Early Cambrian lingulate brachiopods from the Shaanxi Province, China

GFF volume 126 (2004), pp. 193–211.

Article

Early Cambrian lingulate brachiopods from the Shaanxi Province, China GUOXIANG LI1 and LARS E. HOLMER2 Li, G. & Holmer, L.E., 2004: Early Cambrian lingulate brachiopods from the Shaanxi Province, China. GFF, Vol. 126 (Pt. 2, June), pp. 193–211. Stockholm. ISSN 1103-5897.

Abstract: A diverse fauna of lingulate (Subphylum Linguliformea, Class Lingulata) brachiopods is described from the Early Cambrian (Qiongzhusian Stage) carbonates in southern Shaanxi Province (Fucheng and Xiaoyang sections), China. Eight species assigned to 6 genera are systematically described. Among them, the taxa assigned to the Superfamily Linguloidea comprise Palaeobolus liantuoensis Zeng, Lingulellotreta malongensis (Rong), Eoobolus aff. viridis (Cobbold), Eoobolus? shaanxiensis sp. nov., and Kyrshabaktella? sp. Only Palaeobolus liantuoensis and Lingulellotreta malongensis were known previously from South China, where the latter species occurs in the soft-bodied Chengjiang fauna with preserved pedicle. The Superfamily Acrotheloidea is represented only by the new species Botsfordia minuta. The fauna also includes two primitive acrotretoid (Superfamily Acrotretoidea) species belonging to the new genus and species Eohadrotreta zhenbaensis and E. zhujiahensis; the ontogeny of Eohadrotreta supports the view that the acrotretid muscle system and ontogeny are derived in relation to the lingulide musculature and ontogeny. The fauna from Shaanxi is the oldest known diverse lingulate brachiopod assemblage from China. Keywords: Brachiopoda, Lingulata, Early Cambrian, Shaanxi Province, China. 1

Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China; [email protected] 2 Uppsala University, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, SE-752 36 Uppsala, Sweden; [email protected]. Manuscript received 4 April 2003. Revised manuscript accepted 27 January 2004.

Introduction Early Cambrian lingulate brachiopods in China have only been intermittently studied since the early of the last century (e.g. Mansuy 1912; Sun 1924), but most of these studies dealt with specimens recovered from siliciclastic rocks. Among these reports, specimens with soft-bodied preservation from the Chengjiang Lagerstätten provide a good opportunity for studying the body plans and palaeoecology of early Cambrian brachiopods (Jin et al. 1991, 1993; Jin & Wang 1992). Although lingulate brachiopods are also a relative common part of the Early Cambrian fauna in carbonate rocks of China, they have been largely neglected. Some works have recorded the existence of abundant lingulate specimens in etching residues from Lower Cambrian carbonates with other skeletal fossils (e.g. Xie 1988; Shu 1990), but no detailed taxonomic work has been done. The purpose of the present paper is to describe the first and oldest-known well-preserved and diverse fauna of lingulate brachiopods from the Lower Cambrian (Qiongzhusian stage) carbonate successions of the Fucheng and Xiaoyang sections in southern Shaanxi Province, China.

Localities and stratigraphy The specimens studied here were collected from limestones in the uppermost Guojiaba and basal Xiannüdong formations in the

Fucheng section, which is near the town of Fucheng, Nanzheng County, and from dolostones and limestones in the Xihaoping Member and the lower Shuijingtuo Formation in the Xiaoyang section, at Xiaoyang, Zhenba County, southern Shaanxi Province (Fig. 1). Both sections are situated on the present-day northern margin of the Yangtze Platform. The Xiaoyang section. – The upper Neoproterozoic and Lower Cambrian stratigraphic successions at the Xiaoyang section are well exposed. In ascending order, the stratigraphic successions (Fig.2) comprise the Xihaoping Member [also sometimes called the Huoshaodian Member (Wang & Xu 1987), but Qian (1999) considered the sequence similar to that in the Xihaoping section, Fangxian County, Hubei Province] which consists of the Dengying Formation, the Shuijingtuo and Shipai formations. The basal Cambrian Xihaoping Member consists predominantly of light dolomites and limestones with abundant skeletal fossils, including phosphatic brachiopods, sponge spicules, molluscs, cambroclaviids, hyolithelminths, etc. The Xihaoping Member (8.37 m thick) disconformably overlies the upper dolomite member of the Dengying Formation, and is disconformably overlain by the Shuijingtuo Formation. The Shuijingtuo Formation can be subdivided into two members. The 85 m thick upper member consists mainly of fine sandstones and siltstones with a few in-

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Fig. 1. Location of the Fucheng (1) and Xiaoyang (2) outcrops in the Shaanxi Province.

tercalated thin limestone beds, and contains scarce skeletal fossils. The 31 m thick lower member consists of dark thin-bedded siltstones, mudstones and limestones, and contains abundant skeletal fossils, including eodiscid trilobites, brachiopods, protoconodonts and a conodont-like fossil (Rhombocorniculum cancellatum), microdictyoniid plates, sponge spicules, etc. Most of the lingulate taxa studied here were obtained from this section. Eoobolus aff. viridis (Cobbold), Eoobolus? shaanxiensis sp. nov., and Kyrshabaktella? sp., were collected from the Xihaoping Member, while Palaeobolus liantuoensis Wang, Lingulellotreta malongensis (Rong), Botsfordia minuta sp. nov. and Eohadrotreta zhenbaensis gen et sp. nov. came from the lower Shuijingtuo Formation. Based on the small shelly fossils, the Xihaoping Member has been considered as middle Qiongzhusian stage in age (Qian 1999). Although no complete trilobite specimens have been found, the senior author (Li) has recovered the librigenal spines of trilobites through etching of the carbonate samples with acetic acid. The occurrence of librigenal spines indicates that the Xihaoping Member could be correlated with the lower or middle Qiongzhusian stage. Therefore, the correlation of the lower Xihaoping Member with the Shiyantou Member (Meishucunian stage) in eastern Yunnan (Wang & Xu 1987) is rejected here. Based on the eodiscid trilobites, bradoriids and small shelly fossils, the lower Shuijingtuo Formation is commonly correlated with the upper Qiongzhusian stage, and the upper Member is often correlated with the lower Canglangpuan stage (Shu 1990; Xie 1988). But the boundary between the Qiongzhusian and Canglangpuan stages at the Xiaoyang section is uncertain. The Fucheng section. – In the Fucheng section, the stratigraphical succession from the upper Neoproterozoic Dengying Formation to the Lower Cambrian Yanwangbian Formation is well exposed, although the lowermost Cambrian Kuanchuanpu Formation, which varies in extent geographically, is absent

