Aduncodina unicosta Ding, 1983

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 : 51-52

Aduncodina unicosta Ding, 1983

Fig. 24R–T

*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).

Figures

Fig.24 Novispathodinae and uncertain from Qiakong,Laren,Shanggang,and Lilong. Magnification is×80.The scale bar is 400 μm.All elements are considered to be P1 elements if not specifically identified otherwise.A, D, G, H Triassospathodushomeri (Bender);A LIL515C,PIMUZ 39313;D QIA155,PIMUZ 39314;G LIL513B,PIMUZ 39315;H LIL515B,PIMUZ 39316.B, E, F Triassospathodus aff.symmetricus (Orchard);B QIA138,PIMUZ 39306;E LIL505,PIMUZ 39307; F QIA136,PIMUZ 39308.C, I–Q Triassospathodussymmetricus (Orchard);C QIA140,PIMUZ 39326;I SHA313,PIMUZ 39327;J QIA143,PIMUZ 39328;K QIA144, PIMUZ 39329;L QIA141,PIMUZ 39330;M LIL515D,PIMUZ 39331;N LIL509,PIMUZ 39332;O LIL513B,PIMUZ 39333;P LIL513B,PIMUZ 39334;Q LIL513A, PIMUZ 39335.R–T Aduncodina unicosta (Ding);R BAN5,PIMUZ 39100;S SHA320,PIMUZ 39101;T SHA318,PIMUZ 39102