Preliminary Notes on Soft- Bodied Fossil Concentrations from the Early

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Chinese Science Bulletin 2006 Vol. 51 No. 20 2482—2492 curate horizons for some genera, and findings of excep- DOI: 10.1007/s11434-005-2151-0 tionally well-preserved fossil concentrations or enrich- ment layers, which is a rare phenomenon of taphonomy and preservation. Field work by the Early Life Institute Preliminary notes on soft- (ELI), Northwest University has confirmed these fossil bodied fossil concentrations concentrations in those sections and has discovered many new such horizons, thus providing further data to from the Early Cambrian investigate the depositional palaeoenvironment of this Chengjiang deposits region in the Early Cambrian. The term ‘fossil concentration’ usually refers to HAN Jian1, SHU Degan1,2, ZHANG Zhifei1, skeletal concentration, meaning dense stacking of the LIU Jianni1, ZHANG Xingliang1 & YAO Yang1 fossils in spite of classification, preservation and de- formation of the hardparts[34]. Hardpart concentrations, 1. Department of Geology and Key Laboratory for Continental Dynam- which are very common in the fossil record, are usually ics, Northwest University, Xi’an 710069, China; controlled by sedimentation and deposition, and partly 2. School of Earth Sciences and Resources, China University of Geo- [35] sciences, Beijing 100083, China affected by diagenesis during fossilization . Fossil Correspondence should be addressed to Han Jian (email: concentrations can be made up of fossils of various [email protected]) phyla. Particularly, a fossil concentration is sometimes Received June 15, 2005; accepted September 15, 2005 composed of one species or a fossil assemblage that is Abstract The efforts of labor-intensive collecting dominated overwhelmingly by a single species; these in the Early Cambrian Chengjiang deposits in eastern types are termed ‘monospecific’ or ‘paucispecific’ con- Yunnan Province, China led to the discovery of many centration, respectively, and this phenomena of fossil horizons containing exceptionally well preserved concentration is mediated strikingly by ecology[34]. soft-bodied fossil concentrations, many of which can Such types of fossil concentrations, such as of Chuan- be assigned to either monospecific concentrations or dianella ovata, Kunmingella douvillei and hyolithids, paucispecific concentrations. The features of these are common at various sites in the Chengjiang depos- fossil concentrations support the hypothesis that its[36]. It is important to distinguish fossil concentrations frequent storm events producing tempestites mainly from fossil aggregates; the latter is characterized typi- contributed to the preservation of abundant soft- cally by a well-defined size range, a definite shape, and bodied fossils in the Chengjiang deposits, and indi- a boundary representing something like fecal pellets cate that the balance of the ecological web in this and fecal residues, or representing a recurrent composi- region was probably frequently destroyed or upset by tion in exoskeletal elements[36]. such storm events during that geological time. Ani- Comparatively, a fossil concentration with well- mals in a fossil assemblage in such fossil concentrations probably occupied similar ecological biotopes. preserved soft tissues is termed herein a ‘soft-bodied fossil concentration’ (SFC). Compared with hardpart Keywords: Early Cambrian, Chengjiang fauna, preservation, soft- concentrations, the SFC is characterized by numerous bodied fossil concentration (SFC). soft-bodied individuals occurring in the same bedding The Chengjiang fauna has played a pivotal role in plane or thin bedding layer, and can be viewed as a our understanding of the origin and diversification of specific status of fossil concentration with peculiar metazoans since its discovery in 1984. To date, this preservation, taphonomy and deposition. In particular, fauna has been documented as consisting of 121 genera an SFC fossil assemblage is sometimes also composed with 140 species belonging to 24 phyla[1－27]. The geo- of a single species or very few species with a extremely graphic distribution of the Chengjiang fauna has been dominant taxa richness; these two types are respec- expanded from Chengjiang County to eastern Yunnan tively termed ‘soft-bodied monospecific concentration’ Province including Haikou, Malong, Yiliang, Anning (SMC) and ‘soft-bodied paucispecific concentration’ and elsewhere[25－33], with about 20 localities in to- (SPC) corresponding to monospecific and paucispecific tal[25,33]. Successive excavation in recent years at the concentration sensu Kidwell[34]. Compared with hard- Ercaicun section and the Jianshan section in Haikou part concentrations, an SFC holds the promise of figur- Town, Kunming City led to the discovery of many ac- ing out comprehensively and precisely a picture of the

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ARTICLES biota in the palaeoocean The SFC might therefore re- SFCs of Cricocosmia jinningensis, Haikouella lanceo- flect faithfully the features of a natural community, lata, Phlogites longus and of Kunmingella douvillei even the population structure at that time, and thus can from the Ercaicun section, Haikou. Our field survey has provide more information on population age range identified that bedding planes with an SFC are more within a short interval. common in eastern Yunnan Province, especially in the Jianshan section (Fig. 1). Part SFCs are listed below 1 Stratigraphy with short descriptions: The Early Cambrian Heilinpu (Chiungchussu) For- (1) Porifera. A sponge, Choia sp. SFC occurs in mation was originally divided in ascending order into the upper part of the Maotianshan Mudstone Member the Shiyantou Member and the Yu’anshan Member[37]; in the Tanglipo section of Dabanqiao, Kunming. The the latter can be subdivided into a lower black shale sponge bodies of various sizes are paved on the bed- unit and an upper ‘Maotianshan Shale unit’[38] yielding ding plane. the Chengjiang Biota. Recent classification renamed A Protospongia sp. SFC occurs in the lower part of the ‘Yu’anshan Member’ as the Yu’anshan Formation Maotianshan Mudstone Member in the Haoyicun sec- consisting of four members, i.e. lower Black Siltstone tion of Xianjie, Anning. Some of specimens are com- Member, lower Black Shale Member, upper Maotian- plete, and the sponge body and large stuatins are