TRILOBITE FAUNA FROM THE LOWERMOST SILURIAN OF MEITAN,GUIZHOU AND ITS IMPLICATIONS

The Rhuddanian(Llandovery, Silurian)includes the survival and recovery intervals respectively after the end-Ordovician mass extinction.The marine environment during the earliest Silurian was dominated by deeper-water,commonly anoxic conditions and sustained transgression,so shelly facies of this time interval are rarely known in the Gondwana and periGondwana regions. However, in the upper Yangtze region of South China paleoplate,some shelly facies are well-developed(e.g.the Wulipo Bed and the Niuchang Formation).The trilobite fauna documented in this paper provides a unique window for investigating trilobite macroevolution in South China during the Late Ordovician and early Silurian.Trilobite fossils were collected from the Wulipo Bed(middle Rhuddanian)and the Niuchang Formation(upper Rhuddanian) at Yanping and Gaojiang sections of Huangjiaba town, Meitan County, northern Guizhou,including 17 species of 15 genera(subgenera),11 families and 7 orders, amongst which five macroevolutionary types could be recognized,i.e.the declining survivors,the increasing survivors,the Lazarus survivors,the new arrivals and the Dead Clade Walking(DCW).Different types of trilobites have different kinds of survival strategies facing the crisis.Declining survivors and Lazarus survivors are major source of biological evolution after the mass extinction,to a certain extent,they influence the process of the biological evolution of the entire ecosystem. New arrivals mark the improvement of the environment after the mass extinction and the beginning of the trilobite recovery interval.

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