Desquamatia qiziqiaoensis, Ma & Becker & Li & Sun, 2006

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 : 799-801

Desquamatia qiziqiaoensis sp. nov.

Figs. 8 , 9 .

1978? Desquamatia (Synatrypa) kimberleyensis ( Coleman, 1951) ; Grey 1978: 20–33, pl. 2: 2–3.

2005 Desquamatia (Desquamatia) cf. minor ( Chen, 1983) ; Ma et al. 2005: 443–445, text−fig. 5, pl. 2: 6–15 (not others).

Holotype: PUM05014 ( Fig. 8C ), a complete adult shell.

Type horizon: Middle part of the Longkouchong Formation, bed 14 of

Tan et al. (1987) or bed 3 of Yu et al. (1990: 96), Middle Frasnian.

Type locality: On the north side of a railway near the Qiziqiao railway station, Hunan Province, China.

Etymology: From the name of the locality, where it is most abundant.

Diagnosis.—Small sized Desquamatia with about 9–10 costae per 5 mm at the anterior margin, weakly dorsi−biconvex, tiny dental cavities or nuclei. From the most similar Desquamatia minor Chen, 1983 differs in having tiny dental cavities. From D. schroeteri differs in having slightly denser growth lammellae, denser costae, and narrower interspaces.

Material.— Sample PY 5 from the Panxi section, probably Middle Frasnian (18 specimens). About 150 specimens from the Longkouchong Formation of the Qiziqiao section (about 85 various sized specimens were collected from a 5 cm thick layer in an area of 20 × 40 cm for sample QZQ3 ) .

Description.—Shell small, generally 20–25 mm wide in adults; hinge slightly curved, about 1/2 and 2/3 width of shell in large and small specimens, respectively; suboval in shape, weakly dorsi−biconvex in lateral profile; anterior commissure rectimarginate in small specimens and somewhat strongly uniplicate in specimens over 20 mm wide. Surface covered with fine costae, about 9–10 costae per 5 mm at anterior margin; costae rounded, separated by furrows of narrower to equal width; increase of number of costae on ventral valve chiefly by bifurcation and on dorsal valve chiefly by intercalation. Variably spaced growth lamellae, generally about 5 per 5 mm to as many as 10 per 5 mm. Ventral beak normally slightly incurved, interarea small, with a pair of deltidial plates bounding a small submesothyrid foramen (about 0.75 mm in diameter for both specimens PUM 05014 in Fig. 8C and PUM 05015 in Fig. 8D ) on its lower−lateral sides.

Internally secondary shell thickening distinct ( Fig. 9 ). Ventral valve with incised muscle field; very tiny dental cavities, or dental nuclei; teeth strong, each with a well−developed accessory lobe. Dorsally, muscle field with a low, centrally grooved median ridge; inner socket ridges distinct, middle socket ridges low but robust, outer socket ridges indistinct; crural bases small, arising from tips of supporting socket plates (term used as Copper 2002: 1381, fig. 933); crura relatively strong, feathered, rapidly widened laterally in cross section.

Discussion.—These specimens are not regarded as juveniles or younger specimens of Desquamatia cf. kimberleyensis because the younger portion of the latter shell still seems to possess coarser costae than our new species. Grey’s own figured specimens of D. kimberleyensis ( Grey 1978: pl. 2: 2–3, specimens GSWA F9541 and F9542) possess finer and more numerous costae (10 costae per 5 mm at the anterior margin) than the holotype and are similar to the present species from South China in terms of external morphology (rib number and small straight interarea), rather than to the type specimens of D. kimberleyensis . D. qiziqiaoensis differs from D. kimberleyensis ( Coleman, 1951) in its 9–10 costae versus 7–8 per 5 mm.

Sectioning has not revealed spiralia (the figured specimen herein has been ground to near mid−length), otherwise it is similar to D. cf. kimberleyensis internally. Externally it can be distinguished from the latter by its smaller size, finer and more numerous costae (generally 9–10 costae per 5 mm in the present species versus 7–8 costae per 5 mm in D. cf. kimberleyensis ). The new species differs from D. minor Chen, 1983 (compare with Chen 1983: 288, fig. 22) and D. cf. minor from Guizhou Province of South China (compare with Ma et al. 2005: 443, fig. 4) in its tiny dental cavities (versus large dental cavities in the latter two). It also differs from D. schroeteri Copper, 1967 in having somewhat denser growth lamellae, denser costae, and narrower interspaces.

Occurrence.—Abundant in Bed 14 of the Qiziqiao section ( Fig. 2 ), correlated with the Early Palmatolepis hassi conodont Zone; it is also present in the middle part of the Yidade Formation of the Panxi section ( Fig. 2 ).

Figures

Fig. 8. Atrypid Desquamatia qiziqiaoensis sp. nov. from the Middle Frasnian of the Panxi and Qiziqiao sections. A. PUM05012, sample PY5, Panxi section, probably Middle Frasnian, dorsal (A1), ventral (A2), posterior (A3), anterior (A4), and lateral (A5) views showing the general shape of a silicified specimen, 22.2 mm wide, 20.6 mm long, 12.9 mm thick. B. PUM05013, sample PY5, Panxi section, probably Middle Frasnian, ventral view showing nature of ribbing and concentric growth lamellae of a non−silicified specimen, 19.9 mm wide, 19.3 mm long, 11.8 mm thick. C. PUM05014 (holotype), sample QZQ1–3, Qiziqiao section, Middle Frasnian, dorsal (C1), ventral (C2), lateral (C3), posterior (C4), and anterior (C5) views. D. PUM05015, sample QZQ3, Qiziqiao section, Middle Frasnian, posterior (D1), anterior (D2), dorsal (D3), ventral (D4), and lateral (D5) views. E. PUM05016, sample QZQ3, Qiziqiao section, Middle Frasnian, dorsal (E1, E5), ventral (E2, E7), posterior (E3), anterior (E4), and lateral (E6) views.

Fig. 9. Transverse serial sections of Desquamatia qiziqiaoensis sp. nov. Specimen PUM05017 (24.3 mm wide, 24.6 mm long, and 11.8 mm thick), acetate peel number: 05B, sample QZQ3, Qiziqiao section, Middle Frasnian. Numbers refer to distance in mm from the ventral apex.

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.