a billion-year-old fossil isolated in Scotland

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A billion-year-old fossil discovered in the Highlands, Scotland, could stand as a “bridge” between single-celled and multi-celled organisms. This discovery also suggests that the first forms of terrestrial life developed in fresh water.

It is a discovery that we do not make every day. Sediments of the Torridonian sequence of the Highlands of northwestern Scotland harbor a wide array of microfossils, some documenting life in a non-marine environment several hundred million years ago.

Recently, a team from the University of Sheffield (United Kingdom) and Boston College (United States) isolated a new fossil even older in the Loch Torridon. Scientists were able to study these remains because of their exceptional conservation, allowing them to be analyzed at the cellular and subcellular level.

This body, formed there about a billion years, has just been named Bicellum Brasieri. Details of the study are published in the journal Current biology.

A bridge in the evolution of living things

The mature form of this organism, named Bicellum Brasieri, occurs as a spheroidal mass of mutually expressed cells surrounded by a peripheral layer of elongated sausage-shaped cells. The inner cell mass forms a stereoblast of roughly isodiametric cells with an average diameter of about 2.5 μm.

However, two populations of naked blast cells appear to exhibit incipient elongation, suggesting that they may migrate to the periphery of the cell mass. These simple morphogenetic movements could be explained by a differential cell-cell adhesion.

In a much simpler way, this organism could therefore be located somewhere between a unicellular life form and a multicellular life form. For the researchers, it seems reasonable to assume that B. Brasieri belongs to one of the lineages leading to one of the six clades developing today a complex multicellularity: animals, plants, floridophytic algae, brown algae, ascomycete fungi and fungi. basidiomycetes.

“We found a primitive spherical organism composed of an arrangement of two distinct cell types, the first step towards a complex multicellular structure. This is something that has never been described before in the fossil record ”, underlines Charles Wellman, main author of this work.

“The origins of complex multicellularity and the origin of animals are considered two of the most important events in the history of life on Earth”, he added. “Here, our discovery sheds new light on these two elements”.

Some elongated cells appear at the periphery of the cell mass. However, a clearly distinct epidermal layer is not yet established. Note that there is no apparent distinction between cell walls of either type of cell. Credit: Current Biology

This new finding also suggests that this development occurred in freshwater, rather than in the ocean. The team aims to continue research in these same repositories. The discovery of new and more interesting fossils could provide more information on the evolution of multicellular organisms.

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