Bashkirian (Early Pennsylvanian, Carboniferous) Conodonts from the Shanglong Section, Southern Guizhou, South China

The Shanglong section in southern Guizhou, South China, was deposited in the platform margin to upper slope facies during the Carboniferous and Permian. From the lower Bashkirian to lower Moscovian of this section, a diverse and abundant conodont fauna has been recovered. The P1 elements of this fauna are dominated by Idiognathoides, with subordinate occurrences of Declinognathodus and Swadelina, among others. In total, 42 species and subspecies assigned to 13 genera were identified. Seven conodont zones are recognized, including the Bashkirian D. noduliferussensu lato, Id. sinuatus, Neognathodus symmetricus, “Streptognathodus” expansus M1, and “S.” expansus M2 zones, as well as the Moscovian Diplognathodus ellesmerensis and Mesogondolella donbassica−M. clarki zones. These zones can be correlated with those of the nearby Naqing and Luokun sections, as well as with zonations of Eastern Europe and North America. In addition, the nodose and ridged groups of the genus Idiognathoides are distinguished based on parapet ornamentation and symmetry of the P1 elements. Within the nodose group, Id. sulcatus sulcatus and Id. opimushave previously been considered conspecific due to morphological similarities. However, differences in platform morphology and stratigraphic distribution support their recognition as separate valid species. A possible evolutionary lineage, Id. macer-Id. sulcatus sulcatus-Id. opimus-Id. postsulcatus, has been proposed. As the typical representative of the ridged group, Id. sinuatus includes at least three distinct morphotypes. These findings lead to a revised understanding of the taxonomy and evolution of Idiognathoides.