THE EDIACARA BIOTA: NEOPROTEROZOIC ORIGIN OF ANIMALS AND THEIR ECOSYSTEMS

Abstract

The Ediacara biota (575–542 Ma) marks the first appearance of large, architecturally complex organisms in Earth history. Present evidence suggests that the Ediacara biota included a mixture of stem-and crown-group radial animals, stem-group bilaterian animals, "failed experiments" in animal evolution, and perhaps representa-tives of other eukaryotic kingdoms. These soft-bodied organisms were preserved under (or rarely within) event beds of sand or volcanic ash, and four distinct preservational styles (Flinders-, Fermeuse-, Conception-, and Nama-style) profoundly affected the types of organisms and features that could be preserved. Even the earliest Ediacaran communities (575–565 Ma) show vertical and lateral niche subdivision of the ses-sile, benthic, filter-feeding organisms, which is strikingly like that of Phanerozoic and modern communities. Later biological and ecological innovations include mobility (>555 Ma), calcification (550 Ma), and predation (<549 Ma). The Ediacara biota abruptly disappeared 542 million years ago, probably as a consequence of mass extinc-tion and/or biological interactions with the rapidly evolving animals of the Cambrian explosion.