Eoplacognathus crassus

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 : 254-260

publication ID	https://doi.org/ 10.3853/j.0067-1975.63.2011.1586
persistent identifier	https://treatment.plazi.org/id/03CCEB77-FFE3-634B-FCD1-FC1190FDFD4E
treatment provided by	Felipe
scientific name	Eoplacognathus crassus
status

Treatment

Yangtzeplacognathus crassus

(Chen & Zhang in Wang, 1993)

Figs 28A–O View Figure 28 , 29A–O View Figure 29

Ambalodus pseudoplanus Viira. –Ni & Li, 1987: pl. 55, fig. 16.

Eoplacognathus pseudoplanus (Viira) .–Viira et al., 2001: fig. 8a–l, 8q-t; Wang et al., 1996: pl. 4, fig. 6.

Amorphognathus variabilis (Sergeeva) .–Wang et al., 1996: pl. 4, fig. 17.

Eoplacognathus crassus Chen & Zhang in Wang, 1993: 174, pl. 37, figs 12–17; Zhang, 1997: 61–65, figs 2A–B, 3A–L, 4A–L (cum syn.); Bergström & Wang, 1998: 91–93; Wang & Zhou, 1998: pl. 1, fig. 2,?pl. 4, fig. 8; Wang & Bergström, 1999 a: 335, pl. 3, fig. 16; Wang & Bergström, 1999 b: pl. 2, fig. 14; non Xiong et al., 2006: 368, pl. 1a–b = element of Dzikodus .

Yangtzeplacognathus crassus (Chen & Zhang) .–Zhang, 1998c: 96–97, pl. 20, figs 5–8 (cum syn.); Löfgren, 2003: fig. 8A–D; Löfgren & Zhang, 2003: 731–735, figs 6, 12 (cum syn.); Viira, 2011: fig. 9B.

Material. 63 specimens from two samples of the Dawangou Formation (see Table 1).

Remarks. Specimens from the Dawangou Formation are identical with those previously documented from the Guniutan Formation in South China (Chen & Zhang in Wang, 1993; Zhang, 1998c) and from Sweden (Löfgren, 2003; Löfgren & Zhang, 2003). Chen & Zhang (in Wang, 1993) recognized two types of pectiniform (Pa = stelliplanate = polyplacognathiform, and Pb = pastiniplanate = ambalodiform) elements, each of which also has morphologically distinctive and consistent sinistral and dextral variants, based on study of the type material of this species from the Guniutan Formation in Tangshan, near Nanjing. Detailed study of the pectiniform elements of this species from China and Baltoscandia led Zhang (1997) to suggest that Y. crassus had a restricted age range that was important for international stratigraphic correlation.

Yangtzeplacognathus jianyeensis (An & Ding, 1982)

Figs 30A–L View Figure 30 , 31A–L View Figure 31

Polyplacognathus miaopoensis An et al., 1981 : pl. 1, fig. 25 (nomen nudum); Zeng et al., 1983: pl. 12, fig. 26; An et al., 1985: 44–45, partim only pl. 18, figs 13–14, non figs 8, 15 = Y. protoramosus ; Ni & Li, 1987: pl. 55, fig. 6, pl. 59, fig. 36.

Eoplacognathus cf. reclinatus (Fåhraeus) .– Ni, 1981: pl. 1, fig. 32.

Polyplacognathus jianyeensis An & Ding, 1982: 9 , pl. 3, figs 1–7; An & Xu, 1984: pl. 3, figs 18–19; An et al., 1985: pl. 18, figs 16–18.

Eoplacognathus ramosus Chen et al., 1983: 135 , pl. 1, figs 1–4.

Eoplacognathus jianyeensis (An & Ding) .–Chen & Zhang, 1984a: 329, pl. 1, figs 5–7, 12–14, 17–18, pl. 2, figs 3–4; Chen & Zhang, 1984b: 127, pl. 1, figs 30–33; An, 1987: 149, pl. 27, figs 1–7, 9–10; Chen & Zhang, 1989: 220, pl. 2, figs 26–29; Ding et al. in Wang, 1993: 175, pl. 31, figs 1–9; Wang & Zhou, 1998: partim only pl. 1, figs?3, 10, non figs 5, 7–8 = Y. protoramosus ; Dong & Wang, 2006: 149, pl. 7, figs 2, 5–6.

Eoplacognathus protoramosus Chen, Chen & Zhang. –Xiong et al., 2006: pl. 1, fig. 13.

Yangtzeplacognathus jianyeensis (An & Ding) .–Zhang, 1998b: 28, fig. 5M–S, fig. 6C, fig. 11C3, fig. 13; Zhang, 1998c: 99, pl. 19, figs 1–4 (cum syn.).

Material. 176 specimens from 12 samples (see Tables 1–2).

Remarks. Zhang (1998b) provided detailed description of this species as consisting of sinistral and dextral Pa (stelliplanate) and Pb (pastiniplanate) elements. It is characterized by the Pb element having four processes including a very short, narrow and downwardly-bent anterior process.