visi- shan Shale Member and upper Siltstone Member[29,39]. ble. Because all the SFCs presented in this paper occur in (2) Discoidal fossils. Stellostomites eumorphus the later two members, we prefer the second classifica- SMC occurs in the lower part of the Maotianshan Mud- [32] tions for convenience of description in detail, and we stone Member in the Maotianshan section , propose the name ‘Maotianshan Mudstone Member’ to Shankoucun and the Haoyicun sections of Anning, Da- replace ‘Maotianshan Shale Mb. (Maotianshan Shale yucun section of Chenggong, Tanglipo section of Da- Member)’ for the lithology is dominated by mudstones banqiao as well as the middle part of the Jianshan sec- intercalated with siltstones rather than shale. tion of Haikou. Most individuals are preserved roughly parallel to the bedding planes. Most of them are com- 2 Method and materials plete adults, but occasionally include a very few Each fossil concentration in a section is exposed in smaller ones. S. eumorphus is rather sparse in other an area of approximately 2 m×10 m and the slabs ac- horizons and usually co-occurs with other types of fossils in this section. However, it is very rare in other sec- quired are generally less than 20 cm×20 cm in square tions of the Haikou region, such as Mafangcun, Er- because of the constricted conditions of fossil collec- caicun, Dazicun, and Yunlongsi. For Yunnanomedusa tion. Thus, the fossil concentration is characterized by eleganta, of the same group as S. eumorphus, its SFC thousands of slabs containing a similar fossil assem- has not been found in the Kunming and Chengjiang blage that were acquired in a thin bedding or layer by regions. It should be mentioned that the discoidal fos- successively excavating its horizons in the field. Exca- sils S. eumorphus and Pararotadiscus guizhouensis vation in a neighbor section can help recognize the dis- from the Middle Cambrian Kaili Fauna, Guizhou Prov- tribution of a fossil concentration in space. The density ince, China have been interpreted as pelagic gregarious of the fossil assemblage in a fossil concentration is av- animals[41]. eraged from part slabs that have been acquired because (3) Brachiopods. The Heliomedusa orienta mono- the densities on different slabs are not always even. specific concentration occurs in the middle part of the Illustrated specimens in this paper have been deposited Maotianshan Mudstone Member in the Jianshan section at the ELI, Northwest University, Xi’an, China. (Fig. 1); all the specimens are complete individuals similar in size. 3 Description of soft-bodied fossil concentrations The Lingulellotreta malongensis SPC with occa- Little attention has been focused on the SFC even sional Lingulella chengjiangensis occurs in the up- though this phenomenon has been widely reported for per-middle part of the Maotianshan Mudstone Member years in the localities of eastern Yunnan, such as in the Jianshan section (Fig. 1). Different individuals of Chengjiang, Malong and Wuding. Chen et al.[28－30] various sizes usually form a cluster, which is character- briefly mentioned this aspect. Wang et al.[40] reported ized by several individuals attaching their distal pedun- www.scichina.com www.springerlink.com 2483

ARTICLES cle ends intertwisted with a roughly consistent orienta- (4) Priapulids. The priapulid worms, which inhabit tion (Fig. 2(a)). Sometimes they are also scattered ran- the sediment or the interface of sediment-water, are domly on the bedding plane. present in all soft-bodied fossil localities in eastern

Fig. 1. The biostratigraphic column of the Jianshan section, Haikou, Kunming. Black block represents soft-bodied fossil concentration. Th., thickness; Coe, coelenterates; ch., chaetognaths. 1, Megaspirellus houi Chen & Erdtmann, 1991; 2, Yuknessia sp.; 3, Sinocylindra yunnanensis Chen & Erdtmann, 1991; 4, Fuxianospira gyrata Chen & Zhou, 1997; 5, Halichondrites sp.; 6, Triticispongia diagonata Mehl & Reitner in Steiner et al., 1993; 7, Proto- spongia sp.; 8, Saetaspongia densa Mehl & Reitner, 1993; 9, Paraleptumitella globula Chen et al., 1989; 10, Leptomitella conica Chen et al., 1989; 11, Choia xiaolantianensis Hou et al., 1999; 12, Crumillospongia sp.; 13, Quadrolaminiella diagonalis Chen et al., 1990; 14, Allonnia phrixothrix Bengtson & Hou, 2001; 15, Xianguangia sinica Chen & Erdtmann,1991; 16, Maotianshania cylindrica Sun & Hou, 1987; 17, Cricocosmia jinningensis Hou & Sun, 1988; 18, Palaeoscolex sinensis Hou & Sun, 1988; 19, Sicyophorus rara Luo & Hu, 1999; 20, Xiaoheiqingella peculiaris Hu in Chen et al., 2002; 21, Paraselkirkia sinica sinica Luo & Hu, 1999; 22, Tylotites petiolaris Luo & Hu, 1999; 23, Corynetis brevis Luo & Hu, 1999; 24, Microdictyon sinicum Chen et al., 1989; 25, Onychodictyon ferox Hou et al., 1991; 26, Cardiodictyon catenulum Hou et al., 1991; 27, Paucipodia inermis Chen et al., 1995; 28, Hallucigenia fortis Hou & Bergström, 1995; 29, Luolishania longicruris Hou & Chen, 1989; 30, Miraluolishania haikouensis Liu & Shu, 2004; 31, Megadictyon haikouensis Luo & Hu, 1999; 32, Facivermis yunnanicus Hou & Chen, 1989; 33, Retifacies abnormalis Hou et al., 1989; 34, Squamacula clypeata Hou & Bergström, 1997; 35, Kuamaia lata Hou, 1987; 36, Skioldia aldna Hou & Bergström, 1997; 37, Eoredlichia intermedia Lu, 1940; 38, Yunnanocephalus yunnanensis Mansuy, 1912; 39, Kuanyangia pustulosa Lu, 1941; 40, Xandarella spectaculum Hou et al., 1991; 41, Pyg- maclypeatus daziensis Zhang et al., 2000; 42, Naraoia sp.; 43, Naraoia spinosa Zhang & Hou, 1985; 44, Misszhouia longicaudata Chen et al., 1996; 45, Pectocaris eurypetala Hou et al., 2004; 46, Priminocaris subconigera Hou & Bergström,1989; 47, Isoxys auritus Jiang, 1982; 48, Isoxys paradoxus Hou, 1987; 49, Leanchoilia illecebrosa Hou, 1987; 50, Kunmingella douvillei Mansuy, 1912; 51, Chuandianella ovata Lee, 1975; 52, Clypecaris pter- oidea Hou, 1999; 53, Fuxianhuia protensa Hou, 1987; 54, Jianfengia multisegmentalis Hou, 1987; 55, Combinivalvula chengjiangensis Hou, 1987; 56, Ercaia minuscula Chen & Huang, 2001; 57, ?Tuzoia sinensis Pan, 1957; 58, Cindarella eucalla Chen et al., 1996; 59, Urokodia aequalis Hou et al., 1989; 60, Acanthomeridion serratum Hou et al., 1989; 61, Fortiforceps foliosa Hou & Bergström, 1997; 62, Yunnanocaris megista Hou, 1999; 63, Branchiocaris? yunnanensis Hou, 1987; 64, Mafangocaris multinodus Luo & Hu in Chen et al., 2002; 65, Jianshania furcatus Luo & Hu, 1999; 66, Anomalocaris