寒武纪大爆发———早期后生动物辐射之谜:序言*

<正>随着中国经济的持续、稳定发展和国家政府对基础研究的日趋重视,我国科技投入力度正在逐年加大,包括古生物学在内的地球科学基础研究近十年来取得长足的进步和发展。近些年,我国的古生物学已开始在多门类起源、系统演化和环境背景研究中处于国际领先,在部分研究方向开始发挥重要国际引领作用。加之华南、华北保存的化石材料优势和若干国家重大项目的稳定、持续支持(Zhu et al.,2016a;Zhu and Li,2017),使我国在科研队伍、     

A new eocrinoid fauna (Cambrian Series 2) from Guizhou Province,South China

A new eocrinoid locality of the Balang Formation (Cambrian Series 2) near Kaili City is reported. The fauna is associated with index trilobites, such as Redlichia (Pteroredlichia) murakamii Resser and Endo in Kobayashi, 1935 and Arthricocephalus chauveaui Bergeron, 1899, that are common in the Balang Biota (Cambrian Series 2) but absent in the younger Kaili Biota (Cambrian Series 3). This new locality contains a new eocrinoid fauna (n = 22) that is different from Guizhoueocrinus yui Zhao, Parsley and Peng, 2007a in bearing a smaller theca, a shorter stalk, and a robust attachment disk; thus, a taxon Globoeocrinus zhaoyuanlongensis n. sp. is proposed.     

The soft anatomy of Isoxys minor from the Guanshan fauna,lower Cambrian of Southwest China

Isoxys is a very common Cambrian bivalved arthropod, specimens of which are normally preserved only as valves. The discovery of the soft anatomy of Isoxys may greatly assist understanding affinities and functional morphology. Isoxys minor Luo and Hu in Luo et al., 2008 is the most common representative of all animal species known from the lower Cambrian Guanshan fauna (Cambrian Series 2, Stage 4) at the Shitangshan Section, near Kunming, Yunnan Province, Southwest China. Here we describe and reconstruct the morphology of I. minor on the basis of newly illustrated fossils and a few new specimens that bear soft-parts including new discovery of frontal grasping appendages. Like the soft anatomy of other known Isoxys, it bears a pair of large stalked eyes, a pair of specialized frontal grasping appendages, approximately 12–14 paired biramous limbs, and a helm-like tail exposed outside the valves.     

First report of Schizopholis (Lingulata,Brachiopoda) from the Tsinghsutung Formation (Cambrian Series 2, Stage 4) in Guizhou,China

Schizopholis Waagen, 1885 is a genus of linguliform brachiopod, which is known from Cambrian Stage 4 to the Wuliuan Stage of Australia, Antarctica, Pakistan and China. Recently, new material of Schizopholis was discovered from the upper part of the Tsinghsutung Formation (Cambrian Series 2, Stage 4) near Balang village, Jianhe County, Guizhou Province, China. These specimens display the oval pedicle opening in the ventral valve, a median tongue and a pair of tubercles in the dorsal valve that are characteristic features of Schizopholis napuru (Kruse, 1990). This is the first time that this species has been described from Guizhou Province, China. Previously, fossils of this species are usually preserved in carbonate deposits, but the new material documented herein preserved in mudstone of the Tsinghsutung Formation, providing new information regarding both the paleogeographic distribution and paleoecology of this species.     

Early Cambrian radiolarians and sponge spicules from the Niujiaohe Formation in South China

Most of the reported Cambrian radiolarians are from middle Cambrian (Miaolingian Series, Wuliuan Stage) and onward, the radiolarians from lower Cambrian (Terreneuvian and Cambrian Series 2), on the other hand, are poorly documented, thus their morphological characteristics have not been well understood. In this study, we extracted spherical radiolarians and sponge spicules from the chert of the Cambrian Series 2 Niujiaohe Formation in southern Jiangxi Province, China. The well-preserved radiolarian fossils, identified as Paraantygopora porosa, consist of perforate plate shells pierced by dense pores with elevated rims, and display similarities to those from Lower Ordovician. Seven forms of sponge spicules are recognized, including monaxons, diaxons, tetractines, hexactines, triaxon tetractines, triaxon pentactines and irregular tetraxon tetractines, which are similar to those from the Qiongzhusian Stage in South China. Our results, combined with previously reported early Cambrian radiolarians from South China, indicate that the early Cambrian radiolarians developed advanced spherical skeletons.     

