Browsing by Author "Xiao, S."

Now showing 1 - 11 of 11
  • Thumbnail Image
  • Thumbnail Image
    Armored kinorhynch-like scalidophoran animals from the early Cambrian.
    Zhang, H.; Xiao, S.; Liu, Y.; Yuan, X.; Wan, B.; Muscente, A. D.; Shao, T.; Gong, H.; Cao, G. (2015-11-26)
    Morphology-based phylogenetic analyses support the monophyly of the Scalidophora (Kinorhyncha, Loricifera, Priapulida) and Nematoida (Nematoda, Nematomorpha), together constituting the monophyletic Cycloneuralia that is the sister group of the Panarthropoda. Kinorhynchs are unique among living cycloneuralians in having a segmented body with repeated cuticular plates, longitudinal muscles, dorsoventral muscles, and ganglia. Molecular clock estimates suggest that kinorhynchs may have diverged in the Ediacaran Period. Remarkably, no kinorhynch fossils have been discovered, in sharp contrast to priapulids and loriciferans that are represented by numerous Cambrian fossils. Here we describe several early Cambrian (~535 million years old) kinorhynch-like fossils, including the new species Eokinorhynchus rarus and two unnamed but related forms. E. rarus has characteristic scalidophoran features, including an introvert with pentaradially arranged hollow scalids. Its trunk bears at least 20 annuli each consisting of numerous small rectangular plates, and is armored with five pairs of large and bilaterally placed sclerites. Its trunk annuli are reminiscent of the epidermis segments of kinorhynchs. A phylogenetic analysis resolves E. rarus as a stem-group kinorhynch. Thus, the fossil record confirms that all three scalidophoran phyla diverged no later than the Cambrian Period.
  • Thumbnail Image
    Carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the Ediacaran Doushantuo Formation
    Qu, Y.; Wang, J.; Xiao, S.; Whitehouse, M.; Engdahl, A.; Wang, G.; McLoughlin, N. (2017-03)
  • Thumbnail Image
    Cryogenian evolution of stigmasteroid biosynthesis
    Hoshino, Y.; Poshibaeva, A.; Meredith, W.; Snape, C.; Poshibaev, V.; Versteegh, G. J. M.; Kuznetsov, N.; Leider, A.; van Maldegem, L.; Neumann, M.; Naeher, S.; Moczydlowska, M.; Brocks, J. J.; Jarrett, A. J. M.; Tang, Q.; Xiao, S.; McKirdy, D.; Das, S. K.; Alvaro, J. J.; Sansjofre, P.; Hallmann, C. (Amer Assoc Advancement Science, 2017-09-01)
  • Thumbnail Image
    Exceptionally preserved fossil assemblages through geologic time and space
    Muscente, A. D.; Schiffbauer, J. D.; Broce, J.; Laflamme, M.; O'Donnell, K.; Boag, T. H.; Meyer, M.; Hawkins, A. D.; Huntley, J. W.; McNamara, M.; MacKenzie, L. A.; Stanley, G. D.; Hinman, N. W.; Hofmann, M. H.; Xiao, S. (2017-08)
  • Thumbnail Image
    Molar tooth carbonates and benthic methane fluxes in Proterozoic oceans.
    Shen, B.; Dong, L.; Xiao, S.; Lang, X.; Huang, K.; Peng, Y.; Zhou, C.; Ke, S.; Liu, P. (2016-01-07)
    Molar tooth structures are ptygmatically folded and microspar-filled structures common in early- and mid-Proterozoic (∼2,500-750 million years ago, Ma) subtidal successions, but extremely rare in rocks <750 Ma. Here, on the basis of Mg and S isotopes, we show that molar tooth structures may have formed within sediments where microbial sulphate reduction and methanogenesis converged. The convergence was driven by the abundant production of methyl sulphides (dimethyl sulphide and methanethiol) in euxinic or H2S-rich seawaters that were widespread in Proterozoic continental margins. In this convergence zone, methyl sulphides served as a non-competitive substrate supporting methane generation and methanethiol inhibited anaerobic oxidation of methane, resulting in the buildup of CH4, formation of degassing cracks in sediments and an increase in the benthic methane flux from sediments. Precipitation of crack-filling microspar was driven by methanogenesis-related alkalinity accumulation. Deep ocean ventilation and oxygenation around 750 Ma brought molar tooth structures to an end.