saron Hou et al., 1995; 67, Amplectobelua symbrachiata Hou et al., 1995; 68, Parapeytoia yunnanensis Hou et al., 1995; 69, Burithes yunnanensis Hou et al., 1999; 70, Ambrolinevitus ventricosus Qian, 1978; 71, Glossolites yunnanensis Hou et al., 1999; 72, Linevitus opimus Yu, 1974; 73, Heliomedusa orienta Sun & Hou, 1987; 74, Lingulella chengjiangensis Jin et al., 1993; 75, Lingulellotreta malongensis Rong, 1974; 76, Dian- dongia pista Rong, 1974; 77, Botsfordia? sp.; 78, Longtancunella chengjiangensis Hou et al., 1999; 79, Eognathacantha ercainella Chen & Huang, 2002; 80, Phlogites longus Luo & Hu, 1999; 81, Vetulocystis catenata Shu et al., 2004; 82, Vetulicola rectangulata Luo & Hu, 1999; 83, Vetulicola cuneatus Hou, 1987; 84, Xidazoon stephanus Shu et al., 1999; 85, Heteromorphus confusa Luo & Hu 1999; 86, Pomatrum ventralis Luo & Hu, 1999; 87, Beidazoon venustum Shu, 2005; 88, Haikouella lanceolata Chen et al., 1999; 89, Haikouella jianshanensis Shu et al., 2003; 90, Haikouichthys ercaicunensis Luo et al. in Shu et al., 1999; 91, Zhongjianichthys rostratus Shu, 2003; 92, Stellostomites eumorphus Sun & Hou, 1987; 93, Batofas- ciculus sp.; 94, Dinomischus venustus Chen et al., 1989; 95, Calathites spinalis Luo & Hu, 1999; 96, Petalilium latus Luo & Hu, 1999; 97, Cambroten- tacus sanwuia Zhang & Shu, 2001; 98, Archotuba conoidalis Hou et al., 1999.

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Fig. 2. Soft-bodied fossil concentrations (SFC) from the Early Cambrian Chengjiang Lagerstätte. Scale bar represents 1mm. (a) Lingulellotreta malongensis from the Jianshan section of Haikou, Kunming; (b) Cricocosmia jinningensis from the Jianshan section; (c) Sicyophorus rara from the Shankoucun section of Anning; (d) Pectocaris eurypetala from the Anshan section of Haikou; (e) Ercaia inuscule from the Jianshan section; (f) Haikouella jianshanensis from the Jianshan section; (g) Haikouichthys ercaicunensis from the Jianshan section; (h) Batofasciculus sp. From the Jian- shan section. www.scichina.com www.springerlink.com 2485

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Yunnan Province. Thus the priapulid worm is generally elements of organisms parallel to the bedding plane applied as an index fossil for estimating the preserva- (Fig. 2(b)), occurs at the top of the Maotianshan Mud- tion quality of fossils at a locality. To date, 11 genera stone Member in the Jianshan section. Both kinds of and 11 species have been reported[13], but only Mao- worms lack their proboscises and their bodies are tianshania cylindrica, Cricocosmia jinningensis, Pa- curved to some degree. laeoscolex sinensis, Paraselkirkia sinica and Sicyo- A Paraselkirkia sinica fossil concentration occurs in phorus rara are found with fossil concentrations. a layer of mudstone about 5mm in thickness at the An M. cylindrica SMC occurs in the Maotianshan lower part of the Maotianshan Mudstone Member in section. Nearly all individuals are complete adults the Shankoucun section. Their bodies, with remarkable oblique to the bedding planes occasionally with drag- traces of guts and obscure proboscises, are almost ging traces (see Fig. 19 in ref. [29] and Fig. 30 in ref. completely preserved roughly parallel to the bedding [38]). planes[30,42]. Associated species are mineralized shells Three horizons of soft-bodied C. jinningensis con- of Kunmingella douvillei, fragments of Calathites spi- centrations have been recognized in the Chengjiang nalis Luo and Hu[32] and Cambrotentacus sanwuia Lagerstätte: the first C. jinningensis SPC is located in Zhang and Shu[33], isolated sclerites of lobopod Mi- the lower part of the Maotianshan Mudstone Member crodictyon sinicum and priapulid worm Tabelliscolex near the basal horizon of the Chengjiang fauna. It oc- hexagonus[9] as well as a kind of brachiopod. Chen[30] curs in a yellowish muddy siltstone with approxima- has proposed that Paraselkirkia sinica is of gregarious tely 8cm in thickness in the Haoyicun section, where all habit and that the fossil assemblage in this concentra- specimens are complete individuals with their elongate tion was buried in a disaster event. However, seen form bodies twisted to some degree and lying oblique to the the status of fossil preservation, this proposal is rather bedding planes, approximately 20 to 30 individuals per questionable. square decimeter, displaying a high ability of burrow- A Sicyophorus rara SPC with a few associated M. ing concerning the compression ratio of the mudstone. cylindrica and Xiaoheiqingella peculiaris occurs in a Usually only a small area of the body is exposed when thin bedding layer about 2cm thick in the Shankoucun the slab is split open, but they prove consequently to be section, and all specimens are complete individuals[42]. complete after preparation. Whereas the occurrence of Half of their bodies are parallel to the bedding planes the C. jinningensis SPC in the Jianshan section is simi- and the others are oblique or perpendicular to the bed- lar to that in the Haoyicun section, both of them are ding planes, having approximately 3－5 individuals per preserved in siltstone, but the latter co-occurs with square decimeter (Fig. 2(c)). Leanchoilia illecebrosa and P. sinensis. In the Tanglipo (5) Lobopods. A Cardiodictyon catenulum SMC section, C. jinningensis and P. sinensis SPC occur in a occurs in the Jianshan section and all of the specimens layer of mudstone about 5cm in thickness. are complete individuals parallel to the bedding planes. The second C. jinningensis SPC occurs in the A Facivermis yunnanicus monospecific SMC occurs Yu’anshan Member of Haikou region, usually located in the Jianshan section. All of the specimens are com- in a 10 cm-thick bed about 10 cm above the siltstone, pletely preserved with their bodies being curved or ranging from approximately 10 to 20 individuals to the twisted to some degree oblique to the bedding planes, square decimeter. Most of them are adult individuals exhibiting a feature of preservation similar to the SMC oblique to the bedding planes. C. jinningensis is found of M. cylindrica and the second SMC of C. jinningensis co-occurring with a few of the lobopods such as Mi- but less in richness. crodictyon sinicum in the Ercaicun section, with P. (6) Arthropods. A Naraoia spinosa-Naraoia sp. sinensis in the Tanglipo section and with a few paucispecific concentration occurs in the Kuangshan Paraselkirkia sinica in the Jianshan section. In section of Malong, with the specimens weathering non-concentration horizons, the body of C. jinningensis grayish white in color, and different from the general is parallel or sub-parallel to the bedding plane, and the appearance of the Chengjiang fossils in other localities. hind parts of their trunks are curved to some degree, The length of specimens ranges from 7 to 10 mm, and very few of them are straight. smaller than the average size of the specimens in other The third C. jinningensis SPC, associated with a few regions. The appendages and trace of guts are not found, P. s i ne n si s, numerous fragments of algae and other whereas the non-mineralized dorsal carapaces, which