The nomenclatural history of this species is particularly confused. An & Ding (1982) erected Polyplacognathus jianyeensis as consisting of sinistral and dextral Pb (ambalodiform) and a Pa (polyplacognathiform) elements, with the type material recovered from the Datianba Formation of Tangshan, Jiangsu Province. Polyplacognathus miaopoensis was introduced into the literature without diagnosis or description as a nomen nudum by illustration of a designated holotype (sinistral Pb element) recovered from the Miaopo Formation of Xingtan, Hubei Province ( An et al., 1981, pl. 1, fig. 25). Later, An et al. (1985, p. 44) provided the diagnosis and description for Eoplacognathus miaopoensis based on the Pb element only, indicating that its Pa element was not recovered at the time, but in the illustration they also included a dextral Pa element (An et al., 1985, pl. 18, fig. 8), which is actually referable to Y. protoramosus (see Zhang, 1998b, p. 25). Thus An et al. (1985) not only considered E. miaopoensis and P. jianyeensis to represent separate species, but also to belong to different genera. Chen et al. (1983) proposed Eoplacognathus ramosus as consisting of sinistral and dextral Pa (polyplacognathiform) and Pb (ambalodiform) elements based on type material from the Datianba Formation of Tangshan, near Nanjing (same type locality as that of Y. jianyeensis and Y. protoramosus ), and regarded P. miaopoensis as an invalid senior synonym (nomen nudum) of E. ramosus . An (1987) revised Y. jianyeensis as a species of Eoplacognathus by regarding both P. miaopoensis and E. ramosus as synonymous, but followed the original definition given by An & Ding (1982) without differentiation of the sinistral and dextral Pa elements in the species apparatus as Chen et al. (1983) had documented.

Based on a collection of over 200 specimens from central China, Zhang (1998b) revised Y. crassus as the type species of the new genus Yangtzeplacognathus, consisting of unpaired markedly dissimilar sinistral and dextral Pa (stelliplanate) and Pb (pastiniplanate) elements, and distinguished it from other species of Yangtzeplacognathus by having Pb elements with four processes .

Yangtzeplacognathus protoramosus ( Chen, Chen & Zhang, 1983)

Fig. 32A–G View Figure 32

Eoplacognathus protoramosus Chen, Chen & Zhang, 1983: 135–136 , pl. 1, figs 7–10; An, 1987: 149–150, pl. 27, figs 11–13, 17–18; Ding et al. in Wang, 1993: 175, partim, only pl. 32, figs 1–6 (cum syn.).

Yangtzeplacognathus protoramosus (Chen, Chen & Zhang) .– Zhang, 1998c: 25–27, fig. 5E–L, fig. 6B, fig. 12 (cum syn.).

Eoplacognathus miaopoensis An et al. –An et al., 1985: 44–45, partim only pl. 18, figs 8, 15.

Eoplacognathus jianyeensis (An & Ding) .–Wang & Zhou, 1998: partim only pl. 1, figs 5, 7–8.

Eoplacognathus foliaceus (Fåhraeus) .–Wang, 2001: 352, pl. 1, fig. 9.

Material. 24 specimens from eight samples (see Tables 1–2).

Remarks. Chen et al. (1983) erected E. protoramosus as consisting of sinistral and dextral Pa (polyplacognathiform) and Pb (ambalodiform) elements based on material from the Datianba Formation of Tangshan, near Nanjing, and regarded it as the most distinctive species defining their E. protoramosus Subzone in the upper part of the P. serra Zone. Zhang (1998c) indicated that this species had a stratigraphic range limited to the upper part of P. serra Zone in South China, but in the collections from the Dawangou section it has also been reported from the basal part of the Kanling Formation (Sandbian, anserinus Zone ). The figured dextral Pb element ( Fig. 32B View Figure 32 ) from the base of the Kanling Formation (sample AFT-X-K13/40) is identical with the specimen illustrated by Zhang (1998c, fig. 5J, fig. 12F) representing the late form of this species. In the Dawangou section Y. protoramosus is relatively uncommon, but extends well into the anserinus Zone. Zhao et al. (2006, p. 196) also recorded Y. protoramosus in the anserinus Zone at Lunnan in the Tarim Basin.

ACKNOWLEDGMENTS. YYZ’s study was supported by the CAS / SAFEA International Partnership Program for Creative Research Teams. Part of the material studied in this contribution was collected by ZHW during 1987 with the support of a State Scientific Research Project on the correlation of the Phanerozoic strata in the Tarim Basin. Field work and collecting in the Tarim Basin during 2008 and processing of half of each sample was undertaken with the support of research grants to YDZ (2008ZX05008-001–001). Prof. Zhang Shiben from Petrol China is thanked for his guidance in the field work in 2008. Gary Dargan (formerly of Geological Survey of New South Wales , Londonderry ) assisted with acid leaching and residue separation of the remaining half of each sample collected in 2008. Dr Viive Viira from Estonia is thanked for providing the senior author with her valuable monograph and for useful discussions on the type specimens of Polonodus clivosus . Scanning electron microscope photographs were prepared in the Electron Microscope Unit of the Australian Museum (Sydney). J. Repetski and R. L. Ethington are thanked for their careful and constructive reviews of the manuscript. IGP publishes with permission of the Executive Director, NSW Office of Resources and Energy .