The base is defined as the first appearance of the trilobite Glyptagnostus reticulatus around  million years ago. The top, or the base of the Jiangshanian is defined as the first appearance of the trilobite Agnostotes orientalis around  million years ago.
The base is defined as the initial appearance of the trilobite Glyptagnostus reticulatus approximately  million years ago. The top, or the base of the Jiangshanian, is defined as the first appearance of the trilobite Agnostotes orientalis around  million years ago.