Eukaryotic evolution over the last 1.8 billion years

https://www.science.org/doi/10.1126/science.adm9137
The article may be paywalled.  They claim fossil evidence over the last 2 billion years, and have placed over 13,000 "events" along this timeline.
QUOTE:
Editor’s summary
Fossil data from the Phanerozoic eon provide insight into long-term changes in global biodiversity and how it has been shaped by evolution, environmental change, and species interactions. Insights from the earlier Proterozoic eon are relatively lacking because of historic gaps and inconsistencies in data. Using recent advances in data and analytical methods, Tang et al. produced updated estimates of eukaryote diversity across the Proterozoic. They found a gradual increase in species richness during the “Boring Billion” pre-Cryogenian period, which is distinct from the higher diversity and dynamics of the later Ediacaran. Cryogenian glaciations appear to define this shift toward greater extinction and diversification rates. —Bianca Lopez
Structured Abstract
INTRODUCTION
The Proterozoic Eon [2500 to 539 million years ago (Ma)] in Earth history is marked by numerous transformative evolutionary, environmental, and tectonic events. However, a comprehensive quantification of Proterozoic eukaryote fossil diversity is lacking, hampering analysis of the global patterns and mechanisms of Earth-life coevolution in this important eon. Here we report a high-resolution analysis of the diversity and evolutionary dynamics of Proterozoic and early Cambrian (539 to 509 Ma) eukaryotes based on a global compilation of fossil data. This result provides opportunities to test various hypotheses about the coevolution of the Proterozoic biosphere and geosphere.
RATIONALE
The graphic correlation program Constrained Optimization (CONOP) was used to optimize correlations across fossiliferous sections and to develop the best-fit composite sequence of the first and last appearances of fossil species. The CONOP computation was supplemented by geologically correlatable events and time-calibrated by radiometric ages. The diversity of Proterozoic and early Cambrian eukaryote fossils was then calculated from the composite sequence, with various sensitivity tests to assess the impact of uncertain age estimates, ambiguous taxonomic assignments, putative eukaryotic affinities, and fossil sampling biases on the estimate of global species richness.
RESULTS
The results confirm the Cryogenian Period (~720 to 635 Ma) as a major divide in Proterozoic eukaryote evolution. The species richness of eukaryote fossils remained consistently low and relatively static with small-scale fluctuations before the Cryogenian but increased rapidly and experienced more dynamic changes in the Ediacaran (~635 to 539 Ma) and early Cambrian periods. Similarly, species origination, extinction, and turnover rates were low before the Ediacaran Period but were much higher and showed greater variation afterward. The accelerated evolutionary dynamics are exemplified by the rapid rise and fall of various groups of Ediacaran eukaryotes, including the rapid decline of a group of Ediacaran microfossils known as the Doushantuo-Pertatataka acritarchs (DPAs) after the Gaskiers glaciation (~581 to 580 Ma), the subsequent diversification of the Ediacara biota that is represented by Ediacara-type macrofossils and includes some of the earliest known macroscopic animals, and double extinctions at ~551 Ma and 542 to 539 Ma that led to the demise of the Ediacara biota.
CONCLUSION
The quantitative results provide critical insights into the coevolution of Earth and life in the Proterozoic Eon. The contrasting evolutionary patterns of eukaryotes before and after Cryogenian glaciations indicate that global glaciations played an important role in the macroevolution of Proterozoic eukaryotes. The static diversity pattern before the Cryogenian Period echoes the “Boring Billion” (~1800 to 800 Ma), which is characterized by stability in the global carbon cycles. Considering that major eukaryotic groups may have diverged in the “Boring Billion,” there must have been a long delay before Proterozoic eukaryotes rose to ecological and taxonomic dominance. In the Ediacaran Period, the rapid disappearance of DPAs that began during the Gaskiers glaciation represents the earliest mass extinction of eukaryotes in the Proterozoic Eon, probably due to global cooling. The rise of macroscopic animals and their traces coincided with the nadir of the Shuram excursion (574 to 567 Ma) that represents the largest perturbation to the carbon cycle in Earth history, indicating a possible causal relationship between oceanic oxygenation and the rise of macroscopic animals. The double extinctions in the late Ediacaran Period represent the first documented mass extinctions of animals. These evolutionary events highlight the complex interplay in the Proterozoic Earth-life system.
The first figure after the summary notes extinctions and species originations per half million year periods.  Both were likely less than 10 before 600 million years ago, and closer to zero than 10 for most of that time between 1.8 billion years ago and 600 million years ago.  The number of known species seems to be less than 100 during this time period, so it looks like they kept finding the same low number of species for a very long time with little increase after around 1.5 million years ago.  So the same species were fossilizing over a very long period of time.  There was a period of time between 1.4 billion and 1.1 billion years ago where new species and extinctions were near zero.
When does it become an issue in terms of what you can identify as eukaryotes in the fossil record?  Is it possible that there are species of eukaryotes that could not be identified as fossils that existed during this time period, and they are only counting the fossils that can be identified as eukaryotes so they keep counting the same or similar species during an extended time period?
Ron Okimoto