Aduncodina unicosta Ding, 1983

Aduncodina unicosta Ding, 1983

Fig. 24R–T View Fig

*1983 Aduncodina unicosta n. sp.; Ding, p.41, pl. 6, figs. 10–14, 20(?)-21.

1983 Cornudina cf. oezdemirae Gedik ; Ding, p. 42, pl. 7, figs. 25–26

1998 Aduncodina unicosta Ding ; Koike, p. 126, fig. 8.4–8.26.

2007 Aduncodina unicosta Ding ; Orchard, p. 96, fig. 2 2019 Aduncodina unicosta Ding ; Chen et al., figs. 5.7, 5.9, 6.6.

Number of specimens. > 30.

Description. Aduncodina unicosta has been reconstructed by Koike (1998) as a quadrimembrate skeletal apparatus encompassing only Sa–c (S 1–3) and M nongeniculate coniform elements. Te adenticulated, subsymmetrical element is regarded by Koike as the M element, whereas the denticulated elements are interpreted as pertaining to the S series, the subsymmetrical one that bears one denticle being the Sa (S 0), the asymmetric one that bears up to three antero-lateral, hook-like denticles (in Zhao’s collections, those elements may bear up to five denticles, see his Ph.D thesis, 2005) and whose basal cavity is triangular in cross-section being the Sb (S 1) and the asymmetric one with a lenticular basal cavity being the Sc (S 2). All elements share common characteristics such as a thin wall, a relatively large and long and laterally flattened basal cavity. Te slender cusp is suberect and subcircular in cross-section. Basal margin weakly to strongly convex anteriorly.

Remarks. We agree with Orchard (2007) that the reconstruction by Koike (1998) might be incomplete. Neostrachanognathus was also reconstructed by Koike ( ibid) as including only coniform elements but later revised by Agematsu et al. (2008) with convincing evidence from natural assemblages as including also complex multidenticulate (bipennate) elements in the S positions. It is to be expected that Aduncodina too may possess complex multidenticulate elements in those positions. Te morphology of the illustrated elements of Aduncodina unicosta resembles that of Ordovician forms such as Strachanognathus . In common with Neostrachanognathus , Aduncodina has a suite of denticulate elements, identified as Sb and Sc by Koike (1998), with an antero-lateral denticle or process that is directed posteriorward at its base, which is a feature of the Cornudininae (Orchard, 2007).

Occurrence. Japan: Taho Formation, co-occurrence with Ic. collinsoni in the Spathian substage ( Koike, 1998); China: Biandanshan formation, co-occurrence with Ic. collinsoni and Tr. homeri, Mountain Majiashan of Chaoxian, Anhui province ( Ding, 1983). Oman: Wadi Bani Khalid section, Spathian between UA 10 and UA 11 ( Chen et al., 2019).