THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their Ecosystems

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 representatives 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 sessile, 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 extinction and/or biological interactions with the rapidly evolving animals of the Cambrian explosion.