Diversity, paleobiology and ecology of Organic-walled Microfossils from the Proterozoic of Arctic Canada, and implications for early eukaryotic evolution.

• Main Author: Loron, Corentin
• Other Authors: Javaux, Emmanuelle
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ULiège - Université de Liège 2020
• Subjects: eukaryotes; Proterozoic; Canada; Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Arctic; Dismal Lakes
• Online Access: https://orbi.uliege.be/handle/2268/252625; https://orbi.uliege.be/bitstream/2268/252625/1/ORBI%20LORON%20C%20thesis.pdf

Understanding the appearance and evolution of Life on our Planet (and elsewhere?) requires multidisciplinary approaches intersecting, notably, biology, geology, chemistry and astronomy. Studies of Earth deep times provide insights on the early hydrosphere, atmosphere and geosphere which influenced the development of the early biosphere. Conversely, the transition from prebiotic chemistry to life and subsequent biological changes (prokaryotic then eukaryotic photosynthesis, rise of eukaryotes, appearance of crown-groups, …) also played a role in modifying our young planet. This study focuses on a fundamental period for the diversification of Life on earth, the Proterozoic, that span from 2500 to 541 Ma. The total diversity of organic-walled microfossils present in two unmetamorphosed sedimentary successions from the northwestern Canada was investigated: The Dismal Lakes Group and the lower Shaler Supergroup. These successions represent more than 700 million years of earth history (from 1600 to 900 Ma) and preserve beautiful and abundant microfossils, especially numerous taxa of eukaryotes. This thesis demonstrates that the major diversification of eukaryotes observed in the fossil record at ~800 Ma has, in fact, started earlier and was more gradual. Eukaryotes were diversified by the early Mesoproterozoic and crown groups might have already appeared by then. New and earlier evidence for eukaryovory permits to suggest that predation was probably a powerful driver of this diversity rise. By combining classical paleontological approaches with spectroscopic and ultrastructural analyses, a new candidate of crown-group eukaryote, Ourasphaira giraldae could be proposed. This microfossil, recognized as an early fungus, provides new insights into crown-group diversification in the Proterozoic but also a new calibration point for molecular clock estimates of early eukaryotic evolution, and in particular of the Opisthokontes. Collectively, these studies show that northwestern Canada is an exceptional window on early ...