New conodont fauna from the Floian (Lower Ordovician) Acoite Formation, Cordillera Oriental, Argentina

Abstract

This contribution reports a new species, Trapezognathus morenensis n. sp., from the upper levels of the Acoite Formation outcropping in the El Moreno area of the Cordillera Oriental, northwestern Argentina. This species occurs together with Trapezognathus diprion, Costiconus sp., Drepanodus arcuatus, Drepanoistodus costatus, D. forceps, D. pitjanti, Erraticodon patu, Gothodus costulatus, G. andinus, Kallidontus sp., Paltodus subaequalis, Parapanderodus cf. striatus, Paroistodus parallelus, Protopanderodus rectus, Zentagnathus argentinensis, Gothodus spp., and Drepanoistodontid gen. et sp. indet. Trapezognathus morenensis n. sp. exhibits intermediate characteristics between T. diprion and T. quadrangulum, and also displays a close relationship with early species of the genus Baltoniodus. The conodont assemblage allows for the identification of the Gothodus andinus and Trapezognathus diprion zones, indicating a middle to late Floian (Early Ordovician) age. In addition, the boundary between the Gothodus andinus Zone and the succeeding Trapezognathus diprion Zone is defined by the first occurrence datum of Trapezognathus diprion within the same stratigraphic section, representing the first documented instance of this boundary. The revision of associated taxa with reported Trapezognathus spp. suggests that the definition of the Floian–Dapingian boundary still requires verification in the Cordillera Oriental of Argentina.