  • Thumbnail Image
    New Ediacara fossils preserved in marine limestone and their ecological implications
    Chen, Z.; Zhou, C.; Xiao, S.; Wang, W.; Guan, C.; Hua, H.; Yuan, X. (Nature Publishing Group, 2014-02-25)
    Ediacara fossils are central to our understanding of animal evolution on the eve of the Cambrian explosion, because some of them likely represent stem-group marine animals. However, some of the iconic Ediacara fossils have also been interpreted as terrestrial lichens or microbial colonies. Our ability to test these hypotheses is limited by a taphonomic bias that most Ediacara fossils are preserved in sandstones and siltstones. Here we report several iconic Ediacara fossils and an annulated tubular fossil (reconstructed as an erect epibenthic organism with uniserial arranged modular units), from marine limestone of the 551-541 Ma Dengying Formation in South China. These fossils significantly expand the ecological ranges of several key Ediacara taxa and support that they are marine organisms rather than terrestrial lichens or microbial colonies. Their close association with abundant bilaterian burrows also indicates that they could tolerate and may have survived moderate levels of bioturbation.
  • Thumbnail Image
    A new SIMS zircon U-Pb date from the Ediacaran Doushantuo Formation: age constraint on the Weng'an biota
    Zhou, C.; Li, X.-H.; Xiao, S.; Lan, Z.; Ouyang, Q.; Guan, C.; Chen, Z. (Cambridge University Press, 2017-11-01)
    As a well-known phosphatized Lagerstätte, the Ediacaran Weng'an biota in central Guizhou Province of South China contains diverse acanthomorphic acritarchs, algal thalli, tubular microfossils as well as various spheroidal fossils. These fossils provide crucial palaeontological evidence for the radiation of multicellular eukaryotes after the termination of the Neoproterozoic global glaciation. While the Weng'an biota is generally considered as early Ediacaran in age on the basis of phosphorite Pb–Pb isochron ages ranging from 572 Ma to 599 Ma, the reliability and accuracy of these age data have been questioned and some geologists have proposed that the Weng'an biota may be younger than 580 Ma instead. Here we report a SIMS zircon U–Pb age of 609 ± 5 Ma for a tuffaceous bed immediately above the upper phosphorite unit in the Doushantuo Formation at Zhangcunping, Yichang, South China. Litho-, bio- and chemostratigraphic correlations suggest that the upper phosphorite unit at Zhangcunping can be well correlated with the upper phosphorite unit at Weng'an, which is the main horizon of the Weng'an biota. We therefore conclude that the Weng'an biota could be as old as 609 ± 5 Ma.
  • Thumbnail Image
    Recent advances in understanding the terminal Ediacaran Earth-life system in South China and Arctic Siberia
    Cui, H.; Kaufman, Alan J.; Xiao, S.; Grazhdankin, D. V.; Peek, S.; Martin, A. J.; Bykova, N. V.; Rogov, V. I.; Liu, X. M.; Zhang, F.; Romaniello, S. J.; Anbar, A. D.; Peng, Y.; Cai, Y.; Schiffbauer, J. D.; Meyer, M.; Gilleaudeau, Geoffrey J.; Plummer, Rebecca E.; Sievers, N. E.; Goderis, S.; Claeys, P. (2019-11-22)
    The terminal Ediacaran contains dramatic changes in biogeochemical cycles, many of which are closely coupled with evolutionary transitions in the corresponding fossil records. Dynamic redox conditions may have caused a profound impact on early animal evolution. Our work highlights the significance of integrated bio-, litho-, and chemo-stratigraphy in geobiology research of the deep time.
  • Thumbnail Image
  • Thumbnail Image
    A vanished history of skeletonization in Cambrian comb jellies
    Ou, Q.; Xiao, S.; Han, J.; Sun, G.; Zhang, F.; Zhang, Z.; Shu, D. (2015-07)
    Ctenophores are traditionally regarded as "lower" metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for example, an octamerous symmetry, oral-aboral axis, aboral sense organ, and octaradially arranged ctene rows). Unlike most modern counterparts, however, they lack tentacles, have a sclerotized framework, and have eight pairs of ctene rows. They are resolved as a monophyletic group (Scleroctenophora new class) within the ctenophores. This clade reveals a cryptic history and sheds new light on the early evolution of this basal animal phylum. Skeletonization also occurs in some other Cambrian animal groups whose extant members are exclusively soft-bodied, suggesting the ecological importance of skeletonization in the Cambrian explosion.