Tropodus australis ( Serpagli, 1974 )

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 : 27

Tropodus australis ( Serpagli, 1974)

Fig. 16A–P

Walliserodus australis Serpagli, 1974: 89–91 , pl. 19, figs 5a–10c, pl. 29, figs 8–15, text-figs 23, 24.

Tropodus australis (Serpagli) .— Albanesi et al., 1998: 151, pl. 13, figs 12–18.

Tropodus comptus australis (Serpagli) .— Stouge & Bagnoli, 1988: 141, 142, pl. 16, figs 3–5; Löfgren, 1993: fig. 9: o, s, t; Lehnert, 1993: pl. 4, fig. 5; Lehnert, 1995: 129, 130.

Acodus comptus (Branson & Mehl, 1933) .— Zhen et al., 2004: 50, 51, pl. 1, figs 1–19.

Scolopodus ? rex Lindström. — Percival et al., 1999: 13, fig. 8.9.

Tropodus ? sweeti (Serpagli) .— Percival et al., 1999: 13, fig. 8.10.

Material. 190 specimens from three samples ( Table 1).

Remarks. Specimens from the Emanuel Formation are identical with those recovered from the Hensleigh Siltstone of central New South Wales ( Zhen et al., 2004, pl. 1, figs 1–19). Stouge & Bagnoli (1988) regarded W. australis as a subspecies of T. comptus . In the Emanuel Formation samples, only one species of Tropodus , T. australis is represented, exhibiting similar variation of the S elements ( Fig. 16C–K ) as was documented by Serpagli (1974), and the P elements ( Fig. 16L–P ) that are comparable with those described by Stouge & Bagnoli (1988) from the Cow Head Group of Newfoundland.

Tropodus australis differs from typical T. comptus of the North American Mid-continent ( Kennedy, 1980; Ethington & Clark, 1982; Landing & Wesrop, 2006) mainly in having a strongly laterally compressed, muti-costate (Sc) element. Landing & Westrop (2006) documented T. comptus from the Fort Cassin (Early Ordovician, Floian) of northeastern New York, and defined it as consisting of a septimembrate apparatus including S, M and P elements, and also illustrated a scandodiform element as representing the Sc position (see Landing & Westrop, 2006, fig. 6.15). In the study of conodont faunas from the Jefferson City and other equivalent units in Oklahoma (Kindblade), Ethington (2009, per. com.) recognized the possible P elements of T. comptus and noticed their considerable difference from those of T. australis illustrated herein from the Emanuel Formation. He suggested that elements of T. australis tended to be heavier whereas those of T. comptus were more subdued.

ACKNOWLEDGMENTS. Study by YYZ was partially supported by the CAS/SAFEA International Partnership Program for Creative Research Teams. Scanning electron microscope photographs were prepared in the Electron Microscope Unit of the Australian Museum. Dr Ian Percival is thanked for carefully reading and helping with linguistic expression on an early version of the manuscript. G.S Nowlan, R.L. Ethington and S.A. Leslie are thanked for their careful and constructive reviews of the manuscript. This is a contribution to IGCP Project 503: Ordovician Palaeogeography and Palaeoclimate.

Figures

Fig.16. Tropodus australis (Serpagli, 1974). A,B, M element; (A), CPC39914, WCB705/243, posterior view (IY128-032); (B), CPC39915, WCB705/243, anterior view (IY129-007).(C), Sa element, CPC39916, WCB705/243, posterior view (IY128-034).(D), Sb1 element (tricostate), CPC39917, WCB705/243, outer lateral view (IY128-033). E,F, Sb2 element (four costate); (E), CPC39918,WCB705/243, outer lateral view (IY128-038); (F), CPC39919,WCB705/243, inner lateral view (IY128-036).G–I, Sc element; (G), CPC39920,WCB705/243, outer lateral view (IY129-003); (H), CPC39921, WCB705/243, inner lateral view (IY129-022); (I), CPC39922, WCB705/243, inner lateral view (IY118-032). J,K, Sd element, CPC39923, WCB705/243, (J), basal view (IY118-033), (K), basal view close up showing the lamellar structure in the basal cavity (IY118-034). L–N, Pa element; (L), CPC39924, WCB705/243, outer lateral view (IY128-028); (M), CPC39925, WCB705/243, inner lateral view (IY128-022); (N), CPC39926, WCB705/243, inner lateral view (IY128-029). O,P, Pb element, CPC39927, WCB705/243; (O), outer lateral view (IY129-031), (P), basal view (IY129-030). Scale bars 100 µm.