Nuclei and nucleoli in embryo-like fossils from the Ediacaran Weng’an Biota

Yin, Zongjun; Cunningham, John A.; Vargas, Kelly; Bengtson, Stefan; Zhu, Maoyan; Donoghue, Philip C. J.

doi:10.1016/j.precamres.2017.08.009

Cited by 33 publications

(44 citation statements)

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“…The presence of an outer envelope is potentially difficult to rationalise since it requires that the development of Caveasphaera ( Figure 3C), with a greater than eight-fold increase in volume across specimens in our collection ( Figure 3B), proceeded without an external source of nutrients. This contrasts with the pattern of development exhibited by Tianzhushania and Spiralicellula from the same deposit, which exhibit a more approximately constant volume across a pattern of binary reductive palintomy [3,25]. This could be rationalised in Caveasphaera if the true pattern of development is the reverse of that described in Figure 3C, where the larger, denser specimens represent the earliest stages and development proceeds through the loss of cells, perhaps as propagules or gametes, detaching first from the interior as individual cells and clusters, with the overall cell mass reshaping and resizing through this process.…”

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confidence: 72%

“…Nevertheless, two specimens of Caveasphaera preserve an extracellular matrix containing spheroidal structures that are smaller than the polygonal cells (Figure 4E-H, K, L;Figure S3). These exhibit comparable preservation to the structures interpreted as intracellular lipid droplets in Tianzhushania and Spiralicellula[17,25], suggesting that these developmental stages of Caveasphaera may have been invested in extracellular lipids that sustained growth and development within the closed, enveloped environment.DISCUSSIONThe multicelled organisation of Caveasphaera invites comparison to prokaryotes and eukaryotes with multicellular stages in their life cycles. The branching arrangement of cell masses seen in the cyanobacterium Microcystis [26, 27] are particularly reminiscent of Caveasphaera, but Microcystis does not comprise spheroids in this planktonic conformation [28].…”

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The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology

et al. 2019

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The Ediacaran Weng'an Biota (Doushantuo Formation, 609 million years old) is a rich microfossil assemblage that preserves biological structure to a subcellular level of fidelity and encompasses a range of developmental stages [1]. However, the animal embryo interpretation of the main components of the biota has been the subject of controversy [2, 3]. Here we describe the development of Caveasphaera, which varies in morphology from lensoid, to a hollow spheroidal cage [4], to a solid spheroid [5], but has largely evaded description and interpretation. Caveasphaera is demonstrably cellular and develops within an envelope by cell division and migration, first defining the spheroidal perimeter via anastomosing cell masses that thicken and ingress as strands of cells that detach and subsequently aggregate in the polar region. Concomitantly, the overall diameter increases as does the volume of the cell mass but, after an initial phase of reductive palinotomy, the volume of individual cells remains the same through development. The process of cell ingression, detachment and polar aggregation is analogous to gastrulation; together with evidence of functional cell adhesion and development within an envelope, this is suggestive of a holozoan affinity. Maternal investment in the embryonic development of Caveasphaera and co-occuring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved. RESULTS The Weng'an biota provides a unique insight into multicellular life in the early Ediacaran period during which molecular clocks estimate the fundamental animal lineages to have diverged [6]. Indeed, there are numerous claims of animal remains from the biota, including miniature adult eumetazoans [7] and bilaterians [8], and embryonic animals [2, 9-12], but all remain contentious [3, 13-18]. However, there is a broader diversity of fossil remains from this deposit that have been the subject of little attention, some of which may have a greater claim on animal affinity. These fossils include Caveasphaera costata (Figure 1) which has been described as a spherical hollow cage (Figure 1A-C) [4] to a more solid sphere (Figure 1D) [5] of unknown nature and affinity, though superficial comparison has been drawn to embryos of an octocoral [4]. Analysis of the structure and development of Caveasphaera is challenging because of its small size and complex morphology. We employed Synchrotron Radiation X-ray Tomographic Microscopy (srXTM) [19] and High resolution Xray microtomography [20] to analyse 233 specimens of Caveasphaera that encompass its morphological and size range, based on a rich fossil assemblage from '54' and Datang quarries in the

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The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology

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“…Features known to be preserved through phosphatization include microbes, [78] cells and embryos with possible nuclei, [79] guts, [80] epidermis, [75] and muscles. [46,78,81,82] Experiments have revealed the importance of microbial activity in releasing phosphate and generating the necessary geochemical gradients to induce phosphatization in a decaying carcass.…”

Section: Authigenic Mineralization Saves Tissues Apparently Doomed Tomentioning

confidence: 99%

Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

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Exceptionally preserved fossils are the product of complex interplays of biological and geological processes including burial, autolysis and microbial decay, authigenic mineralization, diagenesis, metamorphism, and finally weathering and exhumation. Determining which tissues are preserved and how biases affect their preservation pathways is important for interpreting fossils in phylogenetic, ecological, and evolutionary frameworks. Although laboratory decay experiments reveal important aspects of fossilization, applying the results directly to the interpretation of exceptionally preserved fossils may overlook the impact of other key processes that remove or preserve morphological information. Investigations of fossils preserving nonbiomineralized tissues suggest that certain structures that are decay resistant (e.g., the notochord) are rarely preserved (even where carbonaceous components survive), and decay-prone structures (e.g., nervous systems) can fossilize, albeit rarely. As we review here, decay resistance is an imperfect indicator of fossilization potential, and a suite of biological and geological processes account for the features preserved in exceptional fossils.

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“…As prokaryotes, they have no nuclei, and cannot produce thick cysts with complex ornaments like Archaeooides and the EAEFs (Xiao et al, 2007). On the contrary, Archaeooides and the EAEFs have been widely accepted as eukaryotes because of their large sizes, complex cysts, multicellular structures, and well-preserved nuclei within cells of many EAEFs (Yin et al, 2017).…”

Section: Evaluation Of Candidate Hypothesesmentioning

confidence: 99%

Early Cambrian animal diapause embryos revealed by X-ray tomography

Yin

Zhao

Pan

et al. 2018

Geology

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Discoveries of animal embryos have profoundly improved our understanding of the early evolution of animal development. However, the fossil record of early animal embryos is extremely sparse. Here we present some three-dimensionally (3-D) phosphatized Archaeooides from the basal Cambrian in southern Shaanxi Province, China. The 3-D reconstructions of a number of specimens, aided by high-resolution X-ray tomography, demonstrate that these soft-bodied fossil organisms have a thick cyst characterized by pustule-like ornaments and vesicular structures. Furthermore, a multicellular inner body undergoing palintomic cell division is enclosed by the cyst. The suite of characters, including submillimeter to millimeter scale, a palintomic pattern of cell division, and a complex cyst wall microstructure, corroborate the hypothesis that Archaeooides fossils represent the embryonic remains of animals. More specifically, the structure of the cyst wall bears close comparison to the resting cysts of living invertebrates, allowing us to interpret Archaeooides as a diapause embryonic stage adapted to the temporally and spatially heterogeneous redox conditions that extended from the Ediacaran to the early Cambrian. The global distribution of Archaeooides indicates that these conditions were geographically widespread. Ultimately, Archaeooides provides evidence of the early evolution of this metazoan life history strategy as an adaptation to adverse environmental conditions. Its widespread occurrence in both conventional and exceptional taphonomic windows provides the potential for reconstructing its embryology and, by inference, the developmental evolution of early animals and their body plans.

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Nuclei and nucleoli in embryo-like fossils from the Ediacaran Weng’an Biota

Cited by 33 publications

References 35 publications

The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology

The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology

Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

Early Cambrian animal diapause embryos revealed by X-ray tomography

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