Guoxiang Li

Basal Cambrian Microfossils from the Yangtze Gorges Area (South China) and the Aksu Area (Tarim Block, Northwestern China)

Abstract The basal Cambrian marks the beginning of an important chapter in the history of life. However, most paleontological work on the basal Cambrian has been focused on skeletal animal fossils, and our knowledge about the primary producers—cyanobacteria and eukaryotic phytoplankton (e.g., acritarchs)—is limited. In this research, we have investigated basal Cambrian acritarchs, coccoidal microfossils, and cyanobacteria preserved in phosphorites and cherts of the Yanjiahe Formation in the Yangtze Gorges area (South China) and the Yurtus Formation in the Aksu area (Tarim Block, northwestern China). Our study confirms the occurrence in these two formations of small acanthomorphic acritarchs characteristic of the basal Cambrian Asteridium–Comasphaeridium–Heliosphaeridium (ACH) assemblage. These acritarchs include abundant Heliosphaeridium ampliatum (Wang, 1985) Yao et al., 2005, common Yurtusia uniformis n. gen. and n. sp., and rare Comasphaeridium annulare (Wang, 1985) Yao et al., 2005. In addition, these basal Cambrian successions also contain the clustered coccoidal microfossil Archaeophycus yunnanensis (Song in Luo et al., 1982) n. comb., several filamentous cyanobacteria [Cyanonema majus n. sp., Oscillatoriopsis longa Timofeev and Hermann, 1979, and Siphonophycus robustum (Schopf, 1968) Knoll et al., 1991], and the tabulate tubular microfossil Megathrix longus L. Yin, 1987a, n. emend. Some of these taxa (e.g., H. ampliatum, C. annulare, and M. longus) have a wide geographic distribution but occur exclusively in basal Cambrian successions, supporting their biostratigraphic importance. Comparison between the stratigraphic occurrences of microfossils reported here and skeletal animal fossils published by others suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.

Early Cambrian lingulate brachiopods from the Shaanxi Province, China

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

Early Cambrian pentamerous cubozoan embryos from South China.

Background Extant cubozoans are voracious predators characterized by their square shape, four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian; by that time probably all representatives of the living marine phyla, especially those of basal animals, should have evolved. Methods Microscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos, each of which bears five pairs of subumbrellar tentacle buds, were analyzed in detail through computed microtomography (Micro-CT) and scanning electron microscopy (SEM) without coating. Results The figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry, allowing detailed comparison with modern cnidarians, especially medusozoans. A combination of features, such as the claustrum, gonad-lamella, suspensorium and velarium suspended by the frenula, occur exclusively in the gastrovascular system of extant cubozoans, indicating a cubozoan affinity for these fossils. Additionally, the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans, implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with extant pelagic juvenile cubomedusae rather than sessile cubopolyps, whcih indicates a direct development in these fossil taxa, lacking characteristic stages of a typical cnidarian metagenesis such as planktonic planula and sessile polyps.

A sclerite-bearing stem group entoproct from the early Cambrian and its implications

The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans.

An early Cambrian agglutinated tubular lophophorate with brachiopod characters

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long pedicle with coelomic space. The terminal bulb of the pedicle provided anchorage in soft sediment. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.

Lower Cambrian small shelly faunas from Zhejiang (China) and their biostratigraphical implications

Abstract Despite a long history of research on the Early Cambrian in China most available data on small skeletal fossils concern fossil associations of the shallow carbonate platform. Information on skeletal fossils from marginal shelf environments of the Yangtze Platform is scanty, which may reflect the rarity of fossils in deeper sedimentary environments but is also due to limitation of carbonate distribution and outcrops, difficulties in fossil extraction, and a general research focus on the Precambrian—Cambrian boundary beds on the carbonate platform. Here we present a documentation of Meishucunian to Qiongzhusian smallskeletal fossils from the lower Hetang Formation and the chert unit at its base from the Jiangshan region, Zhejiang Province, representing a relatively deep shelf environment compared to the inner shelfregion. The earliest association (Meishucunian) from the chert unit underlying the Hetang Formation is mainly characterized by the occurrence of Protohertzina anabarica, P. unguliformis, ...

