The Ajax Limestone in the Northern Flinders Ranges includes a significant array of Lower Cambrian Archaeocyath fossils, replaced by quartz, exposed in ground-level limestones.
This fossil site on a low gibber-covered rise to the north of Beltana represents the most species-diverse archaeocyath locality worldwide, with a count of 82 species. One of seven sites in the Flinders Ranges currently under consideration for UNESCO World Heritage status, it provides a significant record of an extinct group of marine sponges (Phylum Porifera) that lived around 525 million years ago and played a dominant role in constructing the first reefs on Earth.
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