Oepikodus communis (Ethington & Clark, 1964)

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 : 199-201

Oepikodus communis (Ethington & Clark, 1964)

Fig. 19 O

Gothodus communis Ethington & Clark, 1964: 690–692 , pl. 114, figs. 6, 14, text-fig. 2F.

Oepikodus equidentatus Ethington & Clark, 1964: 692–693 , pl. 113, figs. 6, 8, 10, 11, 14.

Subcordylodus sp. aff. S. delicatus (Branson & Mehl) Ethington & Clark, 1964: 701–702 , pl. 115, figs. 1, 5, 7, 10.

Oepikodus communis .–Ethington & Clark, 1982: 61–62, pl. 6, figs. 18, 22, 25 (cum syn.).

Oepikodus communis .– Smith, 1991: 42, figs. 24a–f,i,j, 25, 26 (cum syn.).

Material. One Pb element, from the Tabita Formation, at Mount Arrowsmith.

Remarks. Oepikodus communis is extremely rare at Mount Arrowsmith; the single Pb element recovered (sample M/ A11-2) has a denticulate posterior process, and adenticulate outer lateral and anterior processes ( Fig. 19O ). Morphological differentiation and apparatus composition of O. evae , O. communis and O. intermedius have been widely discussed in Ordovician conodont literature. Serpagli (1974) considered O. intermedius to be transitional between O. evae and O. communis , showing O. intermedius first appearing in the San Juan Formation directly above the last appearance of O. evae . He further correlated the range of O. intermedius in the San Juan Formation with the O. communis Zone of the North American Midcontinent faunal succession, and suggested an evolutionary trend from O. evae – O.

intermedius– O. communis . More recently, however, the O. communis Zone has been correlated in part with the P. elegans Zone , below the O. evae Zone ( Webby, 1995) , implying that O. intermedius might be the youngest species of the three. Although Serpagli (1974) distinguished O. intermedius from O. communis on curvature of processes on the P elements and curvature of the basal margin of the M elements , we agree with most subsequent authors (Ethington & Clark, 1982; Repetski, 1982; Smith, 1991) that these details are within the variation of O. communis . However, merging of these two species has the effect of extending the range of O. communis upwards into the flabellum /laevis Zone.

Figures

Fig. 19. A–N, Oepikodus pincallyensis Zhen sp. nov.: A, M element, paratype, AMF120399, M/A7, anterior view; B,C, Pa element, paratype, AMF120401, Y4–2, B, outer lateral view, C, anterior view; D,E, Pa element, paratype, AMF120402, Y4–2, D, outer lateral view, E, upper view; F, Pa element, paratype,AMF124210, M/A7, basal view; G,H, paratype, Pb element,AMF124211, Y4–2, G, outer lateral view, H, anterior view; I–L, Pb element, Holotype, AMF120398, Y4–2, I, antero-outer lateral view, J, inner lateral view, K, upper view, L, outer lateral view; M,N, M element, paratype, AMF120400, M/A/7, M, posterior view, N, postero-inner lateral view, showing basal buttress. O, Oepikodus communis (Ethington & Clark, 1964): Pb element,AMF120403, M/A11-2, outer lateral view. Scale bars 100 µm.