Fossils of the Ediacara Biota, first discovered and realised by the late Reg Sprigg AO in the Ediacara Hills and later discovered at many sites in the Flinders Ranges, north of Port Augusta and south of Marree. Ediacara fossils are unique as the oldest large and complex organisms on Earth, preserved as impressions in sandstone. They gave their name to the Ediacaran Period, the first new major time division to be defined in 120 years, and the first based on rocks in the Southern Hemisphere. The base of the Ediacaran is fixed as a point in rocks of the Flinders Ranges National Park, following a many decades of research on the fossils and rock formations of South Australia. Current research on Ediacara fossils is focused on excavating serial fossil seafloors in order to understand the ecology of these ancient marine communities.