葫芦虫化石在寒武纪关山生物群中的发现及其意义

报道产自昆明高楼房的寒武纪早期关山生物群中的葫芦虫化石,这是该类动物在全球的第三例化石记录。葫芦虫化石在关山生物群的发现对了解该类动物以及寒武纪动物群生态和演化等均有着重要意义。     

The Cambrian brachiopod fauna from the first-trilobite age Shuijingtuo Formation in the Three Gorges area of China

The Yangtze platform of South China offers evidence within its Ediacaran–Cambrian geological record of the Cambrian explosion and diversification events in metazoan history. To understand the explosive radiation of animals and the environments in which it took place, the basal Cambrian fauna succession of the Aijiahe section in the Three Gorges area, western Hubei Province, has been studied, revealing the earliest brachiopod fauna (Tsunyidiscus trilobite Zone) in this region, which was dominated numerically by acrotretoids. This is accompanied by abundant skeletal fossils including minute well-preserved phosphatized archaeocyath cups and an assortment of abundant sponge spicules, chancelloriids, mollusks, hyoliths, and bradoriids, retrieved by acid-etching limestone interbeds in the black shale-dominated Shuijingtuo Formation (Series 2). The brachiopods comprise two species of acrotretoids, two types of botsfordiids (Botsfordiidae gen. et sp. indet. A and B), and four species of linguloids. Of the latter, Spinobolus popovi n. gen. n. sp. is strikingly distinctive and typified by spine-like ornamentation seen for the first time in the lower Cambrian; the remaining three linguloid genera, Palaeobolus, Eoobolus, and Lingulellotreta, have a trans-paleocontinental distribution. The Three Gorges Shuijingtuo brachiopod assemblage differs from that of the upper Atdabanian Stage (Cambrian Stage 3) in Siberia and South China, but shows great similarities with those discovered in the Tsanglangpuan (equivalent to Botoman or Stage 4) Stage of eastern Yunnan Province, Siberia, and South Australia, suggesting a much more prolonged sedimentary hiatus in basalmost Shuijingtuo Formation of the Three Gorges area than previously expected. The presence of such unconformities provides a caveat to stable isotope-based correlations that involve a number of discussions of global ocean geochemical changes across the time interval that witnessed Cambrian explosion of metazoans.     

Feeding strategy and locomotion of Cambrian hyolithides

The Chengjiang (Cambrian Stage 3) and Balang (Cambrian Stage 4) Konservat-Lagerstätten of South China have produced abundant hyolithide hyoliths; however, little attention has been paid to their feeding strategy and the role it played in the ecosystem. Hyolithides preserved in coprolites from the Chengjiang Biota and associated with a Tuzoia carcass from the Balang Fauna reveal the fluid feces consuming and scavenging strategies of this group. Size distribution of hyolithides demonstrates that their dietary habit is ontogenetically dependent, with juveniles having ingested organic-rich material whereas adult food consumption was more likely by a variety of species-dependent methods The first discovery of hyolithides in association with locomotion traces and burrows indicates they were not only epibenthic vagrants, but also shallow horizontal burrowers. The new discoveries reported herein enhance our understanding of the feeding strategy and other behaviours of Cambrian hyolithides.     

Oldhamia radiata: the trace of an undermat miner from the Cambrian Series 2 Xinji Formation,western Henan,North China

Oldhamia trace fossils represent a complex horizontal burrow system usually associated with microbial mats, occurring in the upper part of the Cambrian Stage 2 of the Terreneuvian Series, with a peak in abundance during Stage 3 and 4 of Series 2, and then rapidly disappearing in the Wuliuan Stage of the Miaolingian Series. We here report Oldhamia radiata from the Cambrian Series 2 Xinji Formation in western Henan of North China, associated with microbial mats, as evidenced by the presence of wrinkle structures. The distinctive patterns indicate the exploitation of microbial mats by the tracemakers of O. radiata, featuring a specific feeding strategy under the mats where possibly anoxic and sulfidic conditions prevailed during the early Cambrian.     

