Yuan et al.—Permian conodont taxonomy and biostratigraphy in South China
the C. inflecta Zone as the topmost Wuchiapingian conodont zone, above the C. orientalis Zone in the Dukou and Nanjiang sections. However, only a few C. inflecta specimens have been found in these two sections, and a C. inflecta population has not been recognized in many other sections. Thus, we don’t use the C. inflecta Zone in this paper.
Clarkina longicuspidata Zone.—This zone occupies the upper part of the C. orientalis Zone (Shen and Mei, 2010; Henderson, 2017), andmanyC. longicuspidata specimens are in the uppermost part of Wuchiapingian at some sections in South China. However, some specimens that have a large cusp and no brim behind the cusp and differ from C. longicuspidata and C. transcaucasica are also found below the C. orientalis Zone. In addition, C. orientalis is abundant in each sample in the C. orientalis Zone andonlya few specimens with a large cusp can be found in the lower part of the C. orientalis Zone. Thus, the first occurrence (FO) of C. longicuspidata and the basal boundary of the C. longicuspidata Zone are difficult to recognize, and the full range relationship of C. longicuspidata and C. orientalis is unclear. Here, C. orientalis, which is often found in South China, is chosen as the topmost marker of the Wuchiapingian in South China; the species also ranges into the lowest Changhsingian.
Wuchiapingian Clarkina species lineage
Clarkina, the dominant conodont genus of Lopingian strata, was established by Kozur (1989). Its characters and major difference from Mesogondolella, Jinogondolella,and Neogondolella,have been discussed in detail byKozur (1989), Wardlaw andMei (1998), Henderson and Mei (2007), and Yuan et al. (2014a). Although its origins are not well understood, most people have hypothesized that it evolved from Jinogondolella (Wardlaw and Mei, 1998; Henderson and Mei, 2007;Wardlaw and Nestell, 2010). The first species/subspecies belonging to the genus
Clarkina is Clarkina postbitteri hongshuiensis, which is considered to have evolved directly from Jinogondolella. Based on the specimens from the Penglaitan Section in South China, Henderson et al. (2002) considered that Clarkina postbitteri hongshuiensis evolved from Jinogondolella granti. However, based on specimens from West Texas, Wardlaw and Mei (1998) and Wardlaw and Nestell (2010) considered that Clarkina postbitteri hongshuiensis evolved from Jinogondolella crofti or J. altudaensis. Wardlaw and Nestell (2010) illustrated only two specimens identified as Clarkina postbitteri hongshuiensis from the Apache Mountains, West Texas; they coexist with abundant Jinogondolella altudaensis in the same samples. They still have a broad platform, dense denticles, and a very small cusp, which are characters typical within sample populations of J. altudaensis. Thus, we do not regard them as Clarkina postbitteri hongshuiensis. Wardlaw and Nestell (2010) also illustrated several
specimens of Jinogondolella granti. Those specimens have a small cusp, no obvious serrations, a broad platform, and the widest point of platform is in the middle part of platform, which are very different from J. granti. Thus, we do not interpret them as J. granti. In addition, according to our unpublished Guadalupian conodont data fromWest Texas and South China,
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the topmost zone in West Texas is near the J. prexuanhanensis Zone, and no transitional population from J. altudaensis to Clarkina postbitteri hongshuiensis has been found. Therefore, the evolutionary relationship between Jinogondolella altudaensis and Clarkina postbitteri hongshuiensis cannot be demonstrated based on the West Texas specimens. Some transitional forms with a relatively narrow platform
and nearly parallel lateral margins between Jinogondolella granti and Clarkina postbitteri postbitteri appear to exist in the Clarkina postbitteri postbitteri population at Penglaitan (e.g., Fig. 4.10, 4.11), although we did not recognize a transitional population with abundant individuals from Jinogondolella granti to Clarkina postbitteri hongshuiensis or Clarkina postbitteri postbitteri due to the rapid transition between Jinogondolella and Clarkina. Thus, based on the strata and conodont sample sequences (Henderson et al., 2002), the most suitable ancestor of Clarkina postbitteri hongshuiensis is Jinogondolella granti at the Penglaitan Section in South China. “Mesogondolella” omanensis, which has weak serrations
or no serration and is reported near the Wordian-Capitanian boundary, might be another choice for the ancestor of Clarkina in terms of outline of platform and characteristics of denticles. However, a major shortcoming is the lack of transitional forms in a long interval between “Mesogondolella” omanensis and Clarkina, but this may be related to migration. Mei et al. (1994a, b, 1998a) postulated two possible lineages
of the Wuchiapingian Clarkina species: (1) Clarkina postbitteri– C. dukouensis–C. asymmetrica–C. leveni–C. guangyuanensis– C. transcaucasica–C. orientalis lineage, and (2) C. dukouensis–C. daxianensis–C. liangshanensis–C. inflecta lineage. The first lineage is important for stratigraphic correlation because distinctive carinal variation identifies those species. The biggest challenge to the lineage is the evolutionary relationship between C. transcaucasica and C. orientalis. Clarkina transcaucasica originally was estab- lished as a subspecies ofC. orientalis (C. orientalis transcaucasica), and later was named as a direct ancestor species of C. orientalis (Gullo and Kozur, 1992; Mei et al., 1998a). However, based on some transitional specimens (e.g., Shen, 2007, fig. 5.1, 5.4, 5.7), C. orientalis more likely evolved fromC. liangshanesis basedonthe posteriorly gradual decrease in carina height in C. liangshanensis (Shen, 2007). Clarkina longicuspidata, the ancestor of the Changhsingian Clarkina species,was considered to first occur in the upper part of the C. orientalis Zone by Mei et al. (1994a) and Shen andMei (2010).However, some specimens with a large cusp and no brim behind the cusp coexist withC. transcaucasica orC. orientalis in the C. transcaucasica and basal part of C. orientalis zones. Thus, C. longicuspidata could have evolved from early Wuchiapingian Clarkina species by transitional forms. Therefore, the two most reliable Clarkina lineages in
Wuchiapingian are: (1) Clarkina postbitteri hongshuiensis–C. postbitteri postbitteri–C. dukouensis–C. asymmetrica–C. leveni– C. guangyuanensis–C. transcaucasica,and (2) C. liangshanensis– C. orientalis.
Remarks on the GLB interval
The global end-Guadalupian regression formed a major low- stand systems tract (LST) and caused widespread erosional truncation around Paleotethys, as well as in most regions of
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