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there. The Lower Cambrian succession consists, in ascending order, of the Guojiaba, Xiannüdong, and Yanwangbian formations (Fig. 2). The Guojiaba Formation, about 348 m thick, is mainly dark siliciclastic siltstone, mudstone, and shale, and disconformably overlies the dolostones of the upper Sinian Dengying Formation. In the uppermost part of the Guojiaba Formation there are several bioclastic limestone beds and nodule layers. These limestone intercalations contain abundant skeletal fossils including hyolithelminths, sponge spicules, bradoriids, phosphatic micro-brachiopods, isolated plates of Microdictyon fuchengense Li, and Sphenothallus (Li 2000; Li & Zhu 2001). The Xiannüdong Formation, about 143 m thick, conformably overlies the Guojiaba Formation, and can be subdivided into two members. The 70 m-thick lower member consists mainly of bioclastic packstones and marly limestones intercalated with oolitic limestones. It contains abundant fossils including archaeocyathans, calcified algae, phosphatic microbrachiopods, and Sphenothallus. Together with calcified algae (Girvanella, Epiphyton and Renalcis), the archaeocyathans occur in six discrete bioherm beds (Ye et al. 1996; Yuan et al. 2001). The 73 mthick upper member consists mostly of oolitic limestones intercalated with dolomitic limestones and bioclastic packstones. Conformably overlying the Xiannüdong Formation is the Yanwangbian Formation, which consists mainly of sandstones and siltstones. The only lingulate recorded from this locality is Eohadrotreta zhujiahensis gen. et sp. nov., which occurs in the uppermost Guojiaba and basal Xiannüdong formations. The upper part of the Guojiaba Formation can be correlated with the Yu’anshan Formation (Qiongzhusian Stage) of eastern Yunnan Province (Luo et al. 1994), as both Wutingaspis and Yunnanocephalus, two characteristic trilobites of the Qiongzhusian Stage in eastern Yunnan, occur in the upper Guojiaba Formation (Zhou & Yuan 1980; Chen & Zhang 1987). This correlation is further supported by the occurrence of Microdictyon plates in the uppermost Guojiaba Formation and soft-bodied Microdictyon specimens (part of the Chengjiang Lagerstätte) in the upper Yu’anshan Formation (Chen et al. 1989). The precise location of the base of the Qiongzhusian Stage (i.e., the Meishucunian-Qiongzhusian boundary) in the Guojiaba Formation is uncertain. The overlying Xiannüdong Formation, the type section of which is located near the village of Shatan in Nanjiang County, northern Sichuan Province (Li et al. 1975), crops out at a number of localities on the northern margin of the Yangtze Platform (in southern Shaanxi and northern Sichuan provinces). Due mainly to preservation-related problems in the identification of trilobites collected from this rock unit, its age has variously been interpreted as upper Qiongzhusian or lower Canglangpuan. In eastern Yunnan Province, where the stratotype sections of the Qiongzhusian and Canglangpuan stages are located, the Qiongzhusian Stage can be subdivided into two trilobite biozones (in ascending order, the Parabadiella and Eoredlichia– Wutingaspis biozones; Luo et al. 1994), while the overlying Canglangpuan Stage can be subdivided into four biozones (in ascending order, the Yiliangella, Drepanuroides, Palaeolenus, and Megapalaeolenus biozones; Luo et al. 1994). Based on examination of the Shatan section, Zhou & Yuan (1980) provisionally placed the Xiannüdong Formation in the upper Qiongzhusian Stage, citing in support the presence of the basal part of the Yanwangbian Formation (with the trilobites Yiliangella, Shatania, and Pseudoredlichia), and the occurrence of the trilo-

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Fig. 2. Lithological columns from the Fucheng and Xiaoyang outcrops, with sampled intervals.

bites Wutingaspis, Yunnanocephalus, Malungia, and Zhenbaspis in the upper part of the Guojiaba Formation. Based on work conducted in Xixiang and Nanzheng counties, southern Shaanxi Province, Chen & Zhang (1987) placed the Xiannüdong Formation in the lower Canglangpuan Stage, citing the occurrence of the trilobites Malungia and Yiliangella in the lower part of the Xiannüdong Formation, and the trilobites Drepanopyge and Drepanuroides in the basal part of the Yanwangbian Formation. Yuan et al. (2001) placed the lower Xiannüdong Formation in the upper Qiongzhusian Stage (Eoredlichia-Wutingaspis biozone), citing the occurrence of the trilobites Zhenbaspis, Eoredlichia, Kuanyangia, Yunnanocephalus, Malungia, and Eomalungia in the lower member of the Xiannüdong Formation in the Fucheng section.

Systematic paleontology The studied material was obtained from phosphatic limestones, dolostones, and limestones. All samples were digested with 5– 10% solution of acetic acid for three to seven days. A sieve of 0.074 mm meshes was used to reduce the bulk of residues. Afterwards, skeletal fossils were manually picked from the insoluble residues under a binocular microscope. Selected fossils were then mounted on stubs using double-sided sellotape, and coated with palladium-gold alloy in a Jeol JFC-1100 sputter. Thereafter, the specimens were examined and photographed under a Jeol JSM-35CF Scanning Electron Microscope (SEM) with acceleration voltage of 15 or 20 Kv.

All specimens described or photographed are deposited in Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGP).