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ARTICLES occasionally are detached into isolated head shields and three-dimensions. These specimens are almost pre- trunk shields, display a flattened appearance. The rich- served at various angles with their long body axis ness of specimens is hard to estimate because of the roughly parallel to the bedding plane. Animals of vari- extreme similarity in their carapaces and poor preserva- ous sizes are found overlapping. In the Ercaicun section, tion. individuals numbering less than 1－3 per square deci- A Misszhouia longicaudata SMC occurs in the An- meter can be recognized on the bedding plane when the shan section of Haikou. All of these specimens are rock is split out, but severely weathered fragments of complete individuals longer than 5 cm in length; their the rocks from this horizon display a greater density, bodies are generally dorso-ventrally compressed about 10－20 individuals per square decimeter. The roughly parallel to the bedding layer, with about 1－2 density seems to decrease to the east as manifested in individuals per square decimeter. the Jianshan section. Mallatt andChen[45] have proposed [43] A Pectocaris eurypetala SMC is present in a that the Haikouella animals lived in schools that were muddy bedding layer about 10 mm in thickness and just buried by the mudslides responsible for their fossiliza- 30 cm above a thick layer of 40 cm-thick sandstone in tion. the Anshan section. The eyes, the inner and outer ap- The horizon of Haikouella jianshanensis SPC (BA pendages and the trunks are visible beneath the cara- layer in Fig. 1, BA represents ‘black arthropod’, refer- paces. Most of them are laterally compressed, complete ring to Haikouella jianshanensis SPC in the field work) adults, with about 1 to 3 individuals per square deci- in the Jianshan section is lower than that of H. lanceo- meter (Fig. 2(d)). lata. Most of the specimens are laterally compressed A Pisnnocaris subconigera SMC is found in the and sagittally parallel to the bedding plane with uni- middle part of Maotianshan Mudstone Member in the form size. Some of them are randomly distributed on Tanglipo section in Kunming; most of the specimens the bedding plane and sometimes with an identical ori- are complete individuals with appendages occasionally entation. The anterior part of the animals, especially the preserved, with less than 10 individuals per square me- gill arches, are characterized by the typical leaden or ter. dark grayish color of this group, and their posterior [5] An Ercaia minuscule SPC, consisting of complete parts, however, are almost invisible with a color the individuals of this taxon and very few complete adults same as the matrix (Fig 2(f)). Occasionally, the whole of Leanchoilia illecebrosa, occurs in the Jianshan sec- bodies including their gill arches are weathered close to tion. The bodies of E. minuscule, about 2－4 mm in the color of the matrix, indicating that weathering has length and apparently less than that of L. illecebrosa, played an important role in the appearance of the are laterally compressed with a set of well-preserved Chengjiang fossils[3, 46]. The associated animals include appendages (Fig 2(e)). This SPC has proximately 5－8 a few adult individuals of the Vetulicolians Pomatrum individuals per square decimeter on a slab. ventralis, which is a swimming filter-feeding animal (7) Yunnanozoans. A Yunnannozoon lividum SFC similar to H. jianshanensis in lifestyle. In total there are occurs in the Ma’anshan section of Chengjiang County. approximately 7－10 individuals to a square decimeter. The specimens show a typical leaden color, and most of These animals are almost evenly distributed on the them are laterally compressed parallel to the bedding bedding plane in a restricted excavated area in the plane with their bodies curved to some degree. On Haikou region. The same horizon in the Anshan section some slabs they somewhat overlap (see Fig. 1(a) in ref. is similar in appearance but with the dorsal segments of [44]). H. jianshanensis being better preserved than that in the A Haikouella lanceolata SMC occurs in a thin bed- Jianshan section. ding of mudstone above a 3－5 cm-thick sandstone in (8) Vetulicolians and vetulocystids. A Xidazoon the lower part of the Maotianshan Mudstone Member stephanus SPC occurs in the Jianshan, Ercaicun and the in the Haikou region (Fig. 1). The 300 specimens of H. Anshan sections. A Didazoon haoae SPC occurs in the lanceolata mentioned by Chen et al.[4,45] were collected Tanglipo section of Dabanqiao, with complete indi- from this horizon. These specimens are complete ani- viduals. It is worthy to note that D. haoae, X. stephanus mals but their posterior part is hard to expose by and P. ventralis occur in a thin bed deep red in color in preparation[45]. Most specimens are flattened whereas the Tanglipo, Anshan and the Jianshan sections. [47] few specimens with their gill arches are preserved in The SPC of Beidazoon venustum -Vetulocystis www.scichina.com www.springerlink.com 2487