New C isotope stratigraphy from southwest China: Implications for the placement of the Precambrian- Cambrian boundary on the Yangtze Platform and global correlations: Comment and Reply

Shen and Schidlowski (2000) present a C isotope profile from thePrecambrian-Cambrian (PC-C) interval in east Yunnan for the placementof the PC-C boundary on the Yangtze Platform and for global correlation.We here challenge Shen and Schidlowski’s (2000) chemostratigraphic cor-relation and point out important omissions and biostratigraphic errors intheir paper.Omissions. Shen and Schidlowski (2000, p. 623) state that ‘‘no dis-tinct shift has yet been reported for the isotope composition of carbonacross the China marker A.’’ However, the authors fail to take into accountthe work of Brasier et al. (1990, and references therein), who report anegative

Skeletal faunas from the Qiongzhusian of southern Shaanxi: Biodiversity and lithofacies-biofacies links in the Lower Cambrian carbonate settings

Abstract The Xiaoyang section, located in Zhenba County of Shaanxi Province, is important both for documenting the biodiversity of the Qiongzhusian Stage (Lower Cambrian) and for analyzing lithofacies-biofacies links in carbonate depositing environments on the Yangtze Platform. The skeletal fossils from the Xihaoping Member, including linguloid valves, cambroclavid and chancelloriid sclerites, genal and occipital spines of polymerid trilobites, and tubular fossils, are described here as the Eoobolus-Cambroclavus fauna, which mainly occurred in peritidal environments. The fossils from the argillaceous limestones of the lower Shuijingtuo Formation, containing Ungulate brachiopods eodiscoid trilobites, bivalved arthropods, microdictyoniid sclerites and siliceous sponge spicules, are regarded as the Palaeobolus-Mupeidiscus-Kunmingella fauna, which presumably lived in subtidal or deeper water environments. The faunal diversity in the Xihaoping Member is lower than that in the lower Shuijingtuo Formation. The i...

Cambrothyra ampulliformis, An Unusual Coeloscleritophoran from the Lower Cambrian of Shaanxi Province, China

Abstract Cambrothyra ampulliformis Qian and Zhang, 1983, is a jar- or vase-shaped fossil known from the Lower Cambrian of Shaanxi and Hubei provinces, China. It has been interpreted as a protistan test or cyst or a metazoan sclerite. A large collection of specimens from the Xihaoping Member of the Dengying Formation in southern Shaanxi Province permits its detailed redescription. These fossils are highly variable in shape but this variation is continuous and does not support the current recognition of multiple species for this material. They were originally hollow with a restricted basal foramen and a calcareous wall probably composed of fibrous aragonite. All of these features support the identification of Cambrothyra as sclerites of a coeloscleritophoran, a problematic group of Cambrian scleritome-bearing metazoans. Furthermore, the walls of Cambrothyra sclerites contain numerous pores, a feature shared with other coeloscleritophorans. Cambrothyra resembles chancelloriids in particular due to the shared presence of a verruculose texture around the foramen and the absence of mirror-image pairs of asymmetric sclerites. However, unlike chancelloriids, which have rosette-like compound sclerites, the scleritome of Cambrothyra was dominated by isolated sclerites, with only a few pairs and clusters of sclerites and twin sclerites. Consequently, we hypothesize that Cambrothyra forms a clade with other chancelloriids, but represents a basal lineage that plesiomorphically retained isolated sclerites. The morphology of Cambrothyra sclerites, which shares features with both chancelloriids and halkieriids, thus supports the hypothesis that all coeloscleritophorans form a natural group.

New occurrence of Cambroclavus absonus from the lowermost Cambrian of North China and its stratigraphical importance

Li, L.-Y., Zhang, X.-L., Yun, H. & Li, G.-X., October 2015. New occurrence of Cambroclavus absonus from the lowermost Cambrian of North China and its stratigraphical importance. Alcheringa 40, xxx–xxx. ISSN 0311-5518. The problematic Small Shelly Fossil Cambroclavus absonus is described from the Xinji Formation in the Longxian area, which is located near the southwestern margin of the North China Platform. The Xinji Formation, the basal rock unit of the Cambrian in the studied area, yields an assemblage of skeletal fossils that share many common elements with contemporary faunas from South Australia. Sclerites of C. absonus reported herein represent the first occurrence of the species outside Australia, thus extending the palaeogeographic range of the taxon to northern China. To date, palaeogeographic occurrences of Cambroclavus sclerites are restricted to the Peri-Gondwana realm, including South China, Australia, Tarim, Kazakhstan, North China and Western Europe. These occurrences are divided into a Southern Group realm and Northern Group realm. Stratigraphically, Cambroclavus occurs mostly in Cambrian Stage 3 and has three occurrences in Stage 5, separated by Stage 4 in which Cambroclavus has not yet been found. The first appearance datum of Cambroclavus in Cambrian Stage 3 is of importance for regional and inter-regional correlations. In particular, the presence of Cambroclavus absonus in North China allows species-level correlation between North China and South Australia. Luoyang Li [lly@stumail.nwu.edu.cn], Xingliang Zhang [xzhang69@nwu.edu.cn], Hao Yun [yunhao@stumail.nwu.edu.cn], Early Life Institute and State Key Laboratory Of Continental Dynamics, Department of Geology, Northwest University, Xian 710069, PR China; Guoxiang Li [gxli@nigpas.ac.cn], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China.