SUBPHYLUM LINGULIFORMEA WILLIAMS, CARLSSON, BRUTON, HOLMER & POPOV, 1996 CLASS LINGULATA GORJANSKY & POPOV, 1985 ORDER LINGULIDA WAAGEN, 1885 SUPERFAMILY LINGULOIDEA MENKE, 1828 FAMILY OBOLIDAE KING, 1846 SUBFAMILY OBOLINAE KING, 1846 Genus Palaeobolus Matthew, 1899 Type species. – Palaeobolus bretonensis Matthew, 1899; Middle Cambrian (Amgian, Bourinot Group), Cape Breton, Canada. Diagnosis. – See Holmer et al. (2001, p. 42).

Palaeobolus liantuoensis Zeng, 1987 Figs. 3, 4A–E, 5, Tables 1, 2 Synonymy. – • 1983 Palaeobolus bretonensis Matthew – Gorjansky & Koneva, p. 130, pl. 27, figs. 1–14 [non Matthew, 1899]. • 1987 Palaeobolus liantuoensis n. sp. – Zeng, p. 209, pl. 8, 9–13, text-fig. 5–1. • 2001 Palaeobolus liantuoensis Zeng – Holmer et al., p. 44, pl. 9, 1–13.

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Material. – 11 complete shells, 53 dorsal and 77 ventral valves, the lower Shuijingtuo Formation, Xiaoyang section. Diagnosis. – See Holmer et al. (2001, p. 44). Description of specimens from Shaanxi. – Shell slightly inequivalved, almost equibiconvex. Both valves with median sulcus. Ventral valve on average 120% as long as wide with acute, slightly acuminate beak. Pseudointerarea orthocline, triangular, on average 51% as long as wide, and occupying 58% of valve width. Pedicle groove deep with subparallel lateral margins. Propareas flattened, raised above the valve floor, with flexure lines. Dorsal valve with rounded outline, on average 113% as long as wide. Pseudointerarea close to orthocline, low, on average 37% as long as wide, and occupying more than half of valve width. Median groove broad, shallow, on average 41% of width of pseudointerarea. Flexure lines poorly developed. Ventral interior with weakly impressed visceral area, extending to mid-valve. Pedicle nerve impression poorly visible. Muscle scars poorly impressed and not clearly differentiated. Ventral vascula lateralia with straight, divergent proximal parts. Dorsal interior with weakly impressed visceral area, bisected by short median septum and median tongue, not extending to mid-valve. Muscle scars and impressions of mantle canals poorly visible apart from possible imprints of anterior lateral scars and vascula media. Exterior smooth with fine, regular concentric fila. Larval shells of both valves well defined by raised rim, around 0.24 mm wide. Discussion. – Palaeobolus liantuoensis was described from the Lower Cambrian (Shuijingtuo Fm) of South China (Hubei Province) by Zeng (1987). Material assigned to this species was recently described from the Lower Cambrian (Botomian-Toyonian) of Malyi Karatau by Holmer et al. (2001), who also re-figured some topotypes from South China. The new material from Shaanxi is similar to the types of P. liantuoensis in the general outline of the shell, and in having an acuminate ventral valve, with a high triangular pseudointerarea. The Shaanxi shells differ both from the original Chinese material and the Kazakh specimens in having a shorter and less well developed dorsal median septum. The Kazakh specimens also have an ornamentation of concentric rugellae that is lacking in the new material. The maximum size of the shells from Shaanxi is only somewhat less than 2 mm and they most likely represent juveniles. It is possible that the rugellose ornamentation developed later on in the ontogeny.

Genus Kyrshabaktella Koneva, 1986 Type species. – Kyrshabaktella certa Koneva, 1986; Middle Cambrian (Peronopsis? ultimus Biozone); Malyi Karatau, Kazakhstan. Diagnosis. – See Kruse (1990, p. 35).

Fig. 3. A–Q. Palaeobolus liantuoensis Zeng, 1987. All specimens from the lower Shuijingtuo Formation, Zhenba. A–E, M, O from sample SZH-8; F–J, L from sample SZH-9; K, N, P, Q from sample SZH-11. A–B. Ventral valve NIGP135120. A. Exterior, I40. B. Detail of larval shell, I180. C–E. Ventral valve NIGP135121. C. Detail of pseudointerarea, I133. D. Interior, I50. E. Oblique lateral view of interior, I60. F–G. Ventral valve NIGP135122. F. Interior, I50. G. Detail of pseudointerarea, I153. H–J. Dorsal valve NIGP135123. H. Exterior, I60. I. Oblique lateral view of exterior, I50. J. Detail of larval shell, I147. K. Ventral valve exterior NIGP135124, I60. L. Oblique lateral view of dorsal valve interior NIGP135125, I50. M. Ventral valve interior NIGP135126, I40. N. Dorsal valve interior NIGP135127, I60. O. Ventral valve interior NIGP135128, I50. P. Ventral valve exterior NIGP135129, I33. Q. Ventral valve exterior NIGP135130, I60.

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Kyrshabaktella? sp. Figs. 4F–G Material. – 5 fragmentary dorsal valves, from the Xihaoping Member, Xiaoyang section. Remarks. – The dorsal valves of this rare and poorly preserved species form a moderately high, subtriangular high pseudointerarea with a broad, shallow median groove that occupies most of the pseudointerarea. The propareas are very narrow. It is somewhat similar to dorsal valves of Kyrshabaktella davidi described by Ushatinskaya & Holmer (2001, pl. 20, figs. 1–10) from the Lower Cambrian of Australia.

FAMILY EOOBOLIDAE HOLMER, POPOV & WRONA, 1996 Genus Eoobolus Matthew, 1902 Type species. – Obolus (Eoobolus) triparilis Matthew, 1902; Middle Cambrian (Amgian, Bourinot Group), Cape Breton, Canada. Diagnosis. – See Holmer et al. (1996, p. 41).

