Histiodella kristinae Stouge, 1984

Zhen, Yong Yi, 2011, Middle to Late Ordovician (Darriwilian-Sandbian) Conodonts from the Dawangou Section, Kalpin Area of the Tarim Basin, Northwestern China, Records of the Australian Museum 63 (3), pp. 203-266 : 229

Histiodella kristinae Stouge, 1984

Fig. 14C–F

Histiodella kristinae Stouge, 1984: 87 , pl. 18, figs 1–7, 9–11, fig. 17 (cum syn.); Dzik, 1994: 110, pl. 24, figs 28–30, text-fig. 30; Wang & Zhou, 1998: pl. 3, fig. 5; Zhang, 1998c: 72–73, pl. 9, figs 16–17 (cum syn.); Zhao et al., 2000: 206, pl. 27, fig. 11; Rasmussen, 2001: 84, pl. 8, figs1–3, 5; Löfgren, 2004: fig. 7u; Du et al., 2005: 365, pl. 1, figs 6–21; Chen et al., 2006: fig. 10X–Y; Viira, 2011: fig. 9N–O.

Histiodella holodentata Ethington & Clark. –Nowlan & Thurlow, 1984: pl. 1, figs 1, 3, 5; Wang et al., 1996: pl. 1, figs 12–13; Rasmussen, 2001: 82, partim only pl. 7, fig. 19; Löfgren, 2004: fig. 7t.

Histiodella intertexta An in An et al., 1981: pl. 1, fig. 20 (nomen nudum); Ding et al. in Wang, 1993: 181, pl. 29, fig. 11.

Histiodella serrata Harris. – Landing, 1976: 633–634, pl. 1, fig. 20; Wang & Lou, 1984: 262–263, pl. 10, fig. 1, pl. 11, figs 6–7.

Histiodella sp. nov. 1 Ni, 1981: pl. 1, fig. 26.

Material. 30 specimens from one sample at the top of the Dawangou Formation ( Table 2).

Remarks. Histiodella species are morphologically distinctive, and several including H. kristinae , H. holodentata and others have been widely used as index fossils in the Middle Ordovician of the North American Mid-Continent, Argentine Precordillera, South China, Tarim and Australasia. However, definitions of H. kristinae and morphologically closely related forms, like H. holodentata , have been interpreted rather differently by various authors. In an earlier study of this species from central New South Wales, Zhen & Percival (2004a) attempted to use the H:L ratio to distinguish H. kristinae (H:L ratio = 0.50–0.58) from H. holodentata (H:L ratio varying from 0.64 to 0.70). Subsequently more material has been made available for examination and comparison, particularly abundant specimens of both species from the Tarim Basin, which has shown that the H:L ratio is rather variable in these two species of Histiodella . H. kristinae has more recently been interpreted as having a smaller cusp with its tip lower than those of the highest denticles on the anterior process (Zhen et al., 2009b, p. 38). Following this definition of H. kristinae (more or less as originally given by Stouge, 1984), material from allochthonous limestones in the Oakdale Formation has been re-assigned to H. holodentata (Percival & Zhen, 2007; Zhen et al., 2009b). Other specimens previously referred to as H. holodentata should now also be re-assigned to H. kristinae , such as those illustrated by Rasmussen (2001) and Löfgren (2004). The specimen illustrated by Rasmussen (2001, pl. 7, fig. 19, from sample 69668) as H. holodentata seems morphologically identical with the specimen assigned to H. kristinae ( Rasmussen, 2001, pl. 8, fig. 1). This re-assignment is consistent with the information shown in figure 26 of Rasmussen (2001), where H. kristinae was recorded as occurring in sample 69668 with H. holodentata occurring in the samples immediately below, but not in sample 69668. Löfgren (2004) illustrated both H. holodentata ( Löfgren, 2004, fig. 7t from sample H6) and H. kristinae ( Löfgren, 2004, fig. 7u from sample H4) in the Kårgärde section in Sweden, but these two illustrated specimens are nearly identical and can be confidently assigned to H. kristinae .

Histiodella intertexta was introduced by An (in An et al., 1981) as a nomen nudum (Zhang, 1998c, p. 73), and the only figured specimen (designated as the holotype: An et al., 1981, pl. 1, fig. 20) is rectangular in outline and identical with the type material of H. kristinae . However, Zhang (1998c) correctly pointed out that two specimens subsequently identified and illustrated as H. intertexta by An et al. (1985, pl. 14, figs 15–16) and An (1987, pl. 18, figs 15–16, pl. 30, fig. 10) should be reassigned to H. holodentata . They show a much larger cusp which, although distally broken, would extend higher than any of the denticles on the anterior process.

The holotype of H. sinuosa (Graves & Ellison, 1941, pl. 2, fig. 13) from the Fort Peña Formation of Texas is a broken Pa element with a large, upward-pointing cusp. Based on the studies of Bradshaw (1969) and Ethington & Clark (1982), the Pa element of H. sinuosa (with H. serrata Harris, 1962 as a junior synonym) differs from both H. holodentata and H. kristinae in having a triangular outline in lateral view with the upper margins of the longer anterior and shorter posterior processes gradually declining distally (see Bradshaw, 1969, pl. 137, fig. 24; Sweet et al., 1971, pl. 1, fig. 39). Bauer (2010) treated H. sinuosa and H. serrata as separate species, indicating that small denticles were welldeveloped in the posterior process of the Pa element in H. serrata (pl. 2, fig. 16–17), but they were generally absent in the Pa element of H. sinuosa (pl. 2, fig. 19). Although the apparatus configuration of these two species and their ontogeny was well documented by McHargue (1982), specific identifications for some of the specimens previously assigned to either H. serrata or H. sinuosa by various other authors need to be reassessed (see synonymy list).

Figures

Figure 14.A–B, Histiodella holodentata Ethington & Clark, 1982. Pa element, A, NIGP 152962, Nj296, outer lateral view (IY149-023); B, NIGP 152963, Nj296, inner lateral view (IY149-024). C–F, Histiodella kristinae Stouge, 1984. Pa element; C, NIGP 152964,AFT-X- K13/13, outer lateral view (IY163-001); D, NIGP 152965, AFT-X-K13/13, inner lateral view (IY163-005); E–F, NIGP 152966,AFT-X- K13/13, E, outer lateral view (IY163-003), F, outer lateral view, close up showing fine surface striation (IY163-004). G–L, Panderodus gracilis (Branson & Mehl, 1933). G–I, tortiform element, NIGP 152967, Nj379, G, outer lateral view (IY160-024), H, outer lateral view showing furrow and fine striation on the base (IY160-025), I, inner lateral view (IY160-026). J–L, falciform element, NIGP 152968, Nj379, J, inner lateral view (IY160-027), K, outer lateral view (IY160-028), L, basal view (IY160-029). Scale bars 100 µm.