Study and Analysis on Extinction of the lower Cambrian Index fossil Bathynotus:For Instance Bathynotus kueichouensis from Kaili Formation,Guizhou

Bathynotus is the most important trilobite genus as the late Cambrian 2 series.It is widely distributed in three realms of Cambrian in the world and has very important significance for subdivision of Cambrian stratigraphy in the world.Bathynotus from Kaili Formation at Wuliu-Zengjiaya Section Balang Village,Jianhe County,Guizhou Province are extremely rich and preserved a complete sequence of ontogeny.After specimens from a stratigraphical interval examined,we confirm that Bathynotus was extinct suddenly on position of 51.60 m away from the base of Kaili Formation,at Wuliu-Zengjiaya Section.This position is only 1.20 m upward to the top of Cambrian 2 Series(that is,52.80 m away from the base of Kaili Formation).Here,we attempts to understand the process of extinction of Bathynotus of the lower part of Kaili Formation by methods of mathematic statistics for specimens collecting continuously little layers and fossil sequence change analysis.This research indicates the process of extinction is a gradual change,that is,Bathynotus distributed at Wuliu-Zengjiaya Section,close to the extinct position only were found mature no juvenile specimens.