Eoobolus aff. viridis (Cobbold, 1921) Figs. 6, 7 Synonymy. – • aff. 1921 Lingulella viridis n.sp. – Cobbold, p. 341, pl. 22, figs.10–12. • aff. 1987 Lingulella viridis Cobbold – Hinz, 1987, p. 7, pl. 12, figs. 4, 6, 15. • ? 2001 Eoobolus aff. viridis (Cobbold) – Ushatinskaya & Holmer, p. 123, pl. 16, figs. 10–13, 17, figs. 1–5. Material. – 57 dorsal and 43 ventral valves, all fragmentary, from the Xihaoping Member, Xiaoyang section. Description. – Complete outline of neither valve preserved, apparently somewhat elongate and subtriangular, with maximum width anterior to mid-valve. Ventral valve acuminate, with apical angle around 80–90°. Pseudointerarea close to orthocline, triangular with prominent deep pedicle groove, widening anteriorly. Ventral propareas narrow with well developed flexure lines. Dorsal valve somewhat elliptical in outline, with shallow, broad sulcus. Dorsal pseudointerarea with broad, shallow median depression and narrow propareas with flexure lines poorly developed to absent. Ventral visceral area usually thickened, extending to around midlength. Internal characters variably developed, but usually with V-shaped impression of pedicle nerve bisecting visceral area. Ventral vascula lateralia straight, diverging proximally. Dorsal interior with variably developed visceral area, sometimes strongly thickened with very welldeveloped median septum and tongue, extending to, or anterior to midvalve. Trails of anterocentral muscle scars form distinctive elevated ridges directly lateral to median septum. Larval shell of both valves well defined, around 0.20–0.25 mm across, ornamented by fine circular pits, 0.5–1 mm in diameter. Dorsal larval shell with median sulcus separating two low nodes. Postlarval shell covered by fine concentric growth lines and radiating trails of fine pustules around 5–17 mm across. Discussion. – The specimens from Shaanxi are similar to Eoobolus aff. viridis (Cobbold) from the Lower Cambrian (Parara and Ajax Limestones and Mernmerna Formation) of South Australia (Ushatinskaya & Holmer 2001) in general outline and in having poorly developed flexure lines on the dorsal propareas. However, the ventral apical angle in the Australian species is around 100–110° (compared to 80–90° in the Chinese species) and the ventral pseudointerarea is more widely triangular, with longer propareas as compared with the species from Shaanxi. As noted by Ushatinskaya & Holmer (2001), the poorly known Lingulella viridis Cobbold from the Lower Cambrian (Lower Comley Limestone) of England (Hinz 1987) may be related closely to Eoobolus. The species from Shaanxi appears to differ from all other species in having a larger larval

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Fig. 4. A–E. Palaeobolus liantuoensis Zeng, 1987 from the lower Shuijingtuo Formation, Zhenba; A–C from sample SZH-8; D–E from sample SZH-9. A–B. Ventral valve NIGP135131. A. Exterior, I33. B. Detail of possible predatory boring, I200. C. Dorsal valve exterior NIGP135132, I60. D–E. Dorsal valve NIGP135133. D. Interior, I50. E. Detail of pseudointerarea, I120. F–G. Kyrshabaktella? sp., dorsal valve NIGP135134. F. Detail of pseudointerarea, I80. G. Interior, I40, from the Xihaoping Member, Zhenba, sample SZH-5.

shell and more coarsely developed pustulose ornamentation, with larger pustules. Closer taxonomic discrimination is impossible in view of the fragmented nature of the available specimens.

Eoobolus? shaanxiensis sp. nov. Fig. 8 Holotype. – NIGP135152; Fig. 8E, F. Type locality. – Xiaoyang section, Zhenba, Shaanxi Type horizon. – Dengying Fm. (Xihaoping Mbr.) Derivation of name. – From Shaanxi Province. Material. – 17 dorsal and 21 ventral valves, all fragmentary, from the Xihaoping Member, Xiaoyang section. Diagnosis. – Ventral valve with wide posterior margin and apical angle around 140–170°; pseudointerareas of both valves widely subtriangular with well developed flexure lines; ventral pseudointerarea with deep pedicle groove, widening anteriorly and forming anterior projection along valve floor; dorsal pseudointerarea strongly raised with wide median groove; postlarval ornamentation of radiating trails of fine pustules. Description. – Complete outline of neither valve preserved, but apparently somewhat elongate elliptical. Both valves with faint median sulcus. Ventral valve with wide posterior margin and apical angle around 140– 170°. Ventral pseudointerarea close to orthocline with well-developed flexure lines and prominent deep pedicle groove, widening anteriorly and forming anterior projection along valve floor. Dorsal pseudointerarea apsacline with widely triangular median groove. Dorsal propareas with well developed flexure lines.

Ventral visceral area usually thickened. Internal characters variably developed, but usually with V-shaped impression of pedicle nerve bisecting visceral area and extending to anterior margin of pseudointerarea. Dorsal interior with variably developed visceral area, sometimes thickened with very well developed broad median septum. Larval shell of both valves well defined, apparently smooth, close to circular, around 0.20–0.25 mm across. Dorsal larval shell with median sulcus separating two low nodes. Postlarval shell covered by fine concentric growth lines and radiating trails of fine pustules around 5–15 mm across. Discussion. – The distinctive pustulose ornamentation is only comparable to species belonging to Eoobolus. However, the larval shell does not preserve any traces of pitting, but this could be possibly due to the worn nature of the available valves. Although all available specimens of this species are broken, the combinations of preserved characters are unlike those of any other described species of the Eoobolidae, and it may represent a new genus. The ventral apical angle is wider than that of any previously described species of Eoobolus, and the morphology of the dorsal and ventral pseudointerarea is also quite distinctive, but in view of the unsatisfactory preservation no new genus is established.

FAMILY LINGULELLOTRETIDAE KONEVA & POPOV, 1983 Genus Lingulellotreta Koneva, 1983 (In Gorjansky & Koneva 1983) Type and only species.– Lingulepis malongensis Rong, 1974 (=Lingulellotreta ergalievi Koneva, 1983 (In Gorjansky & Koneva 1983); Wulonqing Mbr, Tsanglangpu Fm. Malong, Yunnan. Diagnosis. – See Holmer et al. (1997, p. 581).

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Fig. 5. Palaeobolus liantuoensis Zeng, 1987. Schematic reconstructions of ventral, A., and dorsal, B. valve interior showing location of measurements.

