Polonodus Dzik, 1976

Zhen, Yong Yi, 2011, Middle to Late Ordovician (Darriwilian-Sandbian) Conodonts from the Dawangou Section, Kalpin Area of the Tarim Basin, Northwestern China, Records of the Australian Museum 63 (3), pp. 203-266 : 232-233

Polonodus Dzik, 1976

Type species. Ambalodus clivosus Viira, 1974 .

Remarks. Based on the pectiniform elements of the monotypic species, Ambalodus clivosus Viira, 1974 , Dzik (1976, p. 423) provided a brief diagnosis for Polonodus as “conical conodonts with four lobes covered with concentric and radial rows of tubercles” having a “very large basal cavity”, and illustrated three specimens showing a wide range of morphology including four-lobed ( Dzik, 1976, fig. 29c), three-lobed ( Dzik, 1976, pl. 43, fig. 1a–b), and an incomplete specimen with a well-developed anterior platform ( Dzik, 1976, fig. 29d). By applying a form species approach, Löfgren (1978) suggested that the Polish specimens illustrated by Dzik (1976) were not conspecific with the holotype of P. clivosus , and in fact they represented two species that were doubtfully included in Polonodus as P.? sp. A (= Dzik, 1976, pl. 43, fig. 1a–b) and P.? sp. B (= Dzik, 1976, fig. 29c–d). Stouge (1984) revised the type species, P. clivosus , and also named two new species ( Polonodus tablepointensis and P.? newfoundlandensis ) from the Table Head Formation of western Newfoundland. In the synonymy list of bimembrate P. tablepointensis he included specimens illustrated by Dzik (1976, fig. 28c–d) as P. clivosus and those ascribed to P.? sp. A and P.? sp. B by Löfgren (1978). Stouge (1984) then divided three species occurring in the Table Head Formation into two groups. His first group included P. clivosus and P. newfoundlandensis , with P. tablepointensis comprising the second group. Zhang (1998c) erected Dzikodus with P. tablepointensis as the type species, and also included M and S elements in the species apparatus of the latter.

Stouge (1984) only doubtfully considered his first group ( P. clivosus and P. newfoundlandensis ) as Polonodus , preferring to accept a generic definition based on Dzik’s (1976) material from Polish erratic boulders rather than the type material of Ambalodus clivosus Viira, 1974 . However, Löfgren (1990) argued that P. clivosus (Viira) might be more closely related to P. tablepointensis rather than P. newfoundlandensis as Stouge (1984) suggested.

Stouge (1984) recognized two paired pectiniform elements (polyplacognathiform and ambalodiform) in Polonodus . Löfgren (1990) recognized geniculate M and ramiform S (including trichnodelliform = Sa, gothodiform = Sb, and tetraprioniodiform = Sd) elements in the species apparatus of Polonodus . It is likely that the species apparatus might also include a modified bipennate ramiform element similar to that illustrated by Löfgren (1990, fig. 1e) to take the Sc position.