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Cambrian Stage 4
Cambrian Stage 4 is the still unnamed 4th stage of the Cambrian and the upper stage of the 2nd Cambrian series. It follows the 3rd stage and lies below the Cambrian Stage 5. The lower boundary has not been formally defined by the International Commission on Stratigraphy yet. One proposal is the first appearance of two trilobite genera, ''Olenellus'' or ''Redlichia''. Another proposal is the first appearance of the trilobite species ''Arthricocephalus chauveaui''. Both proposals will set the lower boundary close to million years ago.〔(【引用サイトリンク】url=https://engineering.purdue.edu/Stratigraphy/gssp/index.php?parentid=77 )〕 The upper boundary corresponds to the beginning of Cambrian Stage 5 which also has not been formally defined yet. Proposals are the first appearances of the trilobite species ''Oryctocephalus indicus'' or ''Ovatoryctocara granulata'', dated at approximately million years ago.
==Naming==
The International Commission on Stratigraphy has not named the 4th stage of the Cambrian yet. In the widely used Siberian nomenclature stage 4 would overlap with parts of the Botomian and Toyonian.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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