Oldest fossil records of marine protists and the geologic history toward the establishment of the modern-type marine protist world

Abstract

The oldest marine protist fossil goes back 1.8 Ga (Statherian, Paleoproterozoic), and the oldest dinosterane biomarkers 1.6 Ga (Calymmian, Mesoproterozoic). The probable heterotrophic agglutinated microfossil appeared when marine metazoans appeared in the Ediacaran. Multichambered foraminifers appeared around the start of biomineralization in Small Shelly Fossils in the early Cambrian. The first fossilizable radiolarian polycystine is likely to have appeared in the period of the Cambrian Explosion. After the initial appearance period, the emergence of fossilizable skeleton formative ability was concentrated in five short geological time intervals: (1) the Middle to Late Devonian for calcareous benthic foraminifers; (2) the Carnian to the Rhaetian (Triassic) for the "switching on" of fossilizable dinoflagellate cysts, nannoliths, coccoliths and calcareous cysts, and probably the molecular appearance of diatoms; (3) the Toarcian-Aalenian Ages for diversified dinoflagellates and coccolithophores, the establishment of symbiosis in radiolarian Acantharia and the appearance of planktic lifestyle in foraminifers; (4) the Albian-Maastrichtian Ages for the rapid accumulation of coccolithophores, the start of skeletogenesis both in silicoflagellates and marine centric diatoms, molecular appearance of both araphid and raphid diatoms, and the appearance of fossilizable araphid diatoms; and (5) the middle to late Eocene for the appearance of fossilizable raphid diatoms and radiolarian colonial collodarians and the continuous occurrences of ebridians. The establishment of the modern-type marine protist world was concluded in the late Eocene by the appearance of collodarians, the continuous occurrences of ebridians, and the substituted silicon precipitation marine protists as diatoms.