Reexamination of the conodont apparatus of <i>Neostrachanognathus</i> based on natural assemblages from the Olenekian (upper Lower Triassic) “Toishi-type” siliceous claystone, Japan

Abstract Conodonts with conical elements that closely resemble Paleozoic species reappeared in the Early Triassic. The phylogeny, evolution, and paleoecology of these conodonts are poorly known. In this study, we describe a new species of Neostrachanognathus , N. koikei n. sp., one of the conical conodonts, and reconstruct the conodont apparatus of this species according to natural assemblages from the “Toishi-type” siliceous claystone of Japan. The apparatus of N. koikei consists of 15 elements, including two pairs of P, one pair of M, and four pairs of S elements, and a single S 0 element. Notable features include conical P 1 and P 2 elements and nine S elements that are similar in morphology to each other. The S elements of N. koikei are identified as belonging to the form species “ Neohindeodella aequiramosa ” Kozur and Mostler, 1970, specifically to the morphology occurring from the Spathian to the Anisian. Furthermore, S elements of the type species of Neostrachanognathus , N. tahoensis Koike, 1998, appear to correspond to “ Neohindeodella benderi ” (Kozur and Mostler, 1970). Therefore, from these S-element morphologies, we conclude that Neostrachanognathus belongs to the family Ellisoniidae. These conodonts with simplified elements flourished and were widely distributed throughout the world, from continental shelves to the open ocean, during the Early Triassic to the early Middle Triassic. UUID: http://zoobank.org/5e21971a-aac9-432c-8413-1994293867ab