Latest Proterozoic plankton from the Amadeus Basin in central Australia

Abstract

The plankton of the Proterozoic is preserved mainly as microfossils known as acritarchs, most of which are considered to be cysts of eukaryotic algae. In recent studies of the diversity of Proterozoic and early Palaeozoic acritarchs, a gradual increase in diversity from the Middle into the Late Proterozoic has been shown to be followed by a sharp decrease in diversity in the latest Proterozoic (Ediacarian or Vendian) and then a rise again in the Early Cambrian^1,2. These observations have been interpreted in terms of the evolutionary diversification of eukaryotic algae and the ecological effects of the pre-Ediacarian glaciation. Occasional discoveries of complex acritarchs in Ediacarian rocks^3-6 have raised some doubts about these interpretations, but more recent work seems to have supported this view⁷. Here we report the discovery of a diverse assemblage of large and morphologically complex acritarchs from the Ediacarian age upper Pertatataka Formation in the Amadeus Basin of central Australia. This, with a recent report of similar fossils from the upper Sinian of China⁸, provides a significant new perspective on the history of the plankton. It is now necessary to suggest an earlier radiation, at least in off-shore environments, or to question the reality of the postulated decrease in diversity. In addition, there may well have been an extinction event, late in the Ediacarian. Neither of these phenomena has been recognized previously.