Lingulata, Brachiopoda) from Southern China Zhifei Zhang,1 Jian Han,1 Xingliang Zhang,1 Jianni Liu1, Junfeng Guo1 and Degan Shu1,2

中国科技论文在线 http://www.paper.edu.cn Acta Zoologica (Stockholm) 88: 65–70 (January 2007)

NoteBlackwell Publishing Ltd on the gut preserved in the Lower Cambrian Lingulellotreta (Lingulata, Brachiopoda) from southern China Zhifei Zhang,1 Jian Han,1 Xingliang Zhang,1 Jianni Liu1, Junfeng Guo1 and Degan Shu1,2

Abstract 1Department of Geology and Early Life Zhang Z., Han J., Zhang X., Liu J., Guo J. and Shu D. 2007. Note on the gut Institute, State Key Laboratory for preserved in the Lower Cambrian Lingulellotreta (Lingulata, Brachiopoda) Continental Dynamics, Northwest from southern China. — Acta Zoologica (Stockholm) 88: 65–70 University, Xi’an, 710069, China; 2School of Earth Sciences and Rescources, Lingulellotreta malongensis Rong is the earliest known taxon of the family China University of Geosciences, Beijing, Lingulellotretidae, which is characterized by the presence of a pedicle foramen 100083, China as well as an internal pedicle tube. New material from the Early Cambrian Chengjiang Lagerstätte of southern China provides improved anatomical Keywords knowledge for lingulellotretid species especially for the digestive system. linguloidea, Brachiopoda, digestive tract, Early Cambrian, Chengjiang Lagerstätte Additional gut fossils exhibit distinctly the anterior portion composed of esophagus and distended stomach, situated in the alleged visceral cavity, with Accepted for publication: the recurved intestine accommodated inside a hollow pseudointerarea. 2 August 2006 The frequency of occurrence of this intestinal layout suggests that this is not just an artefact of preservation. The gross conﬁguration of the guts and the way they are preserved in the fossils suggest that they are in situ and, therefore, we can assume that Lingulellotreta had a hollow cavity presumably subtended by the pseuodelthyrium, which was invaded and occupied by the visceral organs. Hence, these fossils demonstrate the dangers of extrapolating crown-group soft-tissue conﬁguration to the stem group. Z. F. Zhang, Early Life Institute and Department of Geology, Northwest University, Xi’an, 710069, China. E-mail: [email protected] or [email protected]

Yunnan Province, southern China, which has surpassed the Introduction classic Burgess Shale for yielding important information on The Lingulata was originally established by Gorjansky several key steps in early deuterostome evolution (e.g. Shu and Popov (1985, 1986) as a separate class clade outside the et al. 2003, 2004, and references therein), as well as in the Brachiopoda. However, it is now commonly regarded as a preservation of nonmineralized internal tissues of known monophyletic group within the Brachiopoda (Holmer 1989; brachiopod taxa (Zhang et al. 2003, 2004a,b, 2005, 2006; Popov et al. 1993; Carlson 1995; Holmer et al. 1995; Cohen Holmer and Caron 2006). In this deposit, the family Lin- et al. 1998). The class then comprised three orders: Lingulida, gulellotretidae is represented by the numerically dominant Acrotretida and Siphontretida. In the revised Treatise on brachiopod Lingulellotreta malongensis Rong, 1974, which is Invertebrate Palaeontology (Part H) (Holmer and Popov the earliest known taxon of the family, and which is unique 2000), the concept of the Lingulida was expanded to encom- within the Linguloidea in having an elongate pedicle foramen pass the three superfamilies Linguloidea, Discinoidea and and an internal pedicle tube (Holmer et al. 1997). Details of Acrotheloidea. Of these, the ﬁrst two are the only extant the morphology of the lingulellotretid species have been organophosphatic-shelled stocks, and thus have unquestion- made available (Jin et al. 1993; Holmer et al. 1997; Zhang able living representatives. They share many characters, et al. 2004a,b, 2005), including the pedicle, musculature, including type of musculature, pedicle, digestive tract, mantle mantle canal system, as well as the organization of the lopho- canal system, ontogeny, and shell structure. The majority of phore and the digestive system (Zhang et al. 2004a,b, 2005). these characters can also be traced back to their fossil repre- In this paper, we illustrate additional specimens from the sentatives (Steel-Petrovic 1976). Fossil lingulids are abundant Chengjiang Lagerstätte showing preservation of a U-shaped in the celebrated Early Cambrian Chengjiang Lagerstätte in digestive tract. The additional well-preserved material of

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Note on the Lower Cambrian lingulid gut • Zhang et al. Acta Zoologica (Stockholm) 88: 65–70 (January 2007)

