The late Triassic was the time interval of greatest morphologic diversity for the conodont genera. Those short-ranging taxa, with distinctive shapes, often were represented by only a few species, and they have proved particularly useful, serving as excellent biostratigraphic keys (e.g., Paragondolella, Metapolygnathus, Epigondolella, and Misikella). The genus Metapolygnathus is regarded as characteristic of the Tuvalian, Lacian, and Alaunian. Its morphology has not been adequately investigated, and the species composition has been recognized only to a first approximation. The literature data on this problem are very contradictory (Hayashi, 1968; Kozur, 1972; Mosher, 1973; Budurov, 1977; Krystyn, 1980; Orchard, 1991).

I have recognized six species of Metapolygnathus in the Upper Triassic of Sikhote-Alin. This genus is defined in the paper by S. Hayashi's (1968) original diagnosis, aided by K. Budurov (1977). Those sources provided the basis for this chapter.

Phylogenetic relationships of the Metapolygnathus platform elements

The reconstructed organisms described as Metapolygnathus represent conodont elements that, along with the platform elements discussed here, contain such elements as cypridodelliform, hindeodelliform, chirodelliform, diplododelliform, prioniodelliform, and enantiognathiform structures (Buryi, 1985). Metapolygnathus was erected by Hayashi in 1968, with M. communisti as the type species, collected from cherts of the Adoyama Formation in the Ashio Mountains, central Japan.