Eurygnathodus hamadai ( Koike, 1982 )

Leu, Marc, Bucher, Hugo, Vennemann, Torsten, Bagherpour, Borhan, Ji, Cheng, Brosse, Morgane & Goudemand, Nicolas, 2022, A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China, Swiss Journal of Palaeontology (19) 141 (1), pp. 1-61 : 53

publication ID	https://doi.org/ 10.1186/s13358-022-00259-x
persistent identifier	https://treatment.plazi.org/id/038B1D1D-645D-FF85-FF1B-EDFBD0EBFA07
treatment provided by	Felipe
scientific name	Eurygnathodus hamadai ( Koike, 1982 )
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Eurygnathodus hamadai ( Koike, 1982)

Fig. 14B View Fig

1981 Platyvillosus costatus (Staesche) ; Wang and Cao, p. 371, pl. 2, figs. 31–32.

*1982 Platyvillosus hamadai n. sp.; Koike, p.45, pl. 5, figs. 10–36.

1988 Platyvillosus hamadai Koike ; Koike, p. 71, pl. 2, figs. 38–45.

2010 Eurygnathodus hamadai (Koike) ; Orchard, p. 145, fig. 5.11.

2015 Eurygnathodus hamadai (Koike) ; Maekawa in Maekawa et al., p. 317, fig. 5.2.

2018 Eurygnathodus hamadai (Koike) ; Maekawa in Maekawa et al., p. 50, figs. 28.1–28.4.

2019 Eurygnathodus hamadai (Koike) ; Li et al., p. 6, figs. 4.37–4.45.

2019a Eurygnathodus hamadai (Koike) ; Wu et al., fig. 4.22.

Material.> 30 specimens.

Remarks. Eurygnathodus hamadai is easily distinguished from Eurygnathodus costatus by its smooth, flat upper surface lacking ornamentation. Koike (1988) reported transitional forms between E. costatus and E. hamadai (Morphotype δ), raising the question whether both forms may be conspecific, E. hamadai representing an extreme variant of E. costatus . In our material and in that of other authors, Eu. costatus and Eu hamadai co-occur in several samples. Teir relative abundance, however, does change. Eu. costatus is more common in older strata, whereas Eu. hamadai is more abundant than Eu. costatus in younger strata. Although the FO of Eu. costatus appears to predate that of Eu. hamadai in several sections around the world, it is thus still unclear whether they share the same temporal range or not.

Occurrence. early Smithian in China ( Wang & Cao, 1981, this study), Malaysia ( Koike, 1982), Japan ( Koike, 1988; Maekawa et al., 2018, and India, Spiti ( Orchard, 2010).