Histiodella holodentata Ethington & Clark, 1982

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 : 227-228

Histiodella holodentata Ethington & Clark, 1982

Fig. 14A–B

Histiodella holodentata Ethington & Clark, 1982: 47–48 , pl. 4, figs 1, 3, 4, 16 (cum syn.); Nowlan & Thurlow, 1984: pl. 1, figs 1, 3, 5; Wang & Zhou, 1998: pl. 4, fig. 12; Zhang, 1998c: 72, pl. 9, figs 14–15; Zhao et al., 2000: 205, pl. 27, figs 12–14; Johnston & Barnes, 2000: pl. 15, fig. 7; Du et al., 2005: 365, pl. 1, figs 22–26, 28 (cum syn.); Agematsu et al., 2006: fig. 7.18; Chen et al., 2006: fig. 10W; Percival & Zhen, 2007: 391, pl. 1, figs 22–23; Agematsu et al., 2008b: 189, fig. 7.7; Zhen et al., 2009b: 38–39, fig. 2O; Bauer, 2010: pl. 2, fig. 9.

Histiodella tableheadensis Stouge, 1984: 87–88 , pl. 18, figs 8, 12–14, text-fig. 17; Zhang, 1998c: 72, pl. 9, figs 14, 15 (cum syn.); Albanesi & Ortega, 2003: pl. 1, fig. 4.

Histiodella intertexta An. –An et al., 1985: pl. 14, figs 15, 16; An, 1987: 154, pl. 18, figs 15, 16, pl. 30, fig. 10; Gao, 1991: 131–132, pl. 9, fig. 5.

Histiodella infrequensa An in An et al., 1983: 105–106, pl. 25, figs 1–2, text-fig. 14–12;An & Zheng, 1990: 166–167, partim only pl. 7, fig. 4, non fig. 1 (probably a broken Pa element of Rhipidognathidae ).

Histiodella kristinae Stouge. –Zhen et al., 2004a: 97–98, fig. 14A–L.

Material. Three specimens (Pa only) from one sample in the upper Dawangou Formation (see Table 1).

( Figure 12 caption, continued from facing page)… I–K, Sc element; I–J, NIGP 152941, Nj375, I, iner lateral view (IY152-017), J, basal view (IY152-018); K, NIGP 152942, Nj378, inner lateral view (IY160-009). L–N, P element; L, NIGP 152943, Nj291, inner lateral view (IY158-010); M, NIGP 152944, Nj378, inner lateral view (IY160-007); N, NIGP 152945, Nj378, outer lateral view (IY160-006). O, M element, NIGP 152946, Nj298, posterior view showing a sharp costa on the posterior face (IY159-020); P–Q, Sa element, NIGP 152947, AFT-X-K13/43, P, lateral view (IY172-009), Q, basal view (IY172-010). R –S, Drepanoistodus sp. Sa element, NIGP 152948, Nj378, R, lateral view (IY160-003), S, basal view (IY160-001). T-V, Erraticodon sp. T, Pa element, NIGP 152949, AFT-X-K13/36, posterior view (IY172-005); U, Pa element, NIGP 152950, AFT-X-K13/36, anterior view (IY172-004); V, Sc element, NIGP 152951, AFT-X-K13/36, outer lateral view (IY172-001). Scale bars 100 µm.

Remarks. This species is rare in the Dawangou material and is represented only by the Pa element, which is identical with the holotype of H. tableheadensis from the Table Head Formation of western Newfoundland (see Stouge, 1984, pl. 18, fig. 14), and the holotype of H. holodentata from the Pogonip Group of the Ibex area of Utah (Ethington & Clark, 1982). Four species of Histiodella , including H. sinuosa (Graves & Ellison, 1941) , H. holodentata , H. kristinae , and H. bellburnensis Stouge, 1984 , were recovered from the Yangjikan Section of Kalpin County, located some 50 km SW of the Dawangou section ( Du et al., 2005). These authors recognized four biozones defined by the first appearance of (in ascending order): H. sinuosa Zone , H. holodentata Zone , H. kristinae Zone , and H. bellburnensis Zone. The phylogenetic relationship of these species is therefore similar to that reported in Middle Ordovician successions of North America, such as from the Table Head Formation of Newfoundland. Stouge (1984, p. 18, text-fig. 17) demonstrated that the Histiodella lineage occurring in the Table Head Formation evolved from older species with a larger cusp and a distally declining upper margin of the anterior process, to younger species with an inconspicuous cusp and a distally raised anterior process. This same evolutionary trend among the Histiodella species was also documented by Du et al. (2005).

Histiodella infrequensa was erected by An (in An et al., 1983) based on Pa elements recovered from the Beianzhuang Formation of Tangshan, Hebei Province. The holotype ( An et al., 1983, pl. 25, fig. 1) shows a large cusp (over three times as wide as the adjacent denticles), whereas the paratype figured ( An et al., 1983, pl. 25, fig. 2) exhibits a slightly smaller cusp (about twice as wide as adjacent denticles). An’s original definition suggests that H. infrequensa is characterized by having an outline more or less quadrilateral with the L/H ratio about 3: 2 in lateral view. However, both specimens illustrated by An (in An et al., 1983) had the distal part of the cusp broken. Du et al. (2005) reassigned to H. holodentata the paratype of H. infrequensa originally illustrated by An ( An et al., 1983, pl. 25, fig. 2). An (in An et al., 1983) compared his H. infrequensa to H. sinuosa (Graves & Ellison, 1941) rather than to H. holodentata , implying that when he proposed H. infrequensa, An (in An et al., 1983) was unaware of the existence of H. holodentata . In fact the holotype of H. infrequensa is closely comparable with the holotype of H. holodentata (Ethington & Clark, 1982, pl. 4, fig. 3) except that the former shows a larger cusp. Therefore, H. infrequensa is regarded herein as a junior synonym of H. holodentata , with holotype of H. infrequensa representing an early form of this species.

Figures

Figure 12. A–Q, Drepanoistodus basiovalis (Sergeeva, 1963). A–B, M element; A, NIGP 152935, Nj378, anterior view (IY160-004), B, NIGP 152936, Nj378, posterior view (IY160-005). C–E, Sa element; C, NIGP 152937, Nj379, lateral view (IY160-039); D–E, NIGP 152938, Nj291, D, lateral view (IY158-008), E, basal view (IY158-011). F–H, Sb element; F–G, NIGP 152939, Nj379, F, inner lateral view (IY160-040), G, basal view (IY160-041); H, NIGP 152940, Nj378, outer lateral view (IY160-011)… (continued on facing page)

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.