Eukaryotes evolved in the Proterozoic eon. The oldest known probable eukaryote is "Grypania", a coiled, unbranched filament up to 30 mm long. The oldest "Grypania" fossils come from an iron mine near Negaunee, Michigan. The fossils were originally dated as 2100 million years ago, but later research showed the date as about 1874 million years ago. "Grypania" lasted into the Mesoproterozoic era.