Paracordylodus gracilis Lindström, 1955

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 : 13

Paracordylodus gracilis Lindström, 1955

Fig. 6A–F

Oistodus gracilis Lindström, 1955: p. 576 , pl. 5, figs 1–2.

Paracordylodus gracilis Lindström, 1955: p. 584 , pl. 6, figs 11–12; Tolmacheva & Löfgren, 2000: 1117–1119, figs 5, 7; Tolmacheva & Purnell, 2002: 209–228, text-figs 1–10; Zhen et al., 2004: p. 56, pl. 4, figs 19–22 (cum syn.).

Material. 35 specimens from sample WCB705 /243 (see Table 1) .

Remarks. Paracordylodus gracilis is one of the best known species in the Early Ordovician. The reconstructed apparatus initially was based on interpretation of collections of discrete specimens documented successively by Sweet & Bergström (1972), McTavish (1973), and van Wamel (1974). Their collective interpretations were confirmed nearly 30 years later by the in situ bedding plane assemblages (Tolmacheva & Löfgren, 2000; Tolmacheva & Purnell, 2002). Its species composition and structure based on numerous clusters from deep water radiolarian cherts in central Kazakhstan revealed important data about its evolutionary affinities (Tolmacheva & Purnell, 2002). Paracordylodus gracilis is widely distributed (see Tolmacheva & Löfgren, 2000; Tolmacheva & Purnell, 2002), ranging from the late Tremadocian (late P. proteus Biozone ) to late Floian (mid O. evae Biozone ). It was most common in the Open Sea Realm (from shelf edge to basinal setting), with typical examples reported in central Kazakhstan (Tolmacheva & Purnell, 2002) occurring as the dominant species making up 90–99% of the specimen numbers. It is present in similar deep water oceanic settings in cherts of turbiditic successions ( Percival et al., 2003), and also in allochthonous limestone or calcareous siltstone of slope settings ( Zhen et al., 2004) in eastern Australia on the margins of eastern Gondwana. Paracordylodus gracilis was also common in the shallow marine environments within the Cold Domain of the Shallow-Sea Realm, such as in the Balto- Scandian Province ( Löfgren, 1978; Tolmacheva & Löfgren, 2000). Its occasional presence in outer shelf environments or more rarely in inner shelf habitats within Temperate or even Tropical domains can be attributed to up-welling of cold ocean currents.

Figures

Fig. 6. A–F, Paracordylodus gracilis Lindström, 1955. All from sample WCB705/243. (A), M element, CPC39827, anterior view (IY116-050). B–E, S elements; B–C, CPC39828, (B), inner lateral view (IY116-051); (C), close up showing chevron-shaped pattern of striae adjacent to anterior margin (IY126-052); (D), CPC39829, inner lateral view (IY126-053); (E), CPC39830, outer lateral view (IY126-054); (F), P element, CPC39928, outer lateral view (IY116055). G,H,L, Prioniodus adami Stouge & Bagnoli, 1988. G,H, Pa element, CPC39831, WCB705/243, (G), antero-outer lateral view (IY118-018); (H), outer lateral view (IY118-019). (L), Sa element, CPC39832, WCB705/243, posterior view (IY128-021). M–R, Protoprioniodus simplicissimus McTavish, 1973. All from sample WCB705/243. M, N, Sc element; (M), CPC39833, outer lateral view (IY118-020); (N), CPC39834, inner lateral view (IY118-030). O,P, Pa element, CPC39835, (O), inner lateral view (IY118-025); (P), upper-outer lateral view (IY118-023). Q,R, M element; (Q), CPC39836, anterior view (IY129-032); (R), CPC39837, posterior view (IY118-029). I–K, S–V, Fahraeusodus adentatus (McTavish, 1973). I–K, Sa element, CPC39838, WCB705/133, (I), lateral view (IY127-012); (J), anterior view, close up showing striae on the broad anterior face (IY127-011); (K), anterior view (IY127-010). (S), Sc element, CPC39839, 161–166 m, inner lateral view (IY130-001). (T), Sb element, CPC39840, 161–166 m, outer lateral view (IY130-002). U,V, Sd element, CPC39841, 161–166 m, (U), inner lateral view (IY130-005); (V), outer lateral view (IY130-006). Scale bars 100 µm unless otherwise indicated.