Stage 5 of the Cambrian is the first stage of the 3rd series of the Cambrian (or Middle Cambrian). Its lower boundary has not been formally defined by the ICS yet. The most promising definition is the first appearance of either the trilobite species Oryctocephalus indicus or Ovatoryctocara granulata which is currently estimated to be around million years ago. The end of Cambrian Stage 5 and the beginning of the Drumian stage is marked by the first appearance of the trilobite Ptychagnostus atavus around million years ago.