Cyrtospirifer cf. sichuanensis Chen, 1978

Ma, Xue-Ping, Becker, Ralph Thomas, Li, Hua & Sun, Yuan-Yuan, 2006, Early and Middle Frasnian brachiopod faunas and turnover on the South China shelf, Acta Palaeontologica Polonica 51 (4), pp. 789-812 : 804-806

Cyrtospirifer cf. sichuanensis Chen, 1978 in Xu et al. 1978

Figs. 11E, F , 12A , 13 .

1978 cf. Cyrtospirifer sichuanensis Chen (sp. nov.); Xu et al. 1978: 374, pl. 149: 2, 3.

2003 Cyrtospirifer “ sinensis ” ( Grabau, 1931); Ma and Day 2003: 276, figs. 6.15, 6.16, 6.20–6.22, 6.24, 6.25 (not 6.19 and 6.23).

Material.— Fourteen specimens from sample QZQ1 (including nine ventral valves, three dorsal valves, and two complete shells), two fragmentary ventral valves from sample QZQ4 , and one heavily exfoliated dorsal valve from sample GQ6 of the Qifengzhen section (see figure explanation). In addition, there are about 20 relatively well preserved specimens and many broken ones from the latest Frasnian of the Xikuangshan section in central Hunan and Tien’s (1938) original specimens presumably from the Longkouchong locality for comparison .

Discussion.—Specimens from the Longkouchong Formation are mostly poorly preserved. Tien (1938) described two species of Cyrtospirifer from the same formation at this locality, here considered as one ( Ma and Day 2003). So far no specimens similar to those figured by Tien (1938) have been recovered, but Tien’s specimens are worn shells that do not have micro−ornament preserved, and a general shape similar to Sinospirifer subextensus ( Martelli, 1902) from the Early Famennian of central Hunan Province (Ma et al. 2003; Ma and Day in press). One of Tien’s specimens has a small shell area with preserved micro−ornament of the whitneyi – subextensus type (i.e., with pustules both on shell plications and in interspaces, which is typical of Cyrtospirifer whitneyi and Sinospirifer subextensus ), and a thickened ventral posterior ( Tien 1938: pl. 16: 1, specimen 6231). Two specimens ( Tien 1938: pl. 16: 2–3, specimens 6285 and 6235) are seen to have traces of a delthyrial cover that is identical with that of S. subextensus . As large−sized Frasnian Cyrtospirifer (e.g., C. “ sinensis ” in Ma and Day 2003) from South China have not been found so far to have pustule−like micro−ornament and subextensus −like delthyrial covering, it cannot be ruled out that Tien’s specimens came from the Early Famennian, and were labeled erroneously. Tien (1938) never mentioned the most common brachiopod (i.e., Desquamatia qiziqiaoensis in the present paper) from the same horizon and locality.

Two cyrtospiriferids were described from the Longmenshan section of Sichuan Province in southwestern China (Xu et al. 1978): Cyrtospirifer sinensis ( Grabau, 1931) and C. sichuanensis Chen, 1978 , but their internal structures and micro−ornament were not described. Externally the present specimens are similar to C. sichuanensis in shell size and number of sinal plications, but differ in having extended cardinal extremities. Restudy of the Late Frasnian Cyrtospirifer “ sinensis ” specimens of the Xikuangshan section shows that they do not possess a thickened ventral posterior as described by Ma and Day (2003: 276), whose description was then based on specimen PUM 98057 illustrated by fig. 6.19 from the Chongshanpu section. The present specimens are different from the Xikuangshan specimens in having fewer sinal plications (generally fewer than 10 versus generally 10–15), but shells are smaller in size. C. cf. sichuanensis is distinct from Cyrtospirifer ? variabilis Ma and Sun, 2001 from the Shetianqiao and Xikuangshan sections in its larger size and in having a distinct delthyrial plate (versus a very short delthyrial plate in Cyrtospirifer ? variabilis).

The shell is similar to Cyrtospirifer kermanensis Brice, 1999 described from Iran, but it differs in the absence of fine spines and radial striae and its adult specimens ( Fig. 11E, F ) differ in having more alate cardinal extremities.

