New species of the conodont Genus "Hindeodus" and the conodont biostratigraphy of the Permian-Triassic boundary interval

Abstract

Four new species of the conodont genus 'Hindeodus', 'Hindeodus eurypyge' sp. nov., 'Hindeodus inflatus' sp. nov., 'Hindeodus' sp. nov. A and 'Hindeodus' sp. nov. B, are described from the Permian–Triassic transition in South China. Our study confirms the first appearance of 'Hindeodus parvus' at the GSSP level, base of bed 27c at Meishan. However, at Shangsi the first occurrence of 'H. parvus' is about 4.5 m above the event boundary. Analysis of conodont biostratigraphy of the Meishan D section and the Shangsi section suggest significant differences between the two sections. These include the absence of 'H. changxingensis' Wang from the Shangsi section and the approximately 4.5 m of the Shangsi section that contains 'H. priscus' (Kozur), H. latidentatus (Kozur) and 'H. eurypyge' n.sp. below the first occurrence of 'H. parvus'. These differences may be accounted for most easily by suggesting that there is a minor depositional hiatus at the Permian–Triassic boundary GSSP level as based on the first appearance of the conodont 'Hindeodus parvus' in Meishan section D. Taxonomic re-evaluation of 'Hindeodus Pa' elements indicates that species of the genus can be broadly separated into two groups based on the morphology of the posterior portion of the element and on growth patterns. The stable Pa element morphology of 'Hindeodus', first developed in the Carboniferous, was replaced by a complex of rapid evolutionary change in the latest Permian and Early Triassic, with as many as 11 valid species of the genus in the Permian–Triassic boundary interval, which are probably descendants of only two species, 'H. typicalis' and 'H.' n.sp. B. We suggest that the dramatic change in conodont biofacies observed at the boundary in South China from 'Neogondolella'-dominated faunas to 'Hindeodus'-dominated faunas was caused by the introduction of a high component of silt, beginning in bed 27 at Meishan and bed 28 at Shangsi, that tipped the environmental balance in favor of 'Hindeodus' and 'Isarcicella' over 'Neogondolella' ('Clarkina') species. We contend that 'Hindeodus' species were adaptable to higher levels of turbidity than 'Neogondolella'('Clarkina') species and hence at Meishan and Shangsi it was not a matter of a drastic increase in the abundance of 'Hindeodus', but an exclusion of 'Neogondolella'.