Coiled carbonaceous megafossils from the Middle Proterozoic of Jixian (Tianjin) and Montana

Coiled carbonaceous impressions on bedding planes of the 1400 Ma Greyson Shale (Belt Supergroup) of Montana and the similarly aged Gaoyuzhuang Formation (Changcheng "System') of Tianjin are the oldest indubitable megafossils now known. They were first found by C.D. Walcott in the 1890's; recent discoveries have allowed a much fuller description and interpretation than was possible before. They are all included here in the taxon Grypania spiralis (Walcott) (Walter, Oehler, and Oehler, 1976). Previous interpretations have ranged from non-fossil to metazoan trace fossils, but they are considered here most probably to be eucaryotic algae. No cellular structure has been detected. A record of comparable megafossils of Middle and Late Proterozoic age is gradually being uncovered, consistent with other evidence that eucaryotes evolved at least 1.7 Ga ago. -Authors