ARTICLES catenata[23] occurs in a thin bedding layer with numer- Additional examples of SFC beddings of undeter- ous fragments of algae at the middle part of the Mao- mined phyla will be described elsewhere. tianshan Mudstone Member in the Jianshan section. As noted above, SFCs are widely distributed in east- Sometimes they cannot be easily distinguished from ern Yunnan Province. Every locality with preserved each other because these two kinds of animals are al- soft-bodies fossils is associated with SFCs; therefore, most the same in size and most of them are fragments SFC can be regarded as an important feature of the having a flattened appearance, and which are grayish Chengjiang Lagerstätte. All these SFCs, except those of dark in color. The density of them on this bedding plane Stellostomites eumorphus and C. jinningensis have not is not as great as the SMC of Yunnannozoon lividum. been found contemporaneously in more than two re- Both animals are extremely sparse in the horizon of BA gions although they are almost evenly distributed on (Fig. 1). the bedding plane in a limited area, indicating a spa- A Vetulicola sp. SMC occurs below that of tially and temporally restricted character. The wide- Haikouichthys ercaicunensis[17] in the Jianshan section, spread occurrence of the SFCs in the Haikou region is and the posterior parts of the body are usually pre- somewhat related to the intensity of field work done served, of similar size. A few individuals have their because SFCs are usually confined to a thin bedding anterior parts preserved but these are poor in quality. less than 10cm in thickness, and successive excavation (9) Vertebrates. The horizon of the Haikouichthys can find more SFCs in other regions especially in the ercaicunensis SFC can be found in the middle part of Chengjiang region. Most SFCs except those of C. jin- the Maotianshan Mudstone Member in the Jianshan ningensis are not completely comparable among dif- section, and it occurs in a lamina of mudstone about 5 ferent regions. However, SFCs in neighboring sections, mm in thickness just above a 5 mm-thick sandstone such as the Shankoucun and the Haoyicun sections in with grading laminae among a suite of intercalated the Anning region, and the Ercaicun, Jianshan and the beddings of siltstone and mudstone below the horizon Anshan sections in Haikou, Kunming region can be of the SPC of Beidazoon venustum[47]-Vetulocystis used as a tool for precise biostratigraphic correlation. catenata. Most of them are adult individuals being lat- The Early Cambrian Diandong Basin can be divided erally flattened sub-parallel to the bedding planes into three sedimentary zones[33,40]. The distribution of roughly with a preferential orientation (Fig. 2(g)). Sur- the SFCs might also reflect this kind of lithological prisingly, only the anterior parts are preserved, while difference, such as in the Chengjiang and Kunming their hind parts are hard to separate from the matrix, regions, where the SFCs can be found throughout the displaying a fashion similar to that of the Haikouella Maotianshan Mudstone Member, whereas in the jianshanensis. This horizon contains a few specimens Anning region, only a few of them occur in its lower of Zhongjianichthys rostratus[22] displaying also a simi- part, and its upper part is dominated by siltstones or lar feature in preservation, and containing additional sandstones containing abundant fragmentary remains of approximately 4% complete adults of Leanchoilia ille- a variety of taxa, representing a high-energy envi- cebrosa. In total, the density in this concentration is ronment. The fossil concentration of Allonnia phrixo- about 10－20 individuals per square decimeter. Other thrix[11], which is preserved as complete individuals or specimens of H. ercaicunensis found in other sections fragments, can only be found in the Sapushan section are complete but rather rare. of the Wuding region. Palaeogeographically, the Qujing (10) Batofasciculus sp. The SMC of this taxon can region is the deepest area in the Diandong Basin with be found in the upper part of the Maotianshan Mud- less abundance and richness in fossil, and only the Na- stone Mb. in the Jianshan section, and all of the speci- raoia spinosa fossil concentration have been found in mens appear as discrete fragmental straight branches that region. Thus, the SFCs are abundant in the south- parallel to the bedding plane with a consistent orienta- west of the basin, corroborating the palaeoenvironmen- tion (Fig. 2(h)). This concentration can also be found in tal analysis that the basin is a restricted bay opening to the Anshan section of Haikou (Hu S., personal commu- the south as inferred from the Xiaojiang fault[25]. How- nication). Several complete specimens of B. ramificans ever, the differences in sedimentary facies among the have been found in the Maotianshan[38] and the regions in eastern Yunnan Province do not constrain a Shankoucun sections, and morphologically, its arc-like species in a single section. A species that is common in branches differ from the straight forms of B. sp. a section can also be rare or absent in another section

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ARTICLES despite the intensity of labor. For example, in the rapid burial. Taking this together with the lithological Chengjiang region, Vetulicola cuneata is comparably evidence of the tempestites[35,39], it stands to reason that common, whereas its sister species Vetulicola rectan- the widespread occurrence of the SFCs was formed gulata has never been reported; the latter species is during frequent storms with rapid burial. common in the Haikou and Anning regions, where only Some SFCs, for example, the third one of C. jinnin- a few specimens of V. cuneata have been found recently. gensis in the Jianshan section (Fig. 2(b)) and that of Therefore, it could be argued that the difference in the Paraselkirkia sinica in the Shankoucun section, are various sedimentary facies did not stand as barriers to characterized by incomplete individuals, with poor isolate the species, but it apparently mediated the rich- quality in preservation, and a fossil assemblage with ness of the animals. Our intense field survey over a various fragments of organism, etc., and were possibly large area supports the fact that more than one species formed by slow stacking rather than rapid burial, thus are sometimes found in a concentration, which in turn they are not included in discussion below. reveals that a concentration first regarded as an SMC is actually an SPC. 5 Palaeoecology 5.1 The fossil assemblage occurring at an SFC most 4 Preservation and taphonomy likely representing a statistical community The mechanisms and processes of the Chengjiang [54] Lagerstätte in preservation and taphonomy have been Hallam has characterized the concept of a statis- [29,48－50] tical population to distinguish it from the normal fossil widely hypothesized and are still in debate . populations that are formed by the gradual stacking of Evidence coming from lithology supports the hypothe- hardparts in a stratigraphical interval. A statistical sis that tempestite rocks can account