The conodont Paroistodus horridus (Barnes and Poplawski) as a new biostratigraphical tool for the middle Darriwilian (Ordovician)

This contribution develops an analysis on the conodont Paroistodus horridus (Barnes and Poplawski) from several Argentine Precordilleran sections. From these collections, we have established that P. horridus occurs from the Lenodus crassus Zone to the Amorphognathus tvaerensis Zone (Darriwilian to early Sandbian). This study recognizes several primary morphological features of P. horridus which vary through the Darriwilian and three evolutionary morphological types can be identified: early form, middle form with two stages, and late form. The co-occurrence of index conodonts with the successive stages of this evolutionary development allowed a significant biostratigraphical value to be assigned for each different morphological type of P. horridus. Based on this information, we propose a detailed biostratigraphical control and correlation with equivalent strata from Canada, China, Australia, United States, Norway, and western Central Asia.