A new rhynchonelliform brachiopod Longtancunella with soft-part preservation from the Hongjingshao Formation (Cambrian Stage 3) in Yunnan,South China

Rhynchonelliform brachiopods made their first appearance in early Cambrian, and became a major group within the palaeozoic evolutionary fauna since late Cambrian. Exceptionally preserved fossils from the early Cambrian Lagerstätten provide valuable chances to investigate their phylogeny and ecology. Longtancunella is one of the most interesting early rhynchonelliforms, and has been mainly recovered from the Chengjiang Lagerstätte (Series 2, Stage 3). Here, we report a new rhynchonelliform Longtancunella xiazhuangensis n. sp. from the lower Hongjingshao Formation (upper Stage 3) in Yunnan Province, China. These specimens were well preserved with soft parts, including pinnate mantle canal system and a pedicle. It is identified as a new species based mainly on its difference in shell ornamentations, pinnate mantle canals and pedicle morphology from the type species. Its pedicle looks unusually stout with distinct annulated lamellae on the surface, and reveals crucial evidence in illustrating its ecology and settling strategy as an early marine epifauna. The ecological interaction between L. xiazhuangensis and other marine animals also provides insights into the food web structure in the early Cambrian.     

Cambrian trilobite fauna of the Haydenaspis parvatya level (Series 2, Stage 4): Its stratigraphic position with respect to the Oryctocephalus indicus Biozone (Miaolingian Series,Wuliuan Stage) in the Spiti Himalaya,India

Refinement of the Cambrian biozonation in the Parahio valley, Spiti region (Himalaya) leads to the demarcation of the stratigraphic distance between the Haydenaspis parvatya level (Series 2, Stage 4) and the Oryctocephalus indicus Biozone (base of the Miaolingian Series, Wuliuan Stage), which has been a subject of debate. The present work suggests that these two trilobite beds in the Kaltarbo section are separated by 183.4 m of strata. Whether either taxon ranges beyond the beds they are found in this section or others in the Parahio Valley is yet unknown.     

Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution—but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum—as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.     

A crown‐group demosponge from the early Cambrian Sirius Passet Biota,North Greenland

Calibration of the divergence times of sponge lineages and understanding of their phylogenetic history are hampered by the difficulty in recognizing crown versus stem groups in the fossil record. A new specimen from the lower Cambrian (Series 2, Stage 3; approximately 515 Ma) Sirius Passet Biota of North Greenland has yielded a diagnostic spicule assemblage of the extant demosponge lineages Haploscleromorpha and/or Heteroscleromorpha. The specimen has disarticulated approximately in situ, but represents an individual sponge that possessed monaxon spicules combined with a range of slightly smaller sigma, toxa and unique spiral morphologies. The combination of spicule forms, together with their relatively large size, suggests that the sponge represents the stem lineage of Haploscleromorpha + Heteroscleromorpha. This is the first crown‐group demosponge described from the early Cambrian and provides the most reliable calibration point currently available for phylogenetic studies.     

A new family of Cambrian rhynchonelliformean brachiopods (Order Naukatida) with an aberrant coral‐like morphology

Tomteluva perturbata gen. et sp. nov. and Nasakia thulensis gen. et sp. nov., two new rhynchonelliformean brachiopod taxa, are described from carbonate beds from the lower middle Cambrian (Series 3, Stage 5) basinal Stephen Formation, Canada, and the upper lower Cambrian (Series 2, Stage 4) Henson Gletscher Formation, North Greenland, respectively. The two taxa are characterized by an unusual coral‐like morphology typified by a high conical ventral valve with an anteriorly curved umbo and a tube‐like structure inside the ventral valve, interpreted as pedicle tube. Both resemble the problematic late middle Cambrian (Drumian) species Anomalocalyx cawoodi Brock from Australia, whose systematic affiliation is controversial. Together, the three genera are interpreted as representatives of a new family of rhynchonelliformean brachiopods, the Tomteluvidae fam. nov., which is interpreted as an aberrant or derived taxon within the Order Naukatida. Convergence between the Tomteluvidae and the coralla of small solitary Cambrian coralimorphs, as well as the late Palaeozoic reef‐building richthofenioid brachiopods, might indicate adaptation to a similar life habits and environments. However, their small size (length 4 mm), well‐developed pedicle and perfect morphological symmetry make it more likely that tomteluvids lived attached to frondose algae or sponges, above the seafloor, in a similar fashion to the acrotretoid brachiopods with which they show a high degree of morphological convergence. Morphological features of the pedicle tube of N. thulensis suggest that the tomteluvid pedicle is homologous to that in modern rhynchonelliformean brachiopods. This is the first evidence of the pedicle type within the Naukatida and represents the oldest confirmation of a rhynchonellate pedicle.     