Lingulellotreta allows a further account given here of the dictated by the activities of bacteria during early diagenesis, disposition of the alimentary canal inside the shells. which most likely varied in category of organism, colonizing either on or inside the tissue masses. However, this proposal remains to be resolved. Anyway, the three-dimensional ali- Preservation mentary canals suggest that the early diagenetic mineraliza- The strata containing the Chengjiang fossils come from the tion of some Chengjiang animals most likely took place prior Yu’anshan Member (Eoredlichia Zone), i.e. the upper part of to the breakdown of their nonmineralized carcasses. the Early Cambrian Heilinpu (formerly Qiongzhusi) Forma- tion, exposed in a wide area around Kunming, Yunnan, New fossil evidence China (Luo et al. 1999). The fossils in our collection are reddish-brown or yellowish-green after weathering, and The U-shaped arrangement of the digestive canal in Lingule- embedded in greyish-green and greyish-yellow mudstone llotreta malongensis has been confirmed by fossils from the intercalated with greyish-brown siltstone. The mudstone is Lower Cambrian of southern China (Zhang et al. 2004a). fine-grained enough for the details of the fossils to be pre- Based on analogy with extant species, the digestive tract served with remarkable fidelity. However, differential weath- should unquestionably be accommodated inside the visceral ering played an essential role in the final appearance of the cavity. Nevertheless, close examination of many more macroscopic Chengjiang fossils in that the fresh mudstone superbly well-preserved informative specimens (Fig. 1) from the strata is dark grey and that contrasts little with the urges us to cast doubt on this ubiquitous argument. As seen contained fossils, which make it difficult to differentiate a in Fig. 1(A), the alimentary canal is represented by a narrow, fossil from the surrounding matrix. However, a fossil, when partially mud-filled three-dimensional tube-like structure deeply weathered, appears as a variable degree of reddish- (Fig. 2A). It arises at the base of the less intricately spiral brown to yellowish-brown, with a striking colour contrast to lophophore, extends posteriorly as an approximately 0.5- to the surrounding greyish-green to greyish-yellow rock. 1-mm-long oesophagus leading into a pouch-like stomach The new specimens of Lingulellotreta examined here are all (Fig. 2A,B). Beyond the stomach, the digestive canal con- dorsoventrally compressed, and preserved parallel to the tinues as a narrow intestine filled with muddy sediment. bedding plane. Their shells are flattened into a thin film so Extending posteriorly approximately 0.8 mm away from the that the two valves are indistinguishable from each other. The stomach, the intestine markedly passes through the hinge line digestive tract of Lingulellotreta malongensis occurs either as a into the pseudointerarea, and continues as an approximately darkish thread-like line or partly or completely mud-filled 1.2-mm mud-filled tube (Fig. 2A,B). Then, it recurves and tubes with considerable relief (also see Zhang et al. 2004a). instead extends forwards close to the extremity of hinge line, However, the ingestion of sediment is an unlikely explana- finally terminating in an anal opening on the right anterior tion for the three-dimensional preservation of the alimentary body wall (Fig. 1A–C). canals in the Chengjiang lingulids. This is because brachio- In specimen ELI L-0060, composed of part and counter- pods are suspension filter-feeders. Thus, it would be difficult part, the digestive tract is a distinct darkish-brown recurved to explain the presence of a large amount of mud ingested in line (Fig. 1D,E). With respect of the disposition, this struc- their gut (Zhang et al. 2005). The preservation of soft tissues ture coincides well with the gut seen in Fig. 1(A–C), both indicates that these specimens represent complete carcasses invading and occupying the hollow cone-shaped interspace rather than shell valves. Although the exceptional preserva- presumably being subtended by the pseuodelthyrium, delin- tion of the Chengjiang fauna has attracted considerable eated by a triangular lineation in the fossils (Fig. 2). The attention, efforts have been focused on the various processes upward recurved portion of the intestine can be preserved in that triggered the preservation of the soft-bodied organisms many specimens (Fig. 1) (also see Zhang et al. 2004a, Fig. 1F). (Babcock et al. 2001; Zhu et al. 2001, 2005; Gabbott et al. Twenty fossils were available for the study presented here; all 2004). The underlying mechanisms for the fossilization of are deposited in the Early Life Institute (prefix ELI) and the soft tissues and hard skeletons remain obscure. Intriguingly, Department of Geology, Northwest University, Xian, China. both the slightly mineralized shells and the nonmineralized labile organic tissues can be preserved as reddish-brown Implications and discussion films. In addition, the quality and mode of preservation of identical tissues of an organism varies considerably in different The unusual disposition of the alimentary canal of Lingulel- specimens. Diagenetic mineralization, notably pyritization, lotreta malongensis beyond the hinge line into the pseudointer- assuredly played a key role in the exceptional preservation of area is indeed bewildering. One possible explanation for the the nonmineralizing tissues of animals from the Chengjiang configuration is that this posterior portion of the digestive deposit (Gabbott et al. 2004; Zhu et al. 2005). Crucial in this canal was forced out of the posterior body wall when the respect is how to interpret the origin of the authigenic organism was rapidly buried alive, accompanied by strong minerals as pseudomorphs for the different organic tissues, compression. Arguing against this proposal is the fact that the which were replicated with fidelity. The origin was presumably integuments were not crushed or strongly distorted posteriorly.