for the abundant preservation and wide distribution of soft-bodied population is usually formed by a catastrophic event Chengjiang fossils[35]. Most of the Chengjiang fossils that leads to a simultaneous burial of all living things in are preserved as aluminosilicate films, similar to the that region, and generally can be found in thin beddings host rocks[29]; some of them have been completely pyri- or on a single bedding plane containing very few species, and the adjacent horizons are almost non-fossi- tized, and organic carbon can be occasionally traced on [54] some hardpart fossils[50]. Zhang and Shu[51] argued that liferous , consisting with the features of SFCs from the rapid mineralization of the body surface rather than the Chengjiang deposits. On the one hand, different rapid burial was the key factor in inhibiting the decay individuals of the same taxon in the same SFC are gen- of the body. No matter which factor has promoted the erally uniform in size and in quality of preservation, soft-bodied preservation, all Chengjiang fossils known indicating that they had undergone the same transport- come from the mudstone of the Maotianshan Mudstone ing or burial process, whereas individuals belonging to Member, while the siltstone has only provided hard- different taxa sometimes are different in size and pres- parts. However, the finding of the soft-bodied C. jin- ervation probably because their bodies exhibit different ningensis concentrations in the Jianshan and Haoyicun responses or reactions to the taphonomic processes. For sections indicates that muddy siltstone can also be the example, Leanchoilia illecebrosa fossils in the host rock for exceptional fossil preservation. Haikouichthys ercaicunensis SPC are complete Whether the Chengjiang fossils have been deposited whereas most hind bodies of H. ercaicunensis are in situ or were transported from elsewhere is still con- poorly preserved; Pomatrum ventralis fossils are better troversial[52,53]. The finding of SFCs seems to support qualified than H. jianshanensis in completeness in the the storm hypothesis: some SFCs except that of the H. jianshanensis SFC. On the other hand, these SFCs infauna are current-aligned along the bedding plane containing few species generally occur in thin bedding (Fig. 2(a), (d), (g), (h)), indicating a phenomenon of planes or a single bedding plane and lack fossils in ad- transporting; but the distance of transport and whether jacent horizons. Combined with evidence of tempes- they have been sorted are hard to discern. Additional tites[35,39], it is reasonable to regard the same species in evidence is that these SFCs lack any trace of bioturba- a fossil assemblage in such an SFC as a statistical tion. Some dragging traces that have been found around population mostly close to the original picture of the [42] the bodies of priapulid worms are very short , most living population; the fossil assemblages in an SFC can likely indicating a phenomenon of death struggle after closely represent a regional ancient community given www.scichina.com www.springerlink.com 2489

ARTICLES the limitations of fossil preservation; the overwhelming in this paper are known from sponges, coelenterates, species of this assemblage probably represents a natu- priapulid worms to arthropods, lobopods, lophophorans rally dominant species in that region. as well as deuterostomes preferring diverse life styles Taxa of a fossil assemblage in an SFC generally such as infaunal habit, epibenthic sessile habit, benthic possess a similar type of locomotion, and some of them crawling and benthic swimming, as well as mobile pe- occupy the same or adjacent ecological niches. The lagic habits. Therefore, most populations at that time mobile pelagic forms are illustrated by the SFCs of H. could hardly escape from storms. The pioneer species jianshanensis and H. ercaicunensis noted above; the after storms would have quickly recovered and were infaunal forms by P. s i ne n sis in the C. jinningensis SFC able to flourish in that region due to lack of predators or as well as Xiaoheiqingella peculiaris in the Sicyopho- other competitors, and were quickly buried as an SFC rus rara SPC. However, a few of the individuals of by the storms later on. The dominant taxon at an SFC Leanchoilia illecebrosa in the C. jinningensis SPC might represent an opportunistic species during the re- probably are exceptional; they are heterogeneous with covery of their ecosystem. The episodic storms would the associated C. jinningensis because these two groups have prompted the refreshing of the local dominant strikingly differ from each other in lifestyle. species. The non-fossiliferous horizons illustrate that the re- 5.2 The dominant species in an SFC probably pos- construction of a food web in the ecological pyramid sessing a gregarious habit needs a certain span of time. Probably the infaunal The richness of a species in a section is mediated by burrowing taxa and the nektonic filtering forms will spatio-temporal factors and taphonomy. Fossil concen- immigrate first into a virgin environment followed by trations caused by slow transportation of hardparts like the benthic forms; the appearance of the giant predators, a skeleton concentration can not be applied as evidence which generally are regarded as a representative of of gregarious habit of the overwhelming species in the equilibrium species occupying the top of the ecological fossil assemblage; on the contrary, a single species oc- pyramid, represents the complete recovery of their curring exclusively in an SPC formed by rapid burial ecosystem[29,32]. But this process is possibly mediated can be regarded as strong evidence to support its gre- by the nature of the substrate. For example, the benthic garious habit, partly because the prerequisite for an filter sponges and chancellorids could anchor in the soft SFC is that there was a flourishing natural population muddy sediment, whereas the benthic sessile forms or a swarm of a species once living in the ancient ocean. such as Cheungkongella ancestralis, Phlogites longus, On the contrary, a rare species in a section could also Archotuba conoidalis, Dinomischus venustus and the not support its solitary nature, for example, C. jinnin- linguloids apply the ecdysis of trilobites, especially the gensis is extremely rich in the Anning and Haikou re- cheeks, or the shells of brachiopod Diandongia pista gions, but very rare in the Chengjiang region. Seen and hyloliths[20,26] as a hard supporting base anchoring from the known SFCs and based on our extensive sur- in the soft muddy deposits. A kind of small epibiont of vey, we suggest that the gregarious habit was common problematic affinity is also found attaching to the sur- in Early Cambrian ocean communities. face of these hardparts[42], indicating that these forms appeared later during the ecological restoration. 