A new early Cambrian bivalved euarthropod from Yunnan,China and general interspecific morphological and size variations in Cambrian hymenocarines

The hymenocarines were a major and diverse group of euarthropods featured by a bivalved head carapace and a segmented trunk comprising tergo-pleural rings notably from the Cambrian Burgess Shale-type Lagerstätten. Here we document a new ~50 mm long hymenocarine Xiazhuangocaris chenggongensis n. gen. n. sp. from the Xiazhuang fossil assemblage, a slightly younger occurrence of the Chengjiang Lagerstätte within the lower Cambrian Hongjingshao Formation (Cambrian Series 2, Stage 3) in Chenggong, Yunnan, southwestern China. X. chenggongensis is characterized by the bivalved carapace with each valve bearing a protruded anterior tip and a prominent posterior notch, which resembles the P-element of the radiodont Hurdia and is unique among the hymenocarines. The trunk consists of at least 13 tergo-pleural rings including presumably eight abdominal ones terminating in a pair of ovate caudal rami. With the body organization and morphological features closest to waptiids, X. chenggongensis represents a ‘larger’ waptiid-like hymenocarine. The morphometric analysis recognizes the family-level groupings of Cambrian hymenocarines based on the number of tergo-pleural rings and the proportion of exposed trunk length, indicating that these are useful characters for studying hymenocarine morphology and phylogeny. Cambrian hymenocarines exhibited great interspecific body size variations even between sister species of the same family, further suggesting that niche diversification happened on the family level and even among phylogenetically close genera or species during the Cambrian explosion.     

Morphology,ontogeny, and heterochrony in lower and middle Cambrian Gogiids (Eocrinoidea,Echinodermata) from Guizhou Province,China

Gogiid eocrinoids from the Lower Cambrian (Balang Formation — Guizhoueocrinus) and basal Middle Cambrian (Kaili Formation — Sinoeocrinus, Globoeocrinus) in Guizhou Province, China are found in great numbers and are extremely well preserved as high fidelity molds in shale/mud sized siliciclastics. Because of their numbers, complete ontogenetic growth sequences have been observed. Significant differences in growth patterns (heterochrony) are present between Lower and Middle Cambrian genera: thecal plates tend to be paedomorphic in development, while the sutural pores developed between them are peramorphic in their development. Because of the large surface area of theca and brachioles relative to the size of the attachment area, considerable drag in ambient currents would necessitate a strong attachment medium. Anchoring by “biogluing”, possibly by collagen, directly to the substrate or to biodetritus is proposed as the method of attachment.     

Graptolite (Hemichordata,Pterobranchia) preservation and identification in the Cambrian Series 3

Due to inadequate preservation, pterobranchs are often difficult to identify in the fossil record, and a better understanding of preservational modes and diagenetic and metamorphic effects is needed for their recognition. Pterobranch hemichordates are common in Cambrian Stage 5 and younger sedimentary rocks, but are frequently overlooked. Often, pterobranch hemichordate colonies have been considered to be algal remains or hydroids. Re‐examination of Cambrian Burgess Shale algae reveals that the genera Yuknessia and Dalyia can be recognized as putative early representatives of pterobranch hemichordates. Distinct fusellar construction of the individual zooidal tubes and branching of the creeping proximal part of the colonies are found in the morphologically similar rhabdopleurid pterobranch genus Sphenoecium. The erect tubes of Sphenoecium do not branch and can reach a length of several centimetres. The development of the fusellar construction in this taxon shows a highly irregular development of the suture patterns, but a fairly consistent height of the individual fuselli. The taxon is widely distributed in the Cambrian Series 3, but has regularly been identified as a hydroid or an alga. Sphenoecium wheelerensis from the Cambrian Wheeler Shale of Utah is described as new.     

