Controlled hydroxyapatite biomineralization in an~810 million-year-old unicellular eukaryote

Biomineralization marks one of the most significant evolutionary milestones among the Eukarya, but its roots in thefossil record remain obscure. We report crystallographic and geochemical evidence for controlled eukaryotic bio-mineralization in Neoproterozoic scale microfossils from the Fifteenmile Group of Yukon, Canada. High-resolutiontransmission electron microscopy reveals that the microfossils are constructed of a hierarchically organized interwo-ven network of fibrous hydroxyapatite crystals each elongated along the [001] direction, indicating biological controlover microstructural crystallization. New Re-Os geochronological data from organic-rich shale directly below the fossil-bearing limestone constrain their age to <810.7 ± 6.3 million years ago. Mineralogical and geochemical variations fromthese sedimentary rocks indicate that dynamic global marine redox conditions, enhanced by local restriction, mayhaveledtoanincreaseindissolvedphosphateinporeandbottom waters of the Fifteenmile basin and facilitatedthe necessary geochemical conditions for the advent of calcium phosphate biomineralization.

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