Lingulellotreta malongensis (Rong, 1974)

Remarks. – Lingulellotreta malongensis is one of the most distinctive Early Cambrian linguloides in Kazakhstan and South China; it is mainly characterized by its elongate foramen, internal pedicle tube, and smooth larval shell, described in detail by Holmer et al. (1997). The material

described by Jin et al. (1993) occurs in the soft-bodied Chengjiang fauna with preserved pedicles. The new specimens isolated from the lower Shuijingtuo Formation at the Xiaoyang section are nearly identical in main morphological characters with the material from Kazakhstan (Shabakty Group, Malyi Karatau) and East Yunnan (Holmer et al. 1997; Jin et al. 1993). However, as compared with the previously recovered specimens, the specimens from the Shaanxi Province are much smaller, with a maximum shell length of 1.6 mm; only about the half size of the specimens from Kazakhstan, and 14 of the specimens from Yunnan. The new Chinese specimens probably represent juveniles. The shells from the Xiaoyang section are exteriorly ornamented with well-developed concentric fila, which are more pronounced as compared with the ornamentation described by Holmer et al. (1997). There is some indication of radial trails of so-called nick-points (see Williams & Holmer 1992, p. 662) between outwardly convex filar drapes, which are probably identical with the more strongly developed “radial costae” described by Jin et al. (1993). The impressions of the vascular trunks in both valves are more strongly impressed as compared with any of the previously described material.

Table 1. Palaeobolus liantuoensis Zeng, average dimensions and ratios of dorsal valves.

Table 2. Palaeobolus liantuoensis Zeng, average dimensions and ratios of ventral valves.

Fig. 9 Synonymy. – • 1974 Lingulepis malongensis n.sp. – Rong, p. 114, pl. 44, figs. 27, 32. • 1993 Lingulepis malongensis Rong – Jin et al., p. 794, figs. 5.1, 5.6, 5.7, 8.1–8.4, 9.4. • 1994 Lingulepis malongensis Rong – Luo et al., pl. 37, figs. 11–14. • 1983 Lingulellotreta ergalievi n.sp. – Koneva (In Gorjansky & Koneva), p. 132, pl. 28, figs. 1–8. • 1997 Lingulellotreta malongensis (Rong) – Holmer et al., p. 581, figs. 4.1– 4.15, 5. • 2001 Lingulellotreta malongensis (Rong) – Holmer et al., p. 56, pl. 13, figs. 11, 13–15. Material. – 13 ventral and 17 dorsal valves, mostly fragmentary, from the lower Shuijingtuo Formation, Xiaoyang section. Diagnosis. – As for genus, by monotypy.

N X S MIN MAX N X S MIN MAX

L

W

H

Il

Iw

Pl

10 1,29 0,408 0,72 1,97

10 1,15 0,374 0,65 1,83

8 0,20 0,097 0,08 0,33

9 0,27 0,102 0,15 0,42

9 0,73 0,285 0,42 1,17

8 0,16 0,057 0,12 0,28

Pw

Vl

L/W

H/L

Il/Iw

Iw/W

Pw/Iw

Vl/L

9 0,29 0,106 0,17 0,42

6 0,87 0,202 0,72 1,25

10 113% 0,081 103% 124%

8 15% 0,026 12% 18%

9 37% 0,028 32% 40%

9 64% 0,061 54% 72%

9 41% 0,064 30% 50%

6 57% 0,047 52% 64%

N X S MIN MAX

L – sagittal length of valves, W – maximum width, H – maximum height of valves, Iw – width of pseudointerarea; Il – length of pseudointerarea, Pw – width of ventral pedicle groove or dorsal median groove, Pl – length of ventral pedicle groove or dorsal median groove, Vl – length of visceral area, Cw – width of cardinal muscle scar, Cl – length of cardinal muscle scar, Sa – length of median septum, X – mean, S – standard deviation, min – minimum observed size, max – maximum observed size, N – number of specimens. All measurements are in millimeters.

N X S MIN MAX

L

W

H

Il

Iw

Pl

10 1,24 0,421 0,67 1,75

10 1,03 0,325 0,53 1,37

3 0,26 0,135 0,10 0,33

10 0,31 0,124 0,15 0,50

10 0,60 0,221 0,30 0,92

10 0,12 0,059 0,03 0,20

Pw

Vl

L/W

H/L

Il/Iw

Iw/W Pw/Iw

Vl/L

10 0,10 0,026 0,07 0,13

6 0,64 0,121 0,50 0,78

10 120% 0,063 109% 128%

3 17% 0,036 13% 20%

10 51% 0,025 47% 56%

10 58% 0,049 51% 67%

6 43% 0,054 34% 50%

10 18% 0,031 15% 23%

Abbreviations as in Table 1. All measurements are in millimeters.

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Fig. 6. A–L. Eoobolus aff. viridis (Cobbold, 1921). All specimens from the Xihaoping Member, Zhenba. A–D, F from sample SZH-5; E, G–L from sample SZH-7. A–B. Ventral valve NIGP135135. A. Exterior, I30. B. Detail of larval shell, I60. C–D. Dorsal valve NIGP135136. C. Detail of pustulose ornamentation, I300. D. Exterior, I50. E. Dorsal valve interior NIGP135137, I40. F. Ventral valve interior NIGP135138, I40. G–H. Dorsal valve NIGP135139. G. Detail of possible predatory boring, I400. H. Exterior, I50. I–J. Dorsal valve NIGP135140. I. Exterior, I50. J. Detail of larval shell, I200. K–L. Ventral valve NIGP135141. K. Interior, I40. L. Detail of broken shell showing laminar succession, I600.

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Fig. 7. A–K. Eoobolus aff. viridis (Cobbold, 1921). All specimens from the Xihaoping Member, Zhenba. A, D from sample SZH-3; B–C, E from sample SZH-5; F–K from sample SZH-7. A. Dorsal valve exterior NIGP135142, I40. B–C. Dorsal valve NIGP135143. B. Exterior, I24. C. Detail of pustulose ornamentation, I120. D. Dorsal valve interior NIGP135144, I33. E. Dorsal valve interior NIGP135145, I33. F–G. Ventral valve NIGP135146. F. Interior, I40. G. Detail of pseudointerarea, I153. H–I. Ventral valve NIGP135147. H. Exterior, I30. I. Detail of pustulose ornamentation, I300. J–K. Ventral valve NIGP135148. J. Exterior, I30. K. Detail of pitted larval shell, I2000.