关山生物群中始海百合化石的再研究*

关山生物群是继澄江生物群之后云南寒武纪早期地层中发现的又一个特异埋藏的化石宝库。现已报道10多个门类的化石动物,对研究寒武纪生命大爆发、后生动物起源及演化、寒武纪早期生态系统的复原等重大学术问题具有特殊的意义。始海百合属于棘皮动物门海蕾亚门,于寒武纪早期出现,志留纪灭绝。笔者将荧光显微镜等先进成像方式与传统的研究手段相结合,对新采集到的关山生物群始海百合化石标本进行深入细致的系统古生物学研究,对其精细形态学构造和生活习性获得更深入的了解。这对于认识寒武纪早期的生物多样性和棘皮动物的演化都具有重要的意义。     

Watsonella crosbyi from the lower Cambrian (Terreneuvian,Stage 2) Yanjiahe Formation in Three Gorges Area,South China

Abundant specimens of Watsonella crosbyi are here documented for the first time from the Yanjiahe Formation in Three Gorges area, South China. Specimens were collected from siliceous-phosphatic, intraclastic limestones at the base of Bed 5 in the measured Yanjiahe section, indicating a Cambrian Stage 2 position for Bed 5. The widely used, regional Aldanella yanjiaheensis assemblage zone in Three Gorges area is revised herein as the Watsonella crosbyi zone, allowing for greater accuracy and utility when correlating on a global scale. The examination of microstructures of W. crosbyi further confirms that its shell consists of two layers: an outer prismatic layer and an inner lamello-fibrillar layer with a stepwise texture. A pair of muscle attachment sites below the apex provide new soft part information about Watsonella, confirming that Watsonella is an untorted helcionelloid (mollusc) with endogastrically coiled shell. The stratigraphic range of W. crosbyi in the Yanjiahe Formation correlates with the ranges of the taxon elsewhere in South China as well as in Siberia, Mongolia, Avalonia, Australia and France. Its nearly cosmopolitan distribution and its occurrence across a range of facies and palaeolatitudes reinforce the notion that the FAD of W. crosbyi represents the best candidate for defining the base of Cambrian Stage 2.     

Evolution of C isotopes in the Cambrian of China: implications for Cambrian subdivision and trilobite mass extinctions

Carbon and oxygen isotopes were studied in fossiliferous Cambrian carbonates in northwestern Hunan Province (South China) and in northern Anhui and southern Shandong provinces (North China). Two major C isotope excursions related to biological events occur in the Wangcun section (Yongshun County, northwestern Hunan), which consists of a slope carbonate sequence (510 m thick) containing abundant trilobites. The first C isotope excursion (δ¹³C value shifts from -2.3‰ to 2‰) occurs near the boundary between the Qingxudong and Aoxi formations, close to the traditional Lower-Middle Cambrian boundary. The second excursion (δ¹³C value shifts from 0‰ to 3‰) occurs in the interval between the Linguagnostus reconditus Zone and the Glyptagnostus reticulatus Zone. The base of the G. reticulatus Zone define the base of the Paibi Stage and Furongian Series. Similar C isotope excursions also occur in shallow - water carbonate sections in North China. In Jiagou section near Huainan (Anhui Province), recently considered an important interval for defining the lower-middle Cambrian boundary because of dramatic changes in the trilobite fauna (extinction of redlichiids and appearances of ptychopariids), a negative C isotope excursion (δ¹³C value shifts from +1.21‰ to -1.93‰) occurs at the top of the lower member of the Mantou Formation. In the Gushan section (Changqing County, Shandong Province), a C isotope excursion (δ¹³C value shifts from -0.04‰ to 2.23‰) occurs at the base of the Changshan Formation and is coincident with the base of the Chuangia Zone. This excursion can be correlated with the excursion in the lower part of Glyptagnostus reticulatus Zone in the Wangcun section. The above two distinct C isotope excursions, which occur both in slope carbonates in South China and in shallow - water carbonates in North China, have also been recognized in Cambrian sections on other continents, and they coincide with global mass extinctions of trilobites. The two excursions evidently reflect global changes of Cambrian sea level, and they have utility for Cambrian subdivisions and for both regional and global stratigraphic correlation. In addition, a negative carbon excursion below the base of the Ptychagnostus atavus Zone in the Wangcun section supports previous suggestions that the FAD of P. atavus can be considered as a global correlatable horizon within the middle Cambrian.