Llandovery (Silurian) conodont provincialism: An update based on quantitative analysis

Abstract

The Llandovery conodont provincialism is reassessed based on a larger dataset than that which was available in 1990. The study interval is divided into two time units, the ‘Pre-Telychian’ and Telychian. Three quantitative methods are adopted in the biogeographic analysis, including cluster analysis, non-metric multidimensional scaling, and minimum spanning tree. In the ‘Pre-Telychian’ interval, four provinces can be recognized, i.e., the North American-Baltic-Siberian, Timan-Severnaya Zemlya, Australian, and Yangtze provinces. However, only three provinces can be recognized in the subsequent Telychian interval. The Timan-Severnaya Zemlya Province existed also in this time interval, but Austria and Australia are combined with the ‘Pre-Telychian’ North American-Baltic-Siberian Province and form a new province, the Baltic-Austrian-Siberian-Australian-North American Province (BASAN Province), while Tibet and the ‘Pre-Telychian’ Yangtze Province form the Chinese Province.The conodont richness shows a latitudinal or temperature-dependent gradient. The conodont fauna was most diverse in the lower latitudes (tropical, arid and partly warm temperate climatic zones). However, the provincialism of the Llandovery conodont faunas demonstrates a longitudinal pattern, which cannot be the result of any latitudinal factors, such as temperature, but could be controlled by longitudinal factors, probably by the circulation of ocean currents. The circulation pattern can also explain the formation of the Telychian BASAN Province, which probably resulted from the Rheic and Panthalassa Ocean gyres. According to the conodont provincialism and the distribution of taxa, five types of conodont species can be recognized, including Limitedly distributed species, BASAN species, Equatorial species, Shallow-Sea Realm species, and Cosmopolitan species.The conodont fauna showed a significant change in provincialism from the Ordovician to the Silurian, i.e., from a latitudinal pattern to a longitudinal pattern. The Hirnantian glaciation may be one of the controlling factors which resulted in the reorganization of the conodont faunas and the change of their living habits and ecological requirement.