of diagnostic features, their eukaryotic affiliation still remains uncertain".[10] A 2023 review suggested that the structures were potentially artifacts ofdiagenesis, and that reliably distinguishing between biogenic and abiogenic structures inPaleoproterozoic rocks could be "extremely difficult", and therefore the Francevillian Biota and other supposed multicellular fossils of a similar age "currently fail to pass the stringent criteria for these structures to be viewed as bona fide fossils".[5] A 2023 isotopic analysis of the structures found that they were enriched inzinc,cobalt andnickel isotopes, with the zinc being preferentially enriched in light isotopes, which the authors suggested could represent eukaryotic metabolism. However they noted that the Francevillian Biota is still 400 million years older than is currently widely accepted for the earliest known eukaryotes.[11] Ernest Chi Fru and colleagues (including El Albani) argued in 2024 that there is evidence of nutrients conducive to animal life in the deposits.[12]
The identity of the [Francevillian biota] macrostructures remains unknown and their biogenicity is questionable
