Drepanoistodus basiovalis ( Sergeeva, 1963 )

Zhen, Yong Yi, Percival, Ian G. & Webby, Barry D., 2003, Early Ordovician Conodonts from Far Western New South Wales, Australia, Records of the Australian Museum 55 (2), pp. 169-220 : 191

Drepanoistodus basiovalis ( Sergeeva, 1963)

Fig. 14A–K

Oistodus basiovalis Sergeeva, 1963: 96 , pl. 7, figs. 6, 7, text-fig. 3.

Drepanoistodus basiovalis Löfgren, 1978: 55 , pl. 1, figs. 11–17, fig. 26B,C (cum syn.).

Drepanoistodus suberectus Cooper, 1981: 164 , pl. 26, figs. 1, 2, 6.

Drepanoistodus basiovalis .–Johnston & Barnes, 2000: 18, pl. 11, figs. 10, 11, 15, 16 (cum syn.).

Material. Thirteen specimens (4 P, 1 M, 1 Sa, 3 Sb, 4 Sc) from limestone nodules within shales of the upper Yandaminta Quartzite, and 123 specimens (11 P, 31 M, 21 Sa, 41 Sb, 19 Sc) from the overlying Tabita Formation at Mount Arrowsmith ; 21 specimens (3 P, 4 Sa, 8 Sb, 6 Sc) from unnamed dolomitic limestone unit at Koonenberry Gap .

Description. Apparatus quinquimembrate, all elements are hyaline, laterally compressed with sharp anterior and posterior margins, non-costate lateral faces, and have an open basal cavity. The P element ( Fig. 14A,B,D–F,H ) is asymmetrical with a reclined cusp and an extended anterobasal corner, triangular in outline. The M element is geniculate with a short outer lateral process, and a rounded inner lateral corner; a mid-carina may develop on the anterior and posterior faces ( Fig. 14J,K ). The S elements consist of a symmetrical (or nearly so) Sa element with an erect cusp ( Fig. 14G ), an asymmetrical Sb element with a reclined cusp and an oval-shaped opening of the basal cavity ( Fig. 14C ), and an asymmetrical Sc element with a strongly recurved, more laterally compressed cusp, having a narrower opening of the basal cavity ( Fig. 14I ).

Remarks. The definition of this widely distributed species given by Löfgren (1978) is followed here. However, the element with an outer lateral costa ( Löfgren, 1978, pl. 1, fig. 12) is not recognized in our collections. The P element corresponds to the scandodiform element of many previous authors (e.g., Stouge & Bagnoli, 1990, pl. 5, fig. 19). Compared with their material from Sweden, M elements from western New South Wales are characterized by a shorter outer lateral process.

Figures

Fig. 14. A–K, Drepanoistodus basiovalis (Sergeeva, 1963): A,B, P element, AMF120351, Y4–2, A, outer lateral view, B, basal view; C, Sb element,AMF120352, M/A7, outer lateral view; D–F, P element,AMF120354,W5, D, outer lateral view, E, posterior view, F, inner lateral view; G, Sa element, AMF120356, M/A11-3, lateral view; H, P element, AMF120355, Y4–2, outer lateral view; I, Sc element, AMF120358, M/A11-2, inner lateral view; J, M element, AMF120357, Y4–2, anterior view; K, M element, AMF120353, A/M11–3, posterior view. L, Drepanoistodus sp., AMF120360, W5, outer lateral view. M–O, Ulrichodina sp. cf. simplex Ethington & Clark, 1982, AMF120359, W5, M,N, lateral views, O, basal view. Scale bars 100 µm.