Oepikodus pincallyensis Zhen

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 : 201-203

Oepikodus pincallyensis Zhen n.sp.

Figs. 19A–N , 20A–R

Etymology. After Pincally Homestead ( Fig. 1 ), which is located southwest of the type locality (Y4).

Material. Three specimens (1 M, 1 Sa, 1 Sc) from limestone nodules within shales of the upper Yandaminta Quartzite, and 92 specimens (13 Pa, 11 Pb, 16 M, 16 Sa, 10 Sc, 17 Sb, 9 Sd) from the overlying Tabita Formation at Mount Arrowsmith , western New South Wales, including the HOLOTYPE AMF120398 (Pb element), from sample Y4–2 (C1822), and 15 paratypes AMF120399–120402, AMF120404–120411, AMF124210–124212.

Diagnosis. A species of Oepikodus consisting of a septimembrate apparatus with a ramiform-pectiniform structure; all elements albid; both Pa and Pb elements pastinate with a longer denticulate posterior process, a shorter denticulate outer lateral process, and an innerlaterally curved anterior process which is adenticulate (Pa) or denticulate (Pb); S elements typical (Sa and Sd) or modified (Sb and Sc) quadriramate.

Description. Pa element has a prominent, slightly procline, laterally compressed cusp which is triangular in cross section, with sharp posterior and anterior margins; an inwardly curved blade-like costa extends along the anterior margin, merging downward into the upper margin of an adenticulate, inwardly curved, anterior process ( Fig. 19E ); outer lateral face has a rounded distinctive costa that extends downwards to merge into the upper margin of the outer lateral process ( Fig. 19B ); the outer lateral process extends anterolaterally forming an obtuse angle with the posterior process ( Fig. 19E ); small, closely spaced denticles developed on the posterior and outer lateral processes ( Fig. 19B–E ); in upper view, these processes meet at a Y-shaped junction; basal cavity triangular in outline ( Fig. 19F ); none of the specimens recovered have processes preserved for their full length. Pb element similar to the Pa, with denticulate outer lateral and posterior processes, but with the cusp more or less erect or slightly reclined, also with a blade-like anterior costa that extends basally to merge into a shorter, denticulate, anterior process ( Fig. 19G–L ); outer lateral process extending more or less normal to the posterior process ( Fig. 19K ). M element geniculate, makellate, with a long adenticulate outer lateral process and a shorter, triangular adenticulate inner lateral process (anticusp) ( Fig. 19A,M,N ); cusp robust, inclined outer laterally, and also slightly curved posteriorly, anteroposteriorly compressed with sharp lateral margins, and a strong rounded costa on the anterior and posterior faces; surface ornament of fine striae; anterior costa extending to the basal margin, becoming stronger and wider on the base; posterior costa extending into a moderately developed basal buttress; outer lateral process with a sharp, gently arched upper margin and costa extending from cusp to distal end of the process on each of its sides, and more or less parallel to the basal margin; inner lateral process with a sharp upper margin which is a continuously straight extension of the inner lateral margin of the cusp; basal cavity shallow, extending as narrow grooves underneath the lateral processes, with only slightly arched basal margin. Sa element symmetrical or nearly so, and quadriramate; cusp slightly proclined, more or less diamond-shaped in cross section with sharp anterior and posterior margins and a sharp costa on each lateral side; anterior margin extended basally into a long downwardly directed anticusp; sharp lateral process extending basally into a weakly developed rudimentary adenticulate lateral process on each side; posterior process long, denticulate, bearing closely spaced and erect denticles of different sizes, larger denticles about two or three times as wide as the smaller denticles in the lateral view, typically with three to five smaller denticles between two larger denticles; basal margin of the posterior process nearly straight, forming an angle of about 40 to 50° with the basal margin of the anticusp ( Fig. 20A–D). Sb element asymmetrical, with a weak carina on the inner lateral face, an inner laterally curved posterior process, and a proclined cusp; on the outer lateral face a prominent costa is developed which extends basally into a short adenticulate outer lateral process ( Fig. 20I–M). Sc element similar to Sb, modified quadriramate, asymmetrical with cusp and anticusp slightly curved inwards; cusp erect or slightly proclined with sharp anterior and posterior margins, smooth outer lateral face and a weak carina on the inner lateral face; posterior process long, extending posteriorly as well as downwards, with a slightly arched upper margin, bearing numerous small, laterally compressed, and closely spaced denticles; none of the specimens examined have the full length of the posterior process preserved; anticusp long, triangular in shape, extending anteriorly and downwards, forming an angle of about 70–80° with the posterior process ( Fig. 20E–H). Sd element quadriramate, like the Sa but asymmetrical, with cusp and the anterior process (anticusp) prominently curved inward, and with a long denticulated posterior process, a sharp anterior margin extended basally into a strongly downwardly directed anticusp; cusp proclined, more or less diamond-shaped in cross section, with sharp posterior and anterior margins, and a strong costa on each lateral face, which extends basally into a rudimentary adenticulate lateral process on each side ( Fig. 20N–R).