202


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Fig. 8. A–I. Eoobolus? shaanxiensis sp. nov. All specimens from the Xihaoping Member, Zhenba. A, C–D from sample SZH-5; B, E–I from sample SZH-7. A. Dorsal valve exterior NIGP135149, I40. B. Dorsal valve interior NIGP135150, I40. C–D. Ventral valve NIGP135151. C. Interior, I33. D. Detail of pseudointerarea, I67. E–F. Holotype, ventral valve NIGP135152. E. Interior, I33. F. Exterior, I30. G–H. Dorsal valve NIGP135153. G. Exterior, I40. H. Detail of larval shell, I180. I. Dorsal valve exterior NIGP135154, I30.

Fig. 9. A–N. Lingulellotreta malongensis (Rong). All specimens from the lower Shuijingtuo Formation, Zhenba. G–H, M–N from sample SZH-8; A–F, I–L from sample SZH-10. A–F. Ventral valve NIGP135155. A. Detail of exterior, I100. B. Exterior, I40. C. Oblique lateral view of exterior, I47. D. Oblique posterior view of larval shell, I167. E. Detail of pseudointerarea, I147. F. Interior, I40. G–H. Dorsal valve (specimen lost during SEM). G. Interior, I33. H. Detail of pseudointerarea, I100. I–J. Dorsal valve NIGP135156. I. Interior, I50. J. Oblique lateral view of interior, I60. K. Ventral valve interior NIGP135157, I50. L. Dorsal valve exterior NIGP135158, I40. M–N. Dorsal valve NIGP135159. M. Exterior, I60. N. Oblique posterior view of larval shell, I220.

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204


SUPERFAMILY ACROTHELOIDEA WALCOTT & SCHUCHERT, 1908 (IN WALCOTT, 1908) FAMILY BOTSFORDIIDAE SCHINDEWOLF, 1955 SUBFAMILY BOTSFORDIIDAE SCHINDEWOLF, 1955 Genus Botsfordia Matthew, 1891 Type species. – Obolus pulcher Matthew, 1899; upper Lower Cambrian (Hanford Brook Formation), New Brunswick, Canada.

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lingulide musculature and ontogeny. Popov (1992, fig. 3) proposed a model for understanding and reconstructing the acrotretid musculature, in which the conical ventral valve may be viewed as a lingulid ventral valve that is ”rolled up” along the posterior margin. The acrotretid pedicle foramen would have been formed by the closure of the lingulid pedicle groove. Moreover, in attaining a conical shape, the complex lingulid musculature would have been simplified and the acrotretid apical process is then simply a modified lingulid muscle platform. The ontogeny of Eohadrotreta, where the ventral valve retains an unrestricted and open botsfordiid-like delthyrium through much of the ontogeny, gives support to this view.

Diagnosis. – See Holmer et al. (2001, p. 66).

Botsfordia minuta sp. nov. Fig. 10

SUPERFAMILY ACROTRETOIDEA SCHUCHERT, 1893 FAMILY ACROTRETIDAE SCHUCHERT, 1893

Holotype. – NIGP135162, complete shell; Fig. 10D–H. (W = 0.88 mm, L = 0.65 mm)

Genus Eohadrotreta gen. nov.

Type locality. – Xiaoyang section in Zhenba, Shaanxi

Type species. – Eohadrotreta zhenbaensis gen. et sp. nov.

Type horizon. – Lower Cambrian Shuijingtuo Formation

Derivation of name. – Latin, Eo, early; an early form similar to Hadrotreta.

Derivation of name. – Latin minutus, referring to the small size of the larval apical tubercles. Material. – 7 complete juvenile shells, from the lower Shuijingtuo Formation, Xiaoyang section. Diagnosis. – Shell almost equivalved, only slightly ventribiconvex. Ventral larval shell with vestigial central median apical tubercle. Ventral pseudointerarea not clearly differentiated. Dorsal larval shell with two vestigial apical tubercles. Postlarval shell with evenly distributed fine pustules. Description. – Shell almost equivalved, only very slightly ventribiconvex, subcircular to transversely oval in outline, 110–140% as wide as long. Ventral valve very gently convex in lateral view with maximum width immediately posterior to midvalve. Ventral beak slightly acuminate, extending somewhat beyond posterior margin and forming minute triangular delthyrium. Ventral pseudointerarea not clearly differentiated. Dorsal valve flattened in lateral view. Interior of both valves unknown. Larval shell of both valves well defined by raised rim, transversely oval, around 0.40–0.45 mm wide, and 150% as wide as long. Ventral larval shell with vestigial central median apical tubercle. Dorsal larval shell with two vestigial apical tubercles. Postlarval shell ornamented by regularly distributed low pustules, 5–7 µm across, and increasing in size anteriorly. Discussion. – It is possible that the available specimens all represent juveniles, and the recorded maximum shell width is only 0.9 mm. The new species differs from other species of Botsfordia in; 1) the larval shells of both valves have only vestigial apical tubercle-like structures, whereas those of most typical species of Botsfordia are well-developed and high, 2) The delthyrium is extremely small and lacks a well defined pseudointerarea, and 3) the ventral beak is only somewhat acuminate. The pustulose ornamentation is not well known from most other described species of Botsfordia due to poor preservation.

