Diversity of organic-walled microfossils in the phosphates of the ca. 1 Ga Diabaig Formation, Torridon Group, NW Scotland

Precambrian organic-walled microfossils preserved in fine-grained
sedimentary rocks constitute the earliest fossil record of eukaryotic
life. The Mesoproterozoic-Neoproterozoic transition coincided with major
innovations in the evolution of early eukaryotes, including the radiation
of crown-group lineages, represented in these rocks by candidate red
algae, green algae, and fungi. However, the diversity of these early
eukaryotes is yet to be fully explored. Here, we present a systematic
description of the microfossil assemblage preserved in exceptional detail
within sedimentary phosphatic nodules and bands in the Diabaig Formation
of the ca. 1 Ga Torridon Group of northwest Scotland. Recent work has
highlighted the lacustrine or estuarine nature of its depositional
environment and confirmed that these fossils may include the oldest known
non-marine eukaryotes. We identify 11 morphotaxa from new collected
material, including the new species Minimarmilla multicatenaria gen. et
sp. nov, two undoubted eukaryotes, and two probable eukaryotes. The latter
include Pterospermopsimorpha sp., and a new network-forming unnamed taxon.
These microfossils present an important window on eukaryotic
diversification in non-marine aquatic environments during the
Mesoproterozoic–Neoproterozoic.