Tremadocian
Key events in the Ordovician
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Key events of the Ordovician Period.
ICS approved stages.
Axis scale: millions of years ago.
ICS approved stages.
Axis scale: millions of years ago.
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian stage it forms the Lower Ordovician epoch. The Tremadocian lasted from 485.4 ± 1.9 to 477.7 ± 1.4 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the GSSP section in Newfoundland.