Semiacontiodus sp.

Zhen, Yong Yi & Nicoll, Robert S., 2009, Biogeographic and Biostratigraphic Implications of the Serratognathus bilobatus Fauna (Conodonta) from the Emanuel Formation (Early Ordovician) of the Canning Basin, Western Australia, Records of the Australian Museum 61 (1), pp. 1-30 : 22

Semiacontiodus sp. cf. Semiacontiodus cornuformis ( Sergeeva, 1963)

Fig. 15L–T

Scolopodus cornuformis Sergeeva. — An, 1987: 183, pl. 7, figs 10–11, 13–16; Ding et al. in Wang, 1993: 202, pl. 5, fig. 33; Zhen et al., in press a: fig. 9D–F.

Material. 26 specimens from three samples ( Table1).

Remarks. Three morphotypes of this species are recognized in the Emanuel samples representing a symmetry transition series including symmetrical Sa ( Fig. 15L,M ), asymmetrical Sb ( Fig. 15N,O ), and strongly asymmetrical and laterally more compressed Sc ( Fig. 15P–T ) elements.Although these specimens have relatively shorter bases, they otherwise resemble those of S. cornuformis ( Sergeeva, 1963) , which was revised as consisting of a septimembrate apparatus ( Löfgren, 1999).

Figures

Fig. 15. A–H, Stiptognathus borealis (Repetski, 1982). (A), M element, CPC39902, WCB705/243, posterior view (IY129-033). B–D, Sa element; B,C, CPC39903, WCB705/243, (B), upper-posterior view (IY118-006), (C), upper-anterior view (IY118-007); (D), CPC39904, WCB705/243, upper view showing the cross section of the cusp (IY118-004). E–G, Sb element, E,G, CPC39905, WCB705/133, (E), basal-posterior view (IY117-041), (G), posterior view (IY117-039). (F), CPC39906, WCB705/243, basal view (IY118-015). (H), Pb element, CPC39907,WCB705/243, antero-inner lateral view (IY118-008).I–K, Triangulodus bifidus Zhen inZhen et al., 2006.Sd element, CPC39908, WCB705/133, (I), basal view (IY116-056), (J,K), posterolateral views (IY116-058, IY116-057). L–T, Semiacontiodus sp. cf. S. cornuformis (Sergeeva, 1963). L,M, Sa element, CPC39909, WCB705/133, (L), posterior view (IY126-027); (M), posterolateral view (IY126-028). N,O, Sb element; (N), CPC39910, 161–166 m, inner lateral view (IY132-012); (O), CPC39911, 161–166 m, outer lateral view (IY132-014). P–T, Sc element; P–R, CPC39912, 161–166 m, (P), inner lateral view (IY132-016); (Q), basal view (IY132-018); (R), outer lateral view (IY132-017). S,T, CPC39913, WCB705/133, (S), inner lateral view (IY127-018); (T), close up showing fine striae (IY127-019). Scale bars 100 µm unless otherwise indicated.