Occurrence.—This species occurs in the Middle and Late Frasnian of South China. The studied specimens are from Beds 14 and 20 of the Qiziqiao section of central Hunan ( Fig. 2 ), correlated with the Palmatolepis hassi Zone to the lower part of the Early Pa. rhenana Zone and 17 m above the base of the “Gubi” Formation (see Zhong et al. 1992).

Figures

Fig. 11. Plicate spiriferid brachiopods from the Frasnian of the Qiziqiao and Qifengzhen sections. A. Theodossia? sp. PUM05027, sample QZQ4, Qiziqiao section, probably early Late Frasnian (cardinal extremities somewhat broken), ventral (A1), area (A2), and lateral (A3) views of a ventral valve. B–D. Cyrtospirifer? sp. B. PUM05028, sample QZQ3, Qiziqiao section, Middle Frasnian, dorsal (B1), posterior (B2), ventral (B3), lateral (B4), and anterior (B5) views of a juvenile.C. PUM05029, sample QZQ1, Qiziqiao section, Middle Frasnian, posterior (C1), lateral (C2), anterior (C3), dorsal (C4), and ventral (C5) views, note the thick shell material. D. PUM05030, sample QZQ1–3, Qiziqiao section, Middle Frasnian, ventral interior (D1), lateral (D2), and ventral exterior (D3) views, note thickened ventral posterior. E, F. Cyrtospirifer cf. sichuanensis Chen in Xu et al. (1978). E. PUM05031, dorsal view of a heavily exfoliated specimen of sample GQ6 of the Qifengzhen section in the vicinity of Guilin, about 17 m above the base of the “Gubi Formation” (Zhong et al. 1992). F. PUM05032, sample QZQ1, Qiziqiao section, Middle Frasnian, ventral view of an entirely exfoliated specimen. G. Cyrtospirifer cf. extensa Ching et Liu in Wang et al. 1982; PUM05033, sample QZQ1, Qiziqiao section, Middle Frasnian (cardinal extremities somewhat broken), anterior (G1), dorsal (G2), ventral (G3), lateral (G4), and posterior (G5) views. H. Pyramidaspirifer cf. helenae (Fenton, 1918); PUM05034, sample QZQ4, Qiziqiao section, probably early Late Frasnian, dorsal (H1), ventral (H2), lateral (H3), area (H4), and anterior (H5) views of a slightly distorted shell.

Fig. 12. A. Sinal plication pattern of Cyrtospirifer cf. sichuanensis Chen, 1978, specimen illustrated on Fig. 11F. B. Sinal plication pattern of Cyrtospirifer? sp., specimen illustrated on Fig. 11C.

Fig. 13. Transverse serial sections of Cyrtospirifer cf. sichuanensis Chen, 1978; Qiziqiao section, Middle Frasnian. Numbers refer to distance in mm from the ventral apex. A. Specimen PUM05035, numbers 1–3 on the lateral profile indicate the first three sections at ~1.0, ~2.0, 3.1 mm; acetate peel number: 05C, sample QZQ1. B. Specimen PUM05036, acetate peel number: 05E, sample QZQ1.

Fig. 2. Stratigraphy and distribution of Early and Middle Frasnian brachiopods in South China. Most but not all known brachiopods are described and illustrated in this paper. For the distribution of atrypids in the Dushan section, for example, see Ma et al. (2005). The stratigraphy of Panxi and the occurrence of Cyrtospirifer sp. are based on Yunnan compiling group (1978) and the occurrence of Stringocephalus in the lower part of the Yidade Formation is as in Xian et al. (1988: 148). The stratigraphy of Dushan and the occurrence of Stringocephalus sp. are as in Liao et al. (1979); the Caiziyan section was re−measured by Long−Ming Wei, Xue−Ping Ma, and Hua Li (personal communication 2005), with coral identifications by Wei−Hua Liao. The stratigraphy of Qiziqiao is based on data of Z.−X. Hu and Z.−Q. Deng in Tan et al. (1987), and the occurrence of Yunnanella sp. is based on Zu−Han Liu (personal communication 2001). Abbreviations: calc., calcareous; argill., argillaceous; C., Cyrtospirifer; Pa., Palmatolepis; Po., Polygnathus; S., Spinatrypina.