Drepanodus sp.

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 : 190

Drepanodus sp.

Fig. 13E–I

Material. Eight specimens (2 arcuatiform, 2 graciliform, 4 sculponeaform) from limestone nodules within shales of the upper Yandaminta Quartzite, and 52 specimens (23 arcuatiform, 17 graciliform, 12 sculponeaform) from the overlying Tabita Formation at Mount Arrowsmith ; ten specimens (5 arcuatiform, 3 graciliform, 2 sculponeaform) from unnamed dolomitic limestone unit at Koonenberry Gap .

Remarks. This species of Drepanodus comprises small, albid, laterally compressed, conical units with sharp anterior and posterior margins and smooth lateral sides. The basal cavity is relatively deep, extending to near the maximum curvature of the cusp. Three morphotypes have been recovered. The arcuatiform element is nearly symmetrical with a proclined cusp. The graciliform element is asymmetrical with a slightly reclined cusp, and the sculponeaform element is nearly symmetrical and has a recurved cusp. Elements resemble those of the type species of the genus, but lack a prominent mid-carina on the lateral faces ( van Wamel, 1974). Arcuatiform elements referred to D. arcuatus , illustrated from the Ninguo Formation of southeast China (Z.H. Wang & Bergström, 1999, pl. 2, figs. 4, 5), also have smooth lateral faces, but the Chinese specimens exhibit a posteriorly reclined cusp.

Drepanoistodus Lindström, 1971

Type species. Oistodus forceps Lindström, 1955 .

Remarks. Nicoll (1994) suggested that most euconodonts in the Order Protopanderodontida comprised seximembrate coniform-coniform apparatuses including S (Sa, Sb, Sc, Sd) and P (Pa, Pb) elements. However, this configuration for coniform species has not subsequently been widely accepted. Hence the commonly used notation schemes are followed for the two species of Drepanoistodus documented herein.

Figures

Fig. 13. A–D, Cornuodus longibasis (Lindström, 1955): A, Sa element, AMF120342, Y4–2, lateral view; B, Sa element, AMF120343, M/A11-3, lateral view; C, Sd2 element, AMF120344, M/A11-3, lateral view; D, Sb element, AMF120345, M/A11-2, inner lateral view. E–I, Drepanodus sp.: E, sculponeaform element,AMF120346, C1613, outer lateral view; F, sculponeaform element,AMF120347, W5, inner lateral view; G. arcuatiform element,AMF120348, C1612, inner lateral view; H, arcuatiform element, AMF120349, C1613, outer lateral view; I, graciliform element, AMF120350, Y4–8, outer lateral view. Scale bars 100 µm.