Cambrian–Ordovician extinction event

[3] The emplacement of the Namaqualand–Garies dykes in South Africa has been dated to 485 mya, the time at which the Cambrian–Ordovician extinction event occurred, although there remains no unambiguous evidence of a causal relationship between this volcanism and the biotic turnover.

[1] The middle Cambrian to early Ordovician is characterized by persistent elevated extinction rates that are thought to have been maintained by anoxic conditions.

[6] Soft-body fossils with morphology characteristic of the Cambrian have been uncovered in Morocco, dated 20 million years post-extinction.

The 2010 paper by Roy, Orr, Botting, and their collaborators that announced the discovery suggests that Cambrian species persisted into the mid-Paleozoic.

They argue that what had been interpreted as a Cambrian-Ordovician extinction is instead an artifact resulting from a gap in the stratigraphic record.