New types of microfossils may show how and when complex cells evolved

Scientists have long thought about how and when the evolution of prokaryotes – simple microorganisms that lack distinct cellular structures – into eukaryotes – microorganisms with complex structures such as the nucleus -. A collaborative research team from Tohoku University and the University of Tokyo may have provided some answers after discovering new microfossils dating back 1.9 billion years.

The Gunflint formation It crosses the northern part of Minnesota into Ontario, along the northwest shores of Lake Superior. The first microbial fossils were discovered there in 1954, with Gunflint’s microfossils now recognized as a “standard” in the field of life evolution.

However, since the 1970s, little research has been done on the diversity of Gunflint’s microfossils, and no conclusive evidence for eukaryotic microfossils has been reported.

In an effort to reassess the microfossils, the research team conducted a geological survey of the Gunflint Formation and collected microfossil-containing rocks. After investigating the three-dimensional shape and size distribution of the microfossils, they discovered five types of microfossils: colonial, ellipsoid, intracellular intracellular (ICI), and spinous and caudal types.

“Recently found is more effective,” he explains. Kohei Sasaki, Research Fellow at Tohoku Universityy. “Oval microfossils are similar to modern cyanobacteria, which evolved to improve their tolerance to harsh environments; while chemical analysis showed that ICI microfossils were full of nutrients.”

This provides evidence that microorganisms have evolved to store nutrients that can withstand environmental stress. Spiny and tail-bearing fossils show features useful for locomotion and intercellular nutrient transport, a morphological feature typical of eukaryotes.

“Although prokaryotic cells are large by definition, they have already developed eukaryotic functions,” Sasaki adds. This suggests that prokaryotes may have begun to diversify their functions and prepare for evolution before eukaryotes appeared 1.8-1.6 billion years ago.

The team speculates that the unique environment at the time facilitated the evolution of microbial forms. The collision of land masses and the formation of mountains accelerated weathering from the continent to the ocean. This increased nutrient supplies and raised sea water temperatures.

“Under these conditions, microorganisms may have diversified their morphology as a survival strategy, paving the way for the evolution of eukaryotes,” Sasaki concludes.

Sasaki and his team’s landmark discovery will help scientists determine the timing and factors that led to the evolution of prokaryotes into eukaryotes, providing not only geological significance, but also aid in the fields of life sciences and evolutionary biology.

the paper “Evolutionary diversification of ancient prokaryotes: new microfossil records in the 1.88 Ga Gunflint Formation.Posted in Precambrian research (2022). Material provided by Tohoku University.