Morphological and ecological complexity in early eukaryotic ecosystems

Molecular phylogeny and biogeochemistry indicate that eukaryotes differenti ated early in Earth history. Sequence comparisons of small-subunit ribosoma l RNA genes suggest a deep evolutionary divergence of Eukarya and Archaea(1 ); C-27-C-29 steranes (derived from sterols synthesized by eukaryotes) and strong depletion of C-13 (a biogeochemical signature of methanogenic Archae a) in 2,700 Myr old kerogens independently place a minimum age on this spli t(2,3). Steranes, large spheroidal microfossils, and rare macrofossils of p ossible eukaryotic origin occur in Palaeoproterozoic rocks(4-6). Until now, however, evidence for morphological and taxonomic diversification within t he domain has generally been restricted to very late Mesoproterozoic and Ne oproterozoic successions(7). Here we show that the cytoskeletal and ecologi cal prerequisites for eukaryotic diversification were already established i n eukaryotic microorganisms fossilized nearly 1,500 Myr ago in shales of th e early Mesoproterozoic Roper Group in northern Australia.