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.