ORDER ACROTRETIDA KUHN, 1949 Origin and phylogenetic position. – The origin and phylogenetic position of the Acrotretida is still poorly known. The cladistic analyses by Holmer & Popov (1996, 2000) support the view that the order is a potentially monophyletic group. However, the phylogenetic relationship between the Acrotretida and the rest of the Lingulata is still very uncertain (see also Holmer 2001; Holmer et al. 2002). As noted by Holmer (1989), Popov (1992), and Holmer & Popov (2000), it has been assumed that the acrotretid muscle system and ontogeny are derived in relation to the

Diagnosis. – Shell subcircular to transversely oval with rounded to straightened posterior margin. Ventral valve widely conical to gently convex. Ventral pseudointerarea gently procline with shallow to vestigial intertrough. Foramen not enclosed within larval shell, remaining open through much of ontogeny. Apical process and apical pits vestigial to absent. Dorsal valve gently convex. Dorsal pseudointerarea narrowly triangular, orthocline with median groove. Dorsal median buttress welldeveloped. Dorsal median septum well-developed, extending anterior to midvalve. Discussion. – The new genus mainly differs from Hadrotreta Rowell, 1966 in that the interior of the ventral valve lacks a well-developed apical process and apical pits, and the dorsal valve is not sulcate. Eohadrotreta is also somewhat similar to Aphelotreta Rowell, 1980, which also lacks both apical process and apical pits. However, it can be distinguished from Aphelotreta by having a broadly conical ventral valve with a procline pseudointerarea, as well as having a well-developed median septum, extending anterior to the midvalve. The ventral valve of Aphelotreta is strongly convex and apsacline and the dorsal median septum is poorly developed. The new genus is also somewhat similar to Curticia Walcott, 1905 in that it has a triangular delthyrium through some of its ontogeny. However, the delthyrium in Curticia is produced through subsequent resorption of shell material and there are no signs of resorption in the Shaanxi material.

Eohadrotreta zhenbaensis gen. et sp. nov. Figs. 11–13, Tables 3, 4 Holotype. – NIGP135165, ventral valve; Fig.11A, B. Type locality. – Xiaoyang section, in Zhenba, South Shaanxi Type horizon. – Lower Cambrian, lower Shuijingtuo Formation Derivation of name. – After its occurrence in Zhenba county. Material. – 6 complete juvenile shells, 32 ventral and 21 dorsal valves, from the lower Shuijingtuo Formation, Xiaoyang section. Diagnosis. – Ventral valve widely conical. Ventral pseudointerarea procline with shallow intertrough. Dorsal valve gently convex. Dorsal median septum low. Description. – Shell ventribiconvex, subcircular to transversely oval, with straightened posterior margin. Ventral valve on average 84% as long as wide, with maximum width near midvalve. Ventral valve widely conical,

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205

Fig.10. A–M. Botsfordia minuta sp. nov. All specimens from sample SZH-8, the lower Shuijingtuo Formation, Zhenba. A. Dorsal view of complete shell NIGP135160, I80. B–C. Complete shell NIGP135161. B. Dorsal view, I80. C. Oblique posterior view of dorsal valve, I80. D–H. Holotype, complete shell NIGP135162. D. Ventral view, I80. E. Lateral view of ventral exterior, I93. F. Oblique posterior view of ventral exterior, I60. G. Detail of pustulose ornamentation, I600. H. Detail of ventral larval shell, I133. I–L. Complete shell NIGP135163. I. Ventral view, I80. J. Detail of pitted ventral larval shell, I3000. K. Detail of pustulose post-larval ornamentation, I400. L. Detail of ventral larval shell, I153. M. Ventral view of complete shell NIGP135164, I60.

206


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207

Fig.12. A–F. Eohadrotreta zhenbaensis gen et sp. nov. All specimens from the lower Shuijingtuo Formation, Zhenba. A, D from sample SZH-8; B– C, E from SZH-10. A. Ventral valve interior NIGP135173, I60. B–C. Ventral valve NIGP135174. B. Oblique anterior view of interior, I80. C. Oblique posterior view of unrestricted delthyrium, I400. D. Dorsal posterior view of complete shell NIGP135175, I100. E–F. Dorsal valve NIGP135176. E. Oblique posterior view, I93. F. Oblique posterior view of larval shell, I233.

on average 40% as high as long, with maximum height in posterior half of valve. Ventral pseudointerarea procline to almost catacline, divided by broad, shallow intertrough. Pedicle foramen elongate oval, on average 0.07 mm wide and 0.10 mm long. Pedicle foramen not enclosed within larval shell, remaining open through early ontogeny until shell reaches around 0.5–0.7 mm in width. Ventral interior lacking well defined apical process and apical pits. Some specimens with poorly impressed and short vascula lateralia. Dorsal valve on average 89% as long as wide. Dorsal valve gently convex, on average 24% as long as high. Dorsal pseudointerarea short and orthocline, on average 12% as long as wide and occupying 44% of shell width. Median groove broad, shallow, occupying on average 75% of width of pseudointerarea. Dorsal median septum distinct, on average extending for 51% of shell length. Median buttress well developed. Dorsal cardinal muscle scars usually well defined, occupying on average

Fig. 11. A–N. Eohadrotreta zhenbaensis gen et sp. nov. All specimens from the lower Shuijingtuo Formation, Zhenba. A–B, M–N from sample SZH-8; C–E, K–L from sample SZH-10; F–J from sample SZH-11. A–B. Holotype, ventral valve NIGP135165. A. Exterior, I40. B. Oblique posterior view, I40. C–D. Ventral valve NIGP135166. C. Exterior, I60. D. Detail of larval shell and pedicle foramen, I200. E. Dorsal valve exterior NIGP135167, I47. F–H. Ventral valve NIGP135168. F. Exterior, I60. G. Oblique posterior view of larval shell and pedicle foramen, I167. H. Detail of pitted larval shell, I2000. I–J. Dorsal valve NIGP135169. I. Interior, I60. J. Oblique lateral view of interior, I87. K–L. Dorsal valve NIGP135170. K. Oblique lateral view of interior, I80. L. Interior, I50. M. Dorsal valve exterior NIGP135171, I60. N. Ventral valve exterior NIGP135172, I67.

59% of shell width and extending for 29% of shell length. Some specimens with elongate impressions of anterocentral muscle scars directly lateral to anterior end of median septum.