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Acta Zoologica (Stockholm) 88: 65–70 (January 2007) Zhang et al. • Note on the Lower Cambrian lingulid gut

Fig. 1—The aberrant digestive tract (single arrows) of Lingulellotreta malongensis from the Yu’anshan Member of the Heilinpu (formerly Qiongzhusi) Formation, Lower Cambrian, southern China. —A–C. showing the three-dimensional tube-like digestive canals. —A. ELI L- 0413, a dorsoventrally flattened specimen with lophophore imprints. —B. ELI L-0091B, a parallel flattened internal mold with lophophore. —C. Close-up view of the alimentary canal in specimen ELI L-0091A; note the location of hinge line (tailed arrow). —D–E. ELI L-0060A,B, showing the U-shaped digestive tract of L. malongensis preserved as linear impressions. —F. ELI L-0061, a strongly compressed specimen showing a partially mud-filled tube-like intestine. Scale bars 2 mm. See Fig. 2 for some interpretations.

If burial pressure ruptured the body cavity, one would expect conﬁguration. In addition, the frequency of occurrence of that the anterior body wall would also commonly fail. More- this type of preservation of the digestive tracts in the fossil over, even given failure, it seems improbable that the guts of state in association with complete shells suggests that this is the body cavity would be extruded regularly as a U-shaped not an artefact of preservation. The U-shaped conﬁguration of

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Note on the Lower Cambrian lingulid gut • Zhang et al. Acta Zoologica (Stockholm) 88: 65–70 (January 2007)

Fig. 2—Interpretative drawings of the specimens of Lingulellotreta malongensis shown in Fig. 1. —A. Sketch of Fig. 1(A) —B. Sketch of Fig. 1(B). —C. Sketch of Fig. 1(D). Abbreviations: Ao, anal opening; Bc, body cavity; Es, oesophagus; Hl, hinge line; Lo, lophophore; Ri, recurved intestine; So, shell of other organism; St, stomach.

Fig. 3—Morphological comparison of Lingulellotreta malongensis between specimens from Chengjiang (Heilinpu Formation) and Canglangpu Formation (Wulongqing Member), Yunnan. Scale bars 2 mm. —A. ELI L-0185A, a ﬂattened composite mould derived from the Chengjiang deposit; note the elongate pseudointerarea with a hollow triangular region (single arrow). —B–D. Specimens from the Lower Cambrian Canglangpu Formation, Wulongqing Member, overlying the Heilinpu formation. —B–C. A composite mold; note the shell ornamentation and pseudointerarea. —D. A compressed dorsal valve with the proximate part of pedicle (tailed arrow).

the mud-infillings and the way they arise from the base of through which the coelomic fluid was admitted into the the lophophore suggest unambiguously that they are in situ coelomic cavity in the pedicle. The three-dimensional alimentary canals. pseudointerareal cavity is quite distinct in the acid-etched The existence of a recurved gut posterior to the hinge line specimens of the lingulellotretid species from the Shuijingtuo implies that there was a funnel-like hollow cavity presumably Formation of southern Shaanxi Province, southern China (Li subtended by the pseuodelthyrium, which was delineated by and Holmer 2004), and from Kazakhstan (Shabakty Group, a triangular darkish line (Fig. 3A) (see also Zhang et al. 2004a, Malyi Karatau) (Holmer et al. 1997). The material from the figs 1 and 2). The cavity could accommodate the visceral two regions bears a general resemblance to each other but organs, for example, plus the posterior part of the digestive has a clear difference in size. The southern Shaanxi specimen tract and the umbonal muscles. This atypical disposition of is only about half the size of the specimens from Kazakhstan intestine in fossils is outside the morphological and functional but at least one quarter the size of the specimens from the range found in extant lingulid forms. It corroborates the Chengjiang deposits (Li and Holmer 2004). The Chengjiang dangers of extrapolating crown-group soft-tissue morphology specimens were commonly thought to resemble those recov- to the stem-group as emphasized by Sutton et al. (2005). ered from the Wulongqing Member (recently Wulongqing Beyond the cavity subtended by the pseudointerarea of Formation) of the Canglangpu (formerly Tsanglangpu) For- Lingulellotreta malongensis was the internal pedicle tube, mation, where the type specimen was found in the Siqitian

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Acta Zoologica (Stockholm) 88: 65–70 (January 2007) Zhang et al. • Note on the Lower Cambrian lingulid gut

