Jing et al.—Ordovician conodonts from Wuhai area
(Albanesi et al., 1998; Stouge, 2012) or a trimembrate apparatus (Lindström, 1964; Zhang, 1998a).
Spinodus spinatus (Hadding, 1913) Figure 9.30–9.34
2011a Spinodus spinatus (Hadding); Zhen et al., p. 310, pl. 15, figs. A–H. [see for synonymy]
Material.—Seventeen sepcimens (Table 1).
Occurrence.—W-2-2, W-4-3, W-6-1, W-7-1, W-9-2, W-9-3, W-10-3, HT-1-1, HT-6-1.
Remarks.—S. spinatus is relatively common in our samples, and its main characters have been fully described by Albanesi et al. (1998) and Zhang (1998a). Although elements representing a symmetry transition series (S elements) were widely reported for this species, its apparatus and affinities are still poorly known. Albanesi et al. (1998) suggested a seximembrate species apparatus for it, in which the P elements were differentiated from other elements by having a prominent anticusp. However, Lindström (1964) and Zhang (1998a) interpreted S. spinatus as consisting of a trimembrate apparatus (Sa, Sb and Sc), and considered that the occurrence of the anti-cusp had little significance in differentiating its element types. Zhen et al. (2011a) distinguished an Sd element for the apparatus by the feature of prominent anti-cusp. We agree with the latter viewpoint. Our specimens are identical to the corresponding S elements figured by Zhang (1998a) and Zhen et al., (2011a).
Genus Yangtzeplacognathus Zhang, 1998b
Type species.—Polyplacognathus jianyeensis An and Ding, 1982.
Remarks.—Before Yangtzeplacognathus was proposed by Zhang (1998b), species of this genus were assigned to Eoplacognathus. Yangtzeplacognathus was erected to accom- modate a group of species with unpaired, markedly dissimilar sinistral and dextral stelliplanate Pa and pastiniplanate Pb elements (Zhang, 1998b). Löfgren and Zhang (2003) recog- nized the geniculate M, alate Sa, quadriramate Sb, bipennate ScA, and tertiopedate ScB elements of the genus. Considering analogies to the other related genera with ramiform-pectiniform apparatus structures, Zhen et al. (2011a) reassigned the quadriramate and tertiopedate elements to the Sd and Sb positions, respectively.
Yangtzeplacognathus foliaceus (Fåhræus, 1966) Figure 9.35, 9.36
1998a Yangtzeplacognathus foliaceus (Fåhræus); Zhang, p. 97, pl. 19, figs. 9–12. [see for synonymy]
2011a Yangtzeplacognathus foliaceus; Zhen et al., p. 311, figs. 16–17. [see for synonymy]
Description.—The stelliplanate Pa element (Figure 9.35) has four main processes: a short, distally pointed anterior process; a relatively wide, distally pointed posterior process; a very short,
787
curved and distally blunt posterolateral process; and a bifid, well-developed but narrow antero-lateral process with a exten- ded, blade-like posterior lobe and a short anterior lobe. The anterior lobe of the anterolateral process and the anterior process form a acute angle about 20°, and they are of equal length and look similar to each other. The distal end of the posterolateral process curves anteriorly, although this feature is shielded mostly by debris in the figured specimen. The pastiniplanate Pb element (Figure 9.36) has a relatively long and distally blade-like anterior process, a much shorter posterior process forming an angle of about 160° with the lateral process (distally broken off). All processes of the two specimens bear a central denticle row. Most of the denticles are laterally confluent and show a ridge shape.
Material.—Two specimens (Table 1). Occurrence.—W-10-3.
Remarks.—Bergström (1983) and Zhang (1998b) considered this species to have four types of morphologically different platform elements that do not occur in mirror images, but that are unpaired, markedly dissimilar sinistral and dextral stelliplanate Pa and pastiniplanate Pb elements. Unfortunately, we only obtained two types of them, sinistral Pa (figure 9.35) and sinistral Pb (figure 9.36). Our specimens correspond to the E. foliaceus-E. reclinatus transition of Bergström (1983) and Yangtzeplacognathus foliaceus of Zhen et al. (2011a) in some respects, such as outline of sinistral Pa element and awide-angle formed by the short posterior process and the lateral process of sinistral Pb element. Following the suggestions of Zhen et al. (2011a), both elements described above are tentatively assigned to this taxon.
Acknowledgments
This study was supported by the “973-Program” project of China (No. 2011CB403001). We are very grateful to S.M. Bergström, Y.Y. Zhen, S.A. Leslie, and B. Pratt for read- ing the manuscript and offering many useful comments and suggestions. We would like to express our gratitude to S. Stouge, G. Bagnoli, Z.H. Wang, and T. Tolmacheva for making valuable improvements of conodont identification. Thanks are given also to M.X. Mei and H.J. Zhang for their help on petrography, and to Z.T. Wang, Q. Fang, X.T. Song, T.T. Chuan, and L.P. Yuan for assistance within sampling.
References
Agematsu, S., Sashida, K., Salyapongse, S., and Sardsud, A., 2006, Ordovician conodonts from the Thong Pha Phum area, western Thailand: Journal of Asian Earth Sciences, v. 26(1), p. 49–60.
Agematsu, S., Sashida, K., and Sardsud, A., 2013, A new Middle Ordovician conodont fauna from the Thong Pha Phum area of western Thailand: Paleontological Research, v. 17(2), p. 179–188.
Albanesi, G.L., Hünicken, M.A., and Barnes, C.R., 1998, Bioestratigrafia, Biofacies y Taxonomia de conodontes de las secuencias Ordovicicas del cerro Porterillo, Precordillera Central de San Juan, R. Argentina: Actas de la Academia Nacianal de Ciencias, Tomo XII, p. 1–74.
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