Middle Ordovician

The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species Undulograptus austrodentatus around million years ago. It lasted for about 10.8 million years until the beginning of the Sandbian around million years ago. This stage of the Ordovician was marked by the beginning of the Andean-Saharan glaciation.

The Dapingian is the third stage of the Ordovician system and the first stage of the Middle Ordovician series. It is preceded by the Floian and succeeded by the Darriwilian. The base of the Dapingian (and the top of the Floian) is defined as the first appearance of the conodont species Baltoniodus triangularis which happened about million years ago. The Dapingian lasted for about 1.9 million years until about million years ago.

event of around 467 million years ago