5.3 An SFC probably representing firstly a group de- Chen et al.[29,30] estimated that there are less than 20 mise event and a recovery event in a region recovering events through the Maotianshan Mudstone The muddy tempestite rocks between SFCs and the Member in eastern Yunnan. Concerning the nature of siltstones are usually non-fossiliferous. Geochemical SFCs that could promise to provide accurate data in this analysis results show that these rocks are affected by aspect, we conceive that there are less than 16 such freshwater[39]. The periodical storms have frequently events in the Jianshan section where up to 16 horizons destroyed local ecosystems[25,32]. The abundant fossils of SFCs have been found. The BA layer in the Jianshan in the SFC might reflect the mass demise events to section, which is located just above the lowest horizon some extent. Hagadorn[55] has proposed that some pe- of the soft-bodied Chengjiang fossils and the underly- lagic forms could escape from storm disaster. Possibly ing black shale (see Fig. 1), most likely represents the the infaunal forms could also escape from the disaster first flourish of the Chengjiang fauna on account of the events by burrowing. However, fossil SFCs illustrated vast majority of taxa including some representatives of

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ARTICLES deuterostomes found in that horizon. References Vannier and Chen[56] have proposed that the living space of the Chengjiang biota is not constrained to the 1 Chen A, Feng H, Zhu M, et al. A new Vetulicolian from the Early Cambrian Chengjiang fauna in Yunnan of China. Acta Geol Sin, lower level of the water, and that some pelagic forms 2003, 77(3): 281－287 have exploited the midwater environment of the sea. 2 Chen J, Dzik J, Edgecombe G D, et al. A possible Early Cambrian Our analysis on SFCs is consistent with this idea, but chordate. Nature, 1995, 377: 720－722[DOI] the actual case would be more complicated concerning 3 Chen J, Zhou G. Biology of the Chengjiang Fauna. Taichung: Bul- many active pelagic forms of arthropods such as Isoxys letin of the National Museum of Natural Science, 1997, 10: 33－37 auritus, Branchiocaris yunnanensis, Naraoia spinosa 4 Chen J, Huang D, Li C. An Early Cambrian craniate-like chordate. that appeared below the horizon of the Haikouichthys Nature, 1999, 402: 518－522[DOI] SPC, but none of them have been found in this SPC. As 5 Chen J, Vannier J, Huang D. The origin of crustaceans: new evi- mobile swimmers, the yunnaozoans, vetulicolians and dence from the Early Cambrian of China. Porc R Soc Lond, 2001, Vetuloicystids, H. ercaicunensis, as well as the chor- 68: 2181－2187 dates Cathyamyrus diadexus and Zhongxiniscus inter- 6 Chen J, Huang D. A possible Lower Cambrian Chaetognath (arrow worm). Science, 2002, 98 (4): 187[DOI] media[1－4,17－19,21－23,25,45,57] are filter feeders, but they 7 Chen J, Huang D, Peng Q, et al. The first tunicate from the Early did not appear in the same SFC; and some of them Cambrian of South China. Proc Nat Acad Sci USA, 2003, 100: flashed in only once in the strata records, so that the 8314－8318 questions above need further consideration. Seen from 8 Chen J, Waloszek D, Maas A. A new ‘great-appendage’ arthropod the appearances of other types, one storm event cannot from the Lower Cambrian of China and homology of Chelicerae and lead to the entire extinction of a dominant species in raptorial antero-ventral appendage. Lethaia, 2004, 37: 3－20[DOI] fossil concentrations. 9 Han J, Zhang X, Zhang Z, et al. A new platy-armored worm from the Early Cambrian Chengjiang Lagerstätte, South China. Acta Geol 6 Conclusions Sin, 2003, 77(1): 1－6 10 Han J, Zhang Z, Liu J, et al. The earliest-known ancestors of Recent (1) Wide distribution of SFCs in the Chengjiang Priapulomorpha from the Early Cambrian Chengjiang Lagerstätte. Lagerstätte of eastern Yunnan supports the hypothesis Chin Sci Bull, 2004, 49(17): 1860－1868 that frequent storms were the main factor in preserva- 11 Hou X, Aldridge R J, Bergström J, et al. The Cambrian Fossils of tion of abundant soft-bodied fossils. Storms in the Early Chengjiang, China: the Flowering of the Early Animal Life. Oxford: Cambrian Diandong Basin were mainly concentrated in Blackwell Publishing Company, 2004. 233 the south part of this area. The occurrence of SFCs is 12 Huang D, Vannier J, Chen J. Recent Priapulidae and their Early mediated by palaeogeography, palaeoenvironment and Cambrian ancestors: comparisons and evolutionary significance. palaeoecology. Geobios, 2004, 37: 217－228[DOI] (2) The fossil assemblage occurring at an SFC most 13 Huang D, Vannier J, Chen J. Anatomy and lifestyles of Early likely represents a statistical community in a short in- Cambrian priapulid worms exemplified by Corynetis and Anning- vermis from the Maotianshan Shale (SW China). Lethaia, 2004, 37: terval; the dominant species in that assemblage most 21－33 likely possessed a gregarious habit; all species in that 14 Huang D, Vannier J, Chen J, et al. Early Cambrian Sipunculan assemblage can be speculated as probably occupying a worm from southwest China. Proc R Soc Lond, 2004, B271: 1671 similar ecological niche; an SFC layer probably repre- －1676[DOI] sents periodically a group demise event and a recovery 15 Liu J, Shu D, Han J, et al. A rare lobopod with well－preserved event in local ecosystems. eyes from Chengjiang Lagerstätte and its implications for origin of arthropods. Chin Sci Bull, 2004, 49(10): 1063－1071 Acknowledgements The authors offer their heartfelt thanks 16 Maas A, Waloszek D, Chen J. Phylogeny and life habits of early to Dr. S. Turner and Prof. K. Yasui for improving English. arthropods－predation in the Early Cambrian sea. Prog in Nat Sci, Thanks are given to Dr Hu S. of Yunnan Geological Institute 2004, 14: 124－132 and two anonymous experts for providing constructive ad- 17 Shu D, Luo H, Conway M S, et al. Lower Cambrian vertebrates vices. Thanks are also due to Cheng Meirong, Zhai Juanping from South China. Nature, 1999, 402: 42－46[DOI] for photography; and Guo Hongxiang and Ji Yanbing for 18 Shu D, Conway M S, Zhang X, et al. A Pipiscid-like fossil from the fossil collections. This work was supported by the National Lower Cambrian South China. Nature, 1999, 400: 746－749[DOI] Natural Science Foundation of China (Grant Nos. 40332016, 19 Shu D, Conway M S, Han J, et al. Primitive deuterostomes from the 32070207), the Program for Changjiang Scholars and Inno- Chengjiang Lagerstätte, Lower Cambrian, China. Nature, 2001, 41(4): vative Research Team in University (PCSIRT). 419－424[DOI] www.scichina.com www.springerlink.com 2491

