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Early fossil eukaryotes were benthic aerobes.

Maxwell A Lechte^1,2, Leigh Anne Riedman^3,4, Susannah M Porter⁵

¹Department of Earth and Planetary Sciences/Geotop, McGill University, Montreal, Quebec, Canada. maxlechte@gmail.com.

|May 20, 2026

Summary

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Area of Science:

Paleontology
Geochemistry
Sedimentology

Background:

The origin of eukaryotic cells is crucial for understanding complex life's evolution.
The environmental conditions during early eukaryote evolution remain largely unclear.

Purpose of the Study:

To reconstruct the ancient habitats of the earliest known fossil eukaryotes.
To investigate the environmental context of eukaryote evolution using geological records.

Main Methods:

Integrated analysis of paleontological, sedimentological, and geochemical data.
Examination of fossil eukaryotes from approximately 1.75 to 1.4 billion years ago.
Reconstruction of depositional environments ranging from coastal to offshore settings.

Main Results:

Fossil eukaryotes were found in diverse environments but predominantly in those with oxygenated bottom waters.
The distribution suggests early eukaryotes were aerobic (obligate, facultative, or microaerophilic) and likely possessed mitochondria.
Their scarcity in anoxic samples indicates a predominantly benthic existence, unlike planktonic organisms.

Conclusions:

Early eukaryotes were likely restricted to oxygenated benthic habitats throughout much of the Proterozoic eon.
Expansion into planktonic habitats occurred later, during the Neoproterozoic era (1-0.54 billion years ago).
This ecological shift may explain discrepancies in fossil and molecular data and the rise in eukaryote diversity during the Neoproterozoic.