Spinatrypa subkwangsiensis ( Tien, 1938 )

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 : 801

Spinatrypa subkwangsiensis ( Tien, 1938)

Fig. 10C–G .

1938 Atrypa aspera var. subkwangsiensis sp. nov.; Tien 1938: 100–101, pl. 8: 1–4, 17.

1983 Spinatrypa subkwangsiensis (Tien) ; Chen 1983: 321, pl. 30: 5a–f.

2002 Spinatrypa subkwangsiensis ( Tien, 1938) ; Ma et al. 2002: 388, fig. 11A–E.

2005 Spinatrypa subkwangsiensis ( Tien, 1938) ; Ma et al. 2005: 441, pl. 1: 9–18.

Material.—One dorsal valve from the middle part of the Longkouchong Formation of the Qiziqiao section. About 50 specimens from the basal part of the Qilijiang Formation, most of which are complete shells.

Discussion.—The dorsal valve figured in Fig. 10C is about 12.7 mm wide and 12.4 mm long, with about 25 ribs on the whole shell surface and 4.5 ribs per 5 mm at the anterior margin, which is transitional between Spinatrypina douvillei ( Mansuy, 1912) and Isospinatrypa bodini ( Mansuy, 1912) that have respectively about 5 ribs per 5 mm and 4 ribs per 5 mm at the anterior margin (from counting on Mansuy’s 1912 illustrations). However, its seemingly spiny ornamentation and much convex dorsal valve of the studied specimen suggest that it should be assigned to Spinatrypa . It is morphologically consistent with S. subkwangsiensis Group B of Ma et al. (2002: 388, with finer and more ribs than Group A).

Relatively abundant specimens in the basal part of the Qilijiang Formation in the Qiziqiao section ( Fig. 10D–G for example) are small−sized specimens similar to those reported by Ma et al. (2005, pl.1: 9–18). They are generally less than 10 mm in width, biconvex (in specimens smaller than 8 mm in width) to medium dorsi−biconvex (in larger specimens), with about 18 ribs (for specimens of Fig. 10F, G ) and 20–25 ribs (for specimens of Fig. 10D, E ). Larger specimens show spiny bases ( Fig.10E 3 ) or traces of spines ( Fig. 10D 1 ). A submesothyrid subrounded foramen (0.5 to 0.75 mm in diameter, depending on shell size) is bounded by a pair of deltidial plates on its lower−lateral sides. These specimens of sample QZQ 4 are smaller than Spinatrypa discoforma Chen, 1983 ; they have a dorsi−biconvex profile (versus biconvex to ventribiconvex in S. discoforma ), more ribs (20–25 versus 15–20 in S. discoforma ) and a well developed foramen defined by a pair of deltidial plates (foramen and deltidial plates in S. discoforma are “obsolescent and not present” according to its original description by Chen 1983: 321–322). By comparison with similar−sized specimens of Spinatrypa subkwangsiensis Group A from the Shetianqiao section ( Ma et al. 2002), these specimens seem to possess higher but narrower ribs, much denser growth lamellae, and finer spines or spine bases. It can not be ruled out that they actually are mature specimens and represent a distinct species of Spinatrypa or Isospinatrypa , pending more material available for study and comparisons.

Occurrence.—This species is widely distributed in South China, both geographically and stratigraphically, e.g., in the Givetian–Frasnian interval of central Hunan and northern Sichuan (e.g., Tien 1938; Chen 1983; Ma et al. 2002). The studied specimens are from Beds 14 and 20 of the Qiziqiao section ( Fig. 2 ), correlated with the Palmatolepis hassi to lower part of the Early Pa. rhenana conodont zones.

Figures

Fig. 10. The spinatrypinae brachiopods from the Early and Middle Frasnian of the Caiziyan and Qiziqiao sections. A, B. Spinatrypina douvillei (Mansuy, 1912). A. PUM05018, sample GC21–24, Caiziyan section, Early Frasnian, dorsal view of an exfoliated specimen on slab. B. PUM05019, sample GC21–24, Caiziyan section, Early Frasnian, dorsal view of another exfoliated specimen on slab. C–G. Spinatrypa subkwangsiensis (Tien, 1938) Group B. C. PUM05020, sample QZQ1–3, Qiziqiao section, Middle Frasnian, dorsal view of an exfoliated specimen on slab. D. PUM05021, sample QZQ4, Qiziqiao section, probably Late Frasnian, dorsal (D1), lateral (D2), ventral (D3), posterior (D4), and anterior (D5) views of an adult(?), note spiny bases and broken spines. E. PUM05022, sample QZQ4, Qiziqiao section, probably Late Frasnian, posterior (E1), anterior (E2), ventral (E3), dorsal (E4), and lateral (E5) views of another adult (?) with a well preserved foramen bounded by a pair of conjunct deltidial plates at the bottom. F. PUM05023, sample QZQ4, Qiziqiao section, probably Late Frasnian, dorsal (F1), ventral (F2), lateral (F3), posterior (F4), anterior (F5), and enlarged area (F6) views of a juvenile with a well preserved foramen bounded by a pair of conjunct deltidial plates at the bottom. G. PUM05024, sample QZQ4, Qiziqiao section, probably Late Frasnian, anterior (G1), posterior (G2), dorsal (G3), ventral (G4), and lateral (G5) views of another juvenile. H–I. Spinatrypina lungkouchungensis (Tien, 1938). H. PUM05025, sample QZQ4, Qiziqiao section, probably Late Frasnian, ventral view, specimen is on slab. I. PUM05026, sample QZQ3, Qiziqiao section, Middle Frasnian, dorsal (I1), lateral (I2), ventral (I3), and anterior (I4) views of a juvenile.

Fig. 3. Brachiopod distribution in the Early and Middle Frasnian of South China. (from Chen 1983; 1984; Hou 1988; Sartenaer and Xu 1991; Ma et al. 2005; this study, and our unpublished data). Species of “Ningbingella” and “Ypsilorhynchus” needs confirmation of their generic status. Abbreviations: K., Klapperina; M. Mesotaxis; Pa., Palmatolepis.

Fig. 1. Geographic map of China (A) and locations of the stratigraphic sections (Δ) investigated in this study (B).

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.