By Susan Milius
Tiny fossils a billion years old — the earliest ones yet found of complex cells outside the sea — give the first direct evidence that evolution in freshwater had already expanded beyond bacteria long before the first trilobite skittered through Paleozoic muck.
Fossilized bits less than a millimeter long from Scotland suggest that cells with nuclei were flourishing beyond the oceans, says Paul K. Strother of Boston College. Such cells distinguish one of the three major domains of life, the eukaryotes, which today range from elaborate microbes such as the schoolbook paramecium to all plants, fungi and animals.
The fossilized cells or masses of cells look eukaryotic because of features not known from bacteria, Strother and his colleagues report online April 13 in Nature.
For example, one fossil appears to be a mass with three lobes. Other finds show evidence of cell coverings splitting along a preformed biological zipper, or cells with protective coverings bearing complex patterns.