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Fossil traces found in Gabon dating back about 2.1 billion years suggest the existence of a group of unique cells that have come together to form a multicellular organism similar to a slug that crossed the mud in search of a more favorable environment.
Reconstructions of string-shaped structures – named Gabonionta – from the Francevillian site in Gabon; the white and yellow arrows indicate the string-shaped specimens and the microbial mats, respectively: (A) volume rendering showing the external surface of straight structures; inset (B) shows the widening of a rope ending with a pyrite crystal (black arrows); (C) rendering the outer surface volume showing a weakly sinuous string; (D) rendering of the outer surface volume, frame indicating the position of the subvertical tubes; (E) outer volume transparencies of the same specimen as in D, side view showing the wire-like specimens within the host rock; frame indicates the position of the sub-vertical tubes; (F and G) transparent outer volume of the same sample as in D and E at different heights of the sample; (H) paired contorted chains; the box indicates the part (cross section) represented in I; (I) Virtual cross-section of twisted cords, a black arrow indicates pre-compactional deformation of silty shale slides. Scale bars – 1 cm. Image credit: El Albani et al, doi: 10.1073 / pnas.1815721116.
"The preservation of fossil traces, or traces of fossils, suggests that multicellular organisms that could move to reach food resources already existed 2.1 billion years ago, or more than 1.5 billion years ago. years older than previously thought, "said Professor Kurt Konhauser of the University of Alberta. , co-author of the study.
Traces of fossils have been discovered on the site of Franceville in the province of Haut-Ogooué in Gabon, Africa.
Preserved as tubular structures, they have a width of 6 mm and a length of 1.7 cm in the sedimentary layers and are probably the result of old mucus trails left by a multicellular life, such as amoeboid cells modern looking for food.
"A detailed 3D analysis using a non-destructive X-ray imaging technique, combined with geometric and chemical dating, revealed that the fossils belonged to an organism that probably spent most of its time in oxygenated water, and was therefore dependent on oxygen "paleontologists said.
"Near these tubular structures were fossilized microbial biofilms that were used as pasture for these organisms."
Rendering of volume showing the continuity between the morphologies of the leaf and the rope in a single specimen. Scale bars – 1 cm. Image credit: El Albani et al, doi: 10.1073 / pnas.1815721116.
"It is plausible that the organisms behind this phenomenon have moved in search of nutrients and oxygen produced by bacteria mats at the sea floor interface- water, "said co-author, Ernest Chi Fru, a researcher at Cardiff University.
"This seabed environment was calm and shallow at the time, and rich in oxygen after the first wave of the great oxygenation event, which had started about 300 million years ago," said the first author, Abderrazak El Albani, CNRS and the University of Poitiers.
"The current increase in the oxygen content of the oceans could have played an important role in providing the energy needed for the metabolism and development of these multicellular organisms, as well as their movement."
"The question that arises from this research is therefore why it takes us 1.5 billion years to see similar characteristics in the rock record. We will not see anything like this before 585 million years ago, "said Professor Konhauser.
Some scientists assume that this early appearance of complex life is extinct because of an environmental factor.
Others suggest that similar fossilized tracks may have existed but have not been preserved or have simply gone unnoticed elsewhere.
"The whole community is right to be skeptical about the interpretation," said Professor Konhauser.
"However, one of the current paradigms relating to the evolution of multicellular organisms is the availability of oxygen.There are 2.1 billion years ago, there was no shortage of oxygen in shallow marine waters. "
The search appears in the Proceedings of the National Academy of Sciences.
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Abderrazak El Albani et al. The motility of organisms in a oxygenated shallow marine environment, 2.1 billion years ago. PNAS, published online February 11, 2019; doi: 10.1073 / pnas.1815721116
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