Chengjiang, with that of Lingulellotreta from the Canglangpu deposits argues for a gradual reduction of the pseudointerarea during lingulellotretid brachiopod macroevolution, and accordingly an extension forward of the posterior wall. An elongated pseudointerarea is therefore presumed to have been a disadvantage with might have caused their extinction by the end of the Middle Cambrian. The Lingulata was originally established by Gorjansky and Popov (1985, 1986) as a separate class clade outside the Brachiopoda. However, it is now commonly regarded as a monophyletic group within the Brachiopoda (Holmer 1989; Popov et al. 1993; Carlson 1995; Holmer et al. 1995; Cohen et al. 1998). The class then comprised three orders: Lingulida, Acrotretida and Siphontretida. In the revised Treatise on Invertebrate Palaeontology (Part H) (Holmer and Popov 2000), the concept of the Lingulida was expanded to encom- pass the three superfamilies Linguloidea, Discinoidea and Acrotheloidea. So far, there are at least four genera of linguloid brachiopods from the Chengjiang fauna including obolids Fig. 4—An undescribed soft-shelled lingulid brachiopod from and lingulotretids, in which a horizontally curved U-shaped the Chengjiang Lagerstätte, south China, showing the elongate digestive tract with an anterior anus has been observed triangular ventral pseudointerarea filled with sediment grains. (Zhang et al. 2004a, 2005, 2006). The occurrence of this —A. ELI W-0200, note the compressed wrinkles (white arrow) on type of gut layout in the fossil state thus lends an essential the pseudointerareal margin and pedicle impression (double arrow) support for the monophyly of the superfamily Linguloidea. with a coelomic lumen (tailed arrow). —B. ELI W-0018A, an In addition, Lingulellotreta malongensis is the earliest known internal natural mold. taxon of the family Lingulellotretidae, which is characterized by the presence of a pedicle foramen as well an internal pedicle section, Malong, Yunnan (Rong 1974; Holmer et al. 1997). tube. The foramen bears some general resemblance to those The Canglangpu siltstone has generally thought to have been occurred in acrotretids and siphonotretids. It is plausible to deposited during the Botomian stage of the Lower Cambrian presume that the acrotretids and siphonotretids might have (Luo et al. 1994, 1999). However, detailed description of the been derived from Wangyuia-like stem group of linguloideans specimens embedded in the Canglangpu deposits remains to with an elongate hollow pseudointerarea. be done. Some specimens recently excavated from Cang- laangpuian strata near Qiongzhusi temple situated in the Xishan Acknowledgements district of Kunming (see Holmer et al. 1997, Fig. 3) exhibit some distinct features, notably the relatively shorter pseudo- Our work is financed by the National Natural Science Foun- interarea to shell length, the ratio of length to width of the dation of China (grant 40332016) and the Program for ventral valve, and the distinct surface ornamentation (Fig. 3). Changjiang Scholars and Innovative Research Team in the Nevertheless, a detailed comparison of the specimens from University (PCSIRT). The first author (Z. Zhang) owes the Chengjiang (Atdabanian) and Canglangpu deposits of thanks to Professor Lars Holmer for advice. We also thank the Lower Cambrian of Yunnan, China, is somewhat beyond Drs G. X. Li (Nanjing) for advice; S. X. Hu (Kunming) for the scope of this paper and thus remains to be resolved. some technical assistance in the field; H. X. Guo and Y. C. Yao The elongate hollow pseudointerarea of the lingulid speci- for help with field work; and J. P. Zhai and M. R. Cheng for mens examined herein is reminiscent of that which occurs in preparation of the fossils. Many thanks are due to Dr Susan the possible soft-shelled brachiopod Wangyuia chengjiangensis Turner (Queensland Museum) for English improvement, Jin et al., 2004, from the Chengjiang mudstone deposits and to two anonymous referees for their valuable comments (Fig. 4). The interior of the latter contains substantial agglu- that greatly improved the manuscript. tinated detrital grains (Fig. 4A,B), contrasting strikingly with the compressed wrinkled marginal wall of the pseudo- References interarea, suggesting its interior was approximately an elliptically funnel-shaped cavity. The maximum length of the Babcock, L. E., Zhang, W. T. and Leslie, S. A. 2001. The Chengjiang biota: record of the Early Cambrian diversification of pseudointerarea in Wangyuia is 21 mm, averaging 15.4 mm life and clues to exceptional preservation of fossils. – GSA Today (60 specimens), on average about two times as long as the 11 (2): 4–8. valve length. A sketchy comparison of the pseudointerarea in Carlson, S. J. 1995. Phylogenetic relationships among extant Wangyuia chengjiangensis and Lingulellotreta malongensis from brachiopods. – Cladistics 11: 131–197.

Note on the Lower Cambrian lingulid gut • Zhang et al. Acta Zoologica (Stockholm) 88: 65–70 (January 2007)

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