Scolopodus multicostatus Barnes & Tuke, 1970

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 : 212

Scolopodus multicostatus Barnes & Tuke, 1970

Fig. 26A–R

Scolopodus multicostatus Barnes & Tuke, 1970: 92 , pl. 18, figs. 5, 9, 15, 16, text-fig. 6D.

Scolopodus multicostatus .–Ethington & Clark, 1982: 101, pl. 11, figs. 19, 20.

Scolopodus multicostatus .–Stait & Druce, 1993: 310, figs. 13H–

I, 19F–J,L.

Material. 85 specimens (8 Pa, 14 Pb, 17 Sa, 17 Sb, 17 Sc, 12 Sd) from the Tabita Formation at Mount Arrowsmith, and 48 specimens (3 Pa, 7 Pb, 6 Sa, 15 Sb, 12 Sc, 5 Sd) from the unnamed dolomitic limestone unit at Koonenberry Gap .

Diagnosis. A species of Scolopodus consisting of a seximembrate apparatus including two laterally compressed scandodiform P elements with a short base, and multicostate S elements with a longer base and a broad anterior margin; symmetrical Sa and Sd elements more or less rounded in cross section, asymmetrical Sb and Sc elements laterally more compressed.

Description. P elements scandodiform with erect cusp; Pa element with a smooth outer lateral face; inner face multicostate with a median costa, an anterolateral costa, a posterior costa and a number of interposed weaker costae ( Fig. 26A,B ). Pb element has a stronger, more or less bladelike antero-inner lateral costa, and a costa along the posterior margin ( Fig. 26C–E ); outer lateral face smooth or with a few weak, short costae near the base. Sa element symmetrical, with a reclined cusp which is more or less rounded in cross section, a broad smooth anterior face, and bearing three or more costae on each posterolateral face ( Fig. 26F–I ). Sb element slightly asymmetrical, laterally compressed; cusp proclined with a broad anterior face and sharp posterior margin; the inner lateral face with two to four stronger costa and several finer ones in between; outer lateral face with a stronger anterolateral costa and several finer ones posterior to it ( Fig. 26J,K,M,N ). Sc element asymmetrical, laterally compressed; cusp suberect with a sharp posterior costa along the posterior margin and a sharp anterolateral costa on the inner side ( Fig. 26L ), as well as a number of weaker costae (typically three or four) on each lateral face; costae on the outer lateral face weaker than those on the inner lateral face ( Fig. 26 O ). Sd element nearly symmetrical, less laterally compressed in comparison with the Sb and Sc elements ; basal cavity opening rounded (often flared); broad anterior face, a costa along the posterior margin, with several costae on each of the lateral faces; the anterolateral costa on each side stronger than others ( Fig. 26Q,R ).

Remarks. Two species of Scolopodus are present in western New South Wales; S. multicostatus is distinguished in generally having fewer costae, which are also much weaker and not as sharp-edged as in the co-occurring S. quadratus . The Newfoundland type specimens of S. multicostatus figured by Barnes & Tuke (1970), which are all slightly asymmetrical with a short base and erect cusp, are identical to the New South Wales Sb elements . Stait & Druce (1993) recognized a seximembrate apparatus for S. multicostatus from the Coolibah Formation of the Georgina Basin, including scandodiform (Pa), posteriorly keeled scandodiform (Pb), acontiodiform (Sa), planoconvex (Sb), laterally compressed paltodiform (Sc) and equidimensional paltodiform (Sd) elements. The Coolibah Formation material generally exhibits more numerous, strongly developed costae than do the specimens in western New South Wales; however, Pa elements from both areas are identical. Specimens referred to the symmetrical Sa element in our collections have weakly developed costae, a broader anterior face, and a more strongly reclined cusp in comparison with the Sa element illustrated from the Coolibah Formation (Stait & Druce, 1993, fig. 19L).

Figures

Fig. 26. Scolopodus multicostatus Barnes & Tuke, 1970: A,B, Pa element, AMF120460, Y4–2, A, inner lateral view, B, outer lateral view; C,D, Pb element, AMF120461, M/A11-2, C, outer lateral view, D, postero-inner lateral view; E, Pb element, AMF120462, M/ A11-2, posterior view; F,?Sa element, AMF120463, TAB1/8.1, basal view; G–I,?Sa element, AMF120464, C1613, G,H, anterolateral views, I, anterior view; J,K, Sb element, AMF120465, C1613, J, inner lateral view, K, outer lateral view; L, Sc element, AMF120468, M/A11-1, inner lateral view; M,N, Sb element, AMF120466, C1613, M, inner lateral view, N, outer lateral view; O,P, Sc element, AMF120467, C1613, O, outer lateral view, P, inner lateral view; Q,R, Sd element,AMF120469, C1613, lateral views. Scale bars 100 µm.