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  • 1. Huldtgren, Therese
    et al.
    Cunningham, John
    Yin, Chongyu
    Stampanoni, Marco
    ETH Zürich.
    Marone, Federica
    Paul Scherrer Institute.
    Donoghue, Philip C. J.
    University of Bristol.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Fossilized nuclei and germination structures identify Ediacaran ‘animal embryos’ as encysting protists.2011In: Science, ISSN 0036-8075, Vol. 334, no 6063, p. 1696-1699Article in journal (Refereed)
    Abstract [en]

    Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion.

  • 2. Huldtgren, Therese
    et al.
    Cunningham, John
    Yin, Chongyu
    Stampanoni, Marco
    ETH Zürich.
    Marone, Federica
    Paul Scherrer Institute.
    Donoghue, Philip C. J.
    University of Bristol.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Response to comment on “Fossilized nuclei and germination structures identify Ediacaran ‘animal embryos’ as encysting protists”.2012In: Science, ISSN 0036-8075, Vol. 335, no 6073, p. 1169d-Article in journal (Refereed)
    Abstract [en]

    The objections of Xiao et al. to our reinterpretation are based on incorrect assumptions. The lack of nanocrystals lining the nuclear membrane is consistent with membrane fossilization, and nucleus volume through development is correlated to cytoplasm volume and fully consistent with sizes of eukaryote nuclei. Identical envelope structure unites the developmental stages of the fossils, and 2n cleavage and Y-shaped junctions are holozoan symplesiomorphies.

  • 3. Müller, Johannes
    et al.
    Scheyer, Torsten M
    Head, Jason J
    Barrett, Paul M
    Werneburg, Ingmar
    Ericson, Per G P
    Swedish Museum of Natural History, Research Division.
    Pol, Diego
    Sánchez-Villagra, Marcelo R
    Homeotic effects, somitogenesis and the evolution of vertebral numbers in recent and fossil amniotes.2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 5, p. 2118-23Article in journal (Refereed)
    Abstract [en]

    The development of distinct regions in the amniote vertebral column results from somite formation and Hox gene expression, with the adult morphology displaying remarkable variation among lineages. Mammalian regionalization is reportedly very conservative or even constrained, but there has been no study investigating vertebral count variation across Amniota as a whole, undermining attempts to understand the phylogenetic, ecological, and developmental factors affecting vertebral column variation. Here, we show that the mammalian (synapsid) and reptilian lineages show early in their evolutionary histories clear divergences in axial developmental plasticity, in terms of both regionalization and meristic change, with basal synapsids sharing the conserved axial configuration of crown mammals, and basal reptiles demonstrating the plasticity of extant taxa. We conducted a comprehensive survey of presacral vertebral counts across 436 recent and extinct amniote taxa. Vertebral counts were mapped onto a generalized amniote phylogeny as well as individual ingroup trees, and ancestral states were reconstructed by using squared-change parsimony. We also calculated the relationship between presacral and cervical numbers to infer the relative influence of homeotic effects and meristic changes and found no correlation between somitogenesis and Hox-mediated regionalization. Although conservatism in presacral numbers characterized early synapsid lineages, in some cases reptiles and synapsids exhibit the same developmental innovations in response to similar selective pressures. Conversely, increases in body mass are not coupled with meristic or homeotic changes, but mostly occur in concert with postembryonic somatic growth. Our study highlights the importance of fossils in large-scale investigations of evolutionary developmental processes.

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