Remarks. S and M elements of O. evae , O. communis and the new species O. pincallyensis closely resemble each other. Oepikodus evae was revised recently in detail (Stewart & Nicoll, in press) based on material from Australia and Sweden including well preserved bedding-plane assemblages. Compared with the revised concept of O. evae , the new species has a short anticusp in the M and S elements , and the Sb and Sc elements exhibit only rudimentary development of the lateral processes, which are reduced to a weakly developed carina on the inner lateral face of the Sb and Sc elements . Denticles on the posterior process in the S elements of O. communis are regular in size, whereas Sa elements of O. pincallyensis display variably sized denticles. Instead of a rather arched basal margin in the M elements of both O. evae and O. communis , O. pincallyensis shows a more or less straight basal margin. However, differentiation of these three species is mainly reliant on the P elements , specifically the absence of denticles on both the anterior and outer lateral processes on the P element of O. communis . The new species differs from O. evae in having smaller, rudimentary denticles on the anterior and outer lateral processes of the P elements . Furthermore, the anterior and outer lateral processes in the P element of O. evae , as shown by the type material from the Lower Ordovician of south-central Sweden ( Lindström, 1955) and newly documented specimens from Australia (Stewart & Nicoll, in press), extend strongly downwards. In possessing smaller denticles and much less downwardly extended anterior and outer lateral processes on the P elements , the new species more closely resembles Oepikodus communis (Ethington & Clark, 1964) , and Oepikodus intermedius Serpagli, 1974 , but both of these latter species (which are probably conspecific) have adenticulate anterior and outer lateral processes.

In a recent study of the conodonts from the Horn Valley Siltstone of central Australia, Nicoll & Ethington (in press) recognized another new species of Oepikodus , previously recorded by Cooper (1981) as O. evae . It differs from O. pincallyensis and other Oepikodus species in having a pronounced v-shaped cleft separating the posterior margin of the cusp and the first denticle of the posterior process in the S and P elements . Rudimentary denticles are also developed on the anterior process of some Sc, Sb and M elements of this species from Horn Valley Siltstone.

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.

Fig. 1. Localities and geological maps of the studied areas. Maps of Australia and New South Wales, showing location of Mount Arrowsmith (B) and Koonenberry Range (C) areas to the north of Broken Hill. B, geological map of the Mount Arrowsmith area (modified after unpublished mapping by B. Stevens and K.J. Mills, Geological Survey of NSW Broken Hill office), showing locations of conodont samples collected from the Yandaminta Quartzite and Tabita Formation, Australian Map Grid coordinates from Mount Arrowsmith 7237 orthophotomap (first edition, 1978). C, map of the Koonenberry Gap area showing locations of samples collected for conodonts, Australian Map Grid coordinates from Wonnaminta 7336 orthophotomap (first edition, 1978).