Scalpellodus latus ( van Wamel, 1974 )

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 : 211

Scalpellodus latus ( van Wamel, 1974)

Fig. 25A–J

Protopanderodus latus van Wamel, 1974: 91 , pl. 4, figs. 1–3.

Scalpellodus latus .– Löfgren, 1978: 99, pl. 5, figs. 10, 14, pl. 6, figs. 1–4, 7, 21 (cum syn.).

Scalpellodus latus .– Cooper, 1981: 179, pl. 27, figs. 7–10, 13–15.

Material. One specimen (Sa) from limestone nodules within shales of the upper Yandaminta Quartzite and 28 specimens (1 P?, 2 Sa, 12 Sb, 5 Sc, 6 Sd) from the overlying Tabita Formation at Mount Arrowsmith .

Remarks. This coniform species is similar to Cornuodus longibasis , but is more laterally compressed, and ornamented with fine striae ( Fig. 25A,H ), which is a critical character in recognition of this species. Of the three morphotypes distinguished by Cooper (1981), we also recognize a symmetrical Sa element with a broad anterior face, a sharp costa on each lateral face, and a costa along the posterior margin ( Fig. 25A,B ). All three costae on the Mount Arrowsmith specimens are relatively weakly developed in comparison with the Sa element illustrated from the Horn Valley Siltstone ( Cooper, 1981, pl. 27, figs. 7, 9). Asymmetrical forms (defined as the Sb element by Cooper), with a sharp posterior margin and an anterolateral costa only on the inner lateral side, can be segregated into an Sb element ( Fig. 25C,D ) with a proclined cusp, and another type with an erect cusp and a more laterally compressed base—here referred to the Sd element ( Fig.

25E,F,H,I). The nearly symmetrical element with sharp anterior and posterior margins, which Cooper (1981) identified as the Sc element , is also recognized ( Fig. 25J ). A small, nearly symmetrical specimen with a recurved cusp ( Fig. 25G ) possibly occupied the P position of this species.

Figures

Fig. 25. Scalpellodus latus (van Wamel, 1974): A,B, Sa element, AMF120452, Y4–2, A, inner lateral view of the basal part showing the fine striae, B, lateral view; C, Sb element, AMF120453, Y4–2, inner lateral view; D, Sb element, AMF120454, M/A11-1, inner lateral view; E,H, Sd element, AMF120455, M/A7, E, inner lateral view, H, close up showing fine striae; F, Sd element, AMF120456, M/A7, posterior view; G, P element, AMF120457, TAB1/39.5, inner lateral view; I, Sd element, AMF120458, M/A7, inner lateral view; J, Sc element, AMF120459, Y4–2, lateral view. Scale bars 100 µm, unless otherwise indicated.