ARTICLES

20 Shu D, Chen L, Han J, et al. An Early Cambrian tunicate from Formation in Chengjiang County, Eastern Yunnan in The Cambrian China. Nature, 2001, 411: 472－473[DOI] System of South China. Acta Palaeont Sin, 2001, 40 (Sup.): 80－ 21 Shu D, Conway M S, Zhang Z, et al. A new species of Yunnano- 105 zoan with implications for Deuterostome Evolution. Science, 2003, 40 Wang H, Zhang J, Hu S. Litho- and Biostratigraphy of the Lower 299: 1380－1384[DOI] Cambrian Yu’anshan Formation near the village of Ercaicun, Hai- 22 Shu D. A paleontological perspective of vertebrate origin. Chin Sci kou Couuty, eastern Yunnan Province, China. In: Peng S, Babcock Bull, 2003, 48(8): 725－735 L E, Zhu M, eds. The Cambrian System of South China. Acta Pa- 23 Shu D, Conway M S, Han J, et al. Ancestral echinoderms from the laeont Sin, 2001, 40 (Sup.): 106－114 Chengjiang deposits of China. Nature, 2004, 430: 422－428[DOI] 41 Zhu M, Zhao Y, Chen J. Revision of the Cambrian discoidal ani- 24 Zhang X, Han J, Shu D. New occurrence of the Burgess Shale ar- mals Stellostomites eumorphus and Pararotadiscus guizhouensis thropod Sidneyia in the Early Cambrian Chengjiang Lager- from South China. Geobios, 2002, 35:165–185[DOI] stätte(South China), and revision of the arthropod Urokodia. Al- 42 Han J, Zhang Z, Liu J. Taphonomy and ecology of the introverts cheringa, 2002, 26: 1－8 from the Chengjiang fauna. Journal of Northwest University (in 25 Chen L, Luo H, Hu S, et al. Early Cambrian Chengjiang Fauna in Chinese), 2004, 34(2): 206－211 Eastern Yunnan, China (in Chinese). Kunming: Yunnan Science 43 Hou X, Bergström J, Xu G. The Lower Cambrian Crustacean Pec- and Technology Press, 2002. 199 tocaris from the Chengjiang Biota, Yunnan, China. J Paleont, 2004, 26 Zhang Z, Han J, Liu J. A new linguliform brachiopod from the 78(4): 700－708 Chengjiang. J Northwest Univ (in Chinese), 2004, 34(2): 207－212 44 Shu D, Zhang X, Chen L. Reinterpretation of Yunnanozoon as the 27 Sun W, Hou X. Early Cambrian worm from Chengjiang, Yunnan, earliest known hemichordate. Nature, 1996, 380: 428－430 China. Acta Palaeont Sin (in Chinese), 1987, 26 (3): 299－306 45 Mallatt J, Chen J. Fossil sister group of craniates: Predicted and 28 Zhu M, Zhang J, Hu S, et al. The Early Cambrian Chengjiang Biota: found. J Morphol, 2003, 258: 1－31[DOI] New quarry and discoveries near Ercaicun, Haikou town, Kunming 46 Butterfield N J. Leanchoilia illecebrosa guts and the interpretation county, Yunnan province, China. In: Peng S, Babcock L E, Zhu M, of three-dimensional structures in Burgess Shale-type fossils. Pa- eds. The Cambrian System of South China. Palaeoworld, 2001, 10: laeobiology, 2002, 28(1): 155－171 236－238 47 Shu D. On the phylum Vetulicola. Chin Sci Bull, 2005, 50(20): 29 Chen J, Zhou G. Biology of the Chengjiang Fauna. Taichung: Bul- 2342－2354 letin of the National Museum of Natural Science, 1997. 10: 33－37 48 Briggs D E G. The role of decay and mineralization in the preserva- 30 Chen J Y. The Dawn of Animal World (in Chinese). Nanjing: tion of soft-bodied fossils. Ann Rev Earth Planet Sci, 2003, 31: 275 Jiangsu Science and Technology Press, 2004. 1－188 －301 31 Hou X, Sun W. Discovery of the Chengjiang fauna in the Meishu- 49 Butterfield N J. Exceptional fossil preservation and the Cambrian cun, Jinning, Yunnan. Acta Palaeont Sin (in Chinese), 1998, 27, 1 explosion. Integ Comp Biol, 2003, 43(1): 166－177 －12 50 Gabbott S E, Hou X, Norry M J, et al. Preservation of Early Cam- 32 Luo H, Hu S, Chen L, et al. Early Cambrian Chengjiang Biota from brian animals of the Chengjiang biota. Geology, 2004, 32 (10): Kunming Region, China (in Chinese). Kunming: Yunnan Science 901–904[DOI] and Technology Press, 1999. 129 51 Zhang X, Shu D. Preservation mechanisms of nonbiomineralized 33 Zhang X, Shu D, Li Y, et al. New sites of Chengjiang fossils: Cru- animal tissue. Acta Sediment Sin (in Chinese), 2001, 19(1):14－19 cial windows on the Cambrian explosion. J Geol Soc London, 2001, 52 Hou X, Chen J, Lu H. Early Cambrian new arthropod from Cheng- 158: 211－218 jiang, Yunnan. Acta Sedimentol Sin (in Chinese), 1989, 28(1): 42－ 34 Kidwell S M. Conceptional framework for the analysis and classi- 57 fication of fossil concentration. Palaios, 1986, 1: 228－238 53 Jin Y, Wang H, Wang W. Palaeoecological aspect of branchiopods 35 Zhu M. Taphonomy of the Chengjiang Fossils, Yunnan. Nanjing from Chiungchussu Formation of Early Cambrian Age, Eastern Institute of Geology and Palaeontology, CAS. 1992 Yunan, China. Palaeoecology of China, 1991, 1: 25－47 36 Vannier J, Chen J. Early Cambrian food chain: New evidence from 54 Hallam A. Models involving population dynamics. In: Schopf T J fossil aggregates in the Maotianshan Shale Biota, SW China. M, ed. Models in Paleobiology. San Francisco: Freeman Cooper Palaios, 2005, 20: 3–26 and Co, 1972. 62－80 37 Luo H, Jiang Z, Tang L. The Lower Cambrian Stratatype Sections 55 Hagadorn J W. Chengjiang: Early records of the Cambrian explo- of China (in Chinese). Kunming: Yunnan Science and Technology sion. In: Bottjer D J, Etter W, Hagadorn J W, et al. eds. Exceptional Press, 1994. 1–183 Fossil Preservation: A Unique View on the Evolution of Marine 38 Hou X, Bergström J, Wang H, et al. The Chengjiang Fauna: Excep- Life, New York: Columbia University Press, 2002. 35－60 tionally Well-preserved Animals from 530 Million Years Ago (in 56 Vannier J, Chen J. The Early Cambrian colonization of pelagic Chinese). Kunming: Yunnan Science and Technology Press, 1999. niches exampled by Isoxys (Arthropoda). Lethaia, 2000, 33: 295－ 53–64 311[DOI] 39 Zhu M, Zhang J, Li G. Sedimentary environments of the Early 57 Luo H, Hu S, Chen L. New Early Cambrian chordates from Haikou, Cambrian Chengjiang Biota: Sedimentology of the Yu’anshan Kunming. Acta Geol Sin, 2001, 75(4): 345－347

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