NEW REPORT OF SHALE-HOSTED ORGANIC-WALLED MICROFOSSILS FROM THE EARLY MESOPROTEROZOIC DISMAL LAKES GROUP IN ARCTIC CANADA

The oldest occurrences of eukaryotic organisms in the fossil record are reported from shale units of the late Paleoproterozoic and early Mesoproterozoic of Australia and China. These specimens display conspicuous surface ornamentations or processes, unambiguously indicating a eukaryotic origin. Although their crown or stem group affiliation remain unclear, there are providing a minimum age for FECA, the First Eukaryotic Common Ancestor. However, it is possible that the Total group eukaryotes were present earlier, perhaps even as early as the Archean.

For the development of eukaryotic organisms in oceans, the Mesoproterozoic is an important era. The advent of eukaryotic photosynthesis, osmotrophy, multicellularity, and predation during the Mesoproterozoic, have allowed eukaryotes to thrive in taxonomy, metabolism, and ecology. Nevertheless, despite these biological innovations, their fossil record remains scarce before the late Mesoproterozoic.

We report a new assemblage of organic-walled microfossils from the 1590–1270 Ma Dismal Lakes Group in Canada. The assemblage, comprising 25 taxa, contains 11 morphospecies identified as eukaryotes, including the new species Dictyosphaera smaugi, a relatively high diversity for this period. Although redox conditions were fluctuating in the Mesoproterozoic, the deposition in a photic shallow tidal-influenced environment suggests occasional aerial exposure and implies that the some of these early eukaryotes may have lived in slightly oxygenated waters. These setting imply that they may have resisted low, but present, oxidative stress, and could have already possessed mitochondria.

The diversity of eukaryotic forms in this succession is comparable to slightly older assemblages from China and is higher than worldwide contemporaneous assemblages. This new evidence supports the hypothesis of an earlier diversification of eukaryotes in the Mesoproterozoic.