Table 3. Eohadrotreta zhenbaensis gen. et sp. nov., average dimensions and ratios of dorsal valves. L N 11 X 0,58 S 0,231 MIN 0,38 MAX 1,17 L/W N 11 X 89% S 0,115 MIN 76% MAX 121%

W

H

Il

Iw

Pw

Cl

11 0,67 0,288 0,32 1,33

10 0,14 0,059 0,07 0,25

10 0,04 0,023 0,02 0,08

10 0,32 0,140 0,18 0,58

10 0,23 0,083 0,15 0,42

6 0,21 0,092 0,10 0,37

6 9 0,49 0,32 0,182 0,144 0,30 0,18 0,75 0,67

H/L

Il/Iw

Iw/W Pw/Iw

Cl/L

Cw/W

Sa/L

10 24% 0,048 17% 32%

10 12% 0,031 8% 17%

10 44% 0,047 38% 52%

6 29% 0,038 23% 34%

6 59% 0,058 53% 70%

9 51% 0,054 44% 60%

10 75% 0,180 52% 100%

Cw


Table 4. Eohadrotreta zhenbaensis gen. et sp. nov., average dimensions and ratios of ventral valves. N X S MIN MAX

L

W

H

L/W

H/L

9 0,64 0,226 0,32 0,97

9 0,76 0,261 0,38 1,12

8 0,25 0,117 0,10 0,42

9 84% 0,030 81% 90%

8 40% 0,072 30% 48%


Sa

208


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Fig. 13. Eohadrotreta zhenbaensis gen et sp. nov. Schematic reconstructions of ventral exterior, A. and dorsal valve interior, B. showing location of measurements.

Eohadrotreta zhujiahensis gen. et sp. nov. Dorsal valve gently convex, on average 19% as long as high. Dorsal pseudointerarea short and orthocline, occupying less than half of shell width. Median groove broad, shallow. Dorsal median septum distinct, extending for more than half of shell length, and bifurcating anteriorly. Median buttress well developed. Dorsal cardinal muscle scars usually well defined, occupying more than half of shell width.

Figs. 14–15, Table 5 Holotype. – NIGP135177, Fig. 14A–E, nearly complete shell. Type locality. – Fucheng section, south Shaanxi Type horizon. – Lower Cambrian, Guojiaba Formation. Derivation of name. – After the Zhujiahe river at the Fucheng section. Material. – 53 complete juvenile shells, 8 ventral and 11 dorsal incomplete valves, from the Guojiaba and Xiannüdong Formations, Fucheng section. Diagnosis. – Ventral valve gently convex. Ventral pseudointerarea short and procline, with vestigial intertrough. Foramen remaining open through most of ontogeny. Dorsal median septum extending anterior to midvalve, bifurcating anteriorly. Description. – Shell only slightly ventribiconvex, subcircular to transverse oval with convex posterior margin, on average 92% as long as wide. Ventral valve with maximum width near midvalve, moderately convex, on average 27% as high as long, with maximum height in posterior half of valve. Ventral pseudointerarea procline with indistinct intertrough. Pedicle foramen elongate oval, on average 0.09 mm wide and 0.11 mm long. Pedicle foramen not enclosed within larval shell, remaining open through most of ontogeny until shell reaches around 0.7–0.9 mm in width. Ventral interior lacking well defined apical process and apical pits. Some specimens with poorly impressed and short vascula lateralia.

Table 5. Eohadrotreta zhujiahensis gen. et sp. nov., average dimensions and ratios of complete shells. N X S MIN MAX

L

W

Hd

Hv

L/W

Hd/L

Hv/L

13 0,70 0,195 0,40 1,05

13 0,77 0,244 0,42 1,25

13 0,13 0,042 0,07 0,23

13 0,19 0,073 0,10 0,37

13 92% 0,063 80% 104%

13 19% 0,020 16% 23%

13 27% 0,039 20% 35%


Discussion. – The outline and the size of the new species are somewhat similar to E. zhenbaensis described above, but E. zhujiahensis differs from it in that the foramen is closed at an even later ontogenetic stage, and the ventral valve is less conical and has a vestigial intertrough. The pedicle foramen of the poorly known species, Curticia minuta Bell, from the Lower Cambrian of England (Hinz 1987), appears to show some similarities with Eohadrotreta zhujiahensis, but this needs to be confirmed from better material of the English species. Acknowledgments. – We thank Junming Zhang for assistance in the field, and Yongqiang Mao for SEM microphotography. This work was supported by research grants from the National Natural Science Foundation of China, the National Ministry of Science and Technology of China (Grant Number G2000077700), and the Chinese Academy of Sciences. Lars E. Holmer´s work was supported by grants from the Swedish Natural Sciences Research Council (VR). L.R.M Cocks reviewed the manuscript and offered suggestions that improved the final submission.

Fig. 14. A–O. Eohadrotreta zhujiahensis gen et sp. nov. All specimens from the Fucheng section, Nanzheng. A–E, M–O from sample SF-1, F– L from sample SF-2. A–E. Holotype, complete shell NIGP135177. A. Ventral exterior, I60. B. Oblique postero-lateral view, I67. C. Oblique posterior view, showing unrestricted delthyrium, I60. D. Detail of larval pitting of dorsal larval shell, I3000. E. Detail of dorsal larval shell, I300. F–G. Complete shell NIGP135178. F. Oblique posterior view, I60. G. Dorsal view, I60. H. Lateral view of ventral valve interior NIGP135179, I100. I–J. Complete shell NIGP135180. I. Ventral view, I100. J. Oblique posterior view, I100. K–L. Dorsal valve NIGP135181. K. Oblique interior view, I60. L. Interior, I67. M. Dorsal valve interior NIGP135182, I60. N–O. Complete shell NIGP135183. N. Oblique postero-lateral view, I100. O. Ventral view, I80.

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209

210


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211

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Fig. 15. A–N. Eohadrotreta zhujiahensis gen et sp. nov. All specimens from the Fucheng section, Nanzheng. B–G from sample SF-1; A, H–N from sample SF-2. A. Dorsal valve interior NIGP135184, I60. B–D. Complete shell NIGP135185. B. Detail of ventral larval shell, I180. C. Ventral view, I67. D. Oblique postero-ventral view, I80. E–F. Complete shell NIGP135186. E. Ventral view, I80. F. Oblique postero-ventral view, I80. G. Dorsal valve interior NIGP135187, I60. H. Ventral valve interior NIGP135188, I60. I–J. Complete shell NIGP135189. I. Dorsal view, I80. J. Detail of pitted dorsal larval shell, I2000. K–L. Complete shell NIGP135190. K. Dorsal view, I80. L. Oblique posterior view, I80. M–N. Ventral valve NIGP135191. M. Oblique anterior view of interior, I80. N. Detail of columnar microstructure, I500.

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