Emsian (Lower Devonian) conodonts from the Lufengshan section (Guangxi, South China)

The Lufengshan section (Guangxi, South China) is one of the best representative sections of the Xiangzhou facies (benthic facies), from which a few Emsian conodont studies have been accomplished in the past. In this paper, we present conodonts from the Upper Member of the Ertang Formation at the Lufengshan section. The conodont fauna is characterised by a distinctly low diversity with only six species reported and is assigned to the nothoperbonus Zone. Ozarkodina'? chenae, O.'? wuxuanensis and Polygnathus praeinversus are newly described species herein. A comparison of the contemporaneous conodont faunas between the Lufengshan, Liujing and Daliantang sections indicates that the conodont biodiversity during the time of the nothoperbonus Zone in South China is mainly bathymetrically controlled. Moreover, P. praeinversus, which was previously thought to be transitional between P. inversus and P. serotinus, is interpreted to represent an intermediate form between P. nothoperbonus and P. inversus on the basis of stratigraphical and morphological analyses. The outline of the basal cavity of this new polygnathid species better documents the evolutionary process of the inversion of the basal cavity of Polygnathus: the basal cavity in the middle part of the platform starts to invert on the inner side at first, whereas the flat or slightly elevated outer flank of basal cavity is laterally extended to form a shelf-like protuberance on the outer side of the pit.