Drumian
Period
The Drumian is a stage of the Miaolingian Series of the Cambrian. It succeeds the Wuliuan and precedes the Guzhangian. The base is defined as the first appearance of the trilobite Ptychagnostus atavus around 504.5 million years ago. Wikipedia
Occurred: 504.5 million years ago - 500.5 million years ago
Epoch: Miaolingian
Lower boundary GSSP: Drumian section, Wheeler Shale, Utah, U.S.A. 39°30′42″N 112°59′29″W / 39.5117°N 112.9915°W
Lower GSSP ratified: 2006
Upper GSSP ratified: 2008