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Reconstructing the reproductive mode of an Ediacaran macro-organism

Nature volume 524, pages 343–346 (2015)Cite this article

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Abstract

Enigmatic macrofossils of late Ediacaran age (580–541 million years ago) provide the oldest known record of diverse complex organisms on Earth, lying between the microbially dominated ecosystems of the Proterozoic and the Cambrian emergence of the modern biosphere1. Among the oldest and most enigmatic of these macrofossils are the Rangeomorpha, a group characterized by modular, self-similar branching and a sessile benthic habit2,3,4. Localized occurrences of large in situ fossilized rangeomorph populations allow fundamental aspects of their biology to be resolved using spatial point process techniques5. Here we use such techniques to identify recurrent clustering patterns in the rangeomorph Fractofusus, revealing a complex life history of multigenerational, stolon-like asexual reproduction, interspersed with dispersal by waterborne propagules. Ecologically, such a habit would have allowed both for the rapid colonization of a localized area and for transport to new, previously uncolonized areas. The capacity of Fractofusus to derive adult morphology by two distinct reproductive modes documents the sophistication of its underlying developmental biology.

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Figure 1: Fractofusus specimens from Newfoundland, Canada.
Figure 2: PCF for mapped taxa.
Figure 3: Isotropy plots from the H14 surface for each size-class of Fractofusus, providing a visualization of specimen positions relative to one another.
Figure 4: Schematic diagram showing simplified Fractofusus spatial arrangements.

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Acknowledgements

The Parks and Natural Areas Division, Department of Environment and Conservation, Government of Newfoundland and Labrador, provided permits to conduct research within the Mistaken Point Ecological Reserve in 2010, while the Department of Tourism, Culture and Recreation provided permits for palaeontological research on the Bonavista Peninsula in 2012. Access to both of the aforementioned fossil localities is by scientific research permit only. Contact the relevant Department listed above for further information. This work has been supported by the Natural Environment Research Council (grant numbers NE/I005927/1 to C.G.K., NE/J5000045/1 to J.J.M., NE/L011409/1 to A.G.L. and NE/G523539/1 to E.G.M.), and a Henslow Junior Research Fellowship from the Cambridge Philosophical Society to A.G.L. We thank M. Laflamme for discussions on this manuscript.

Author information

Authors and Affiliations

  1. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK

    Emily G. Mitchell, Charlotte G. Kenchington & Nicholas J. Butterfield

  2. British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

    Charlotte G. Kenchington

  3. School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol, BS8 1TQ, UK

    Alexander G. Liu

  4. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, UK

    Jack J. Matthews

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Contributions

E.G.M. conceived the project, collected data on the ‘D’ and ‘E’ surfaces and ran the analyses. C.G.K., A.G.L. and J.J.M. collected data on the H14 surface. All authors discussed the results and prepared the manuscript.

Corresponding author

Correspondence to Emily G. Mitchell.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Map and simplified stratigraphic column showing the position of studied bedding planes with bedding plane maps of Fractofusus.

a, Newfoundland, eastern Canada. Dashed area indicates region of interest in b. b, The Avalon and Bonavista Peninsulas, eastern Newfoundland. Locations of the bedding planes are indicated. c, Stratigraphic column (not to scale) compiled of information from the Avalon and Bonavista Peninsulas; lithological units in each region are treated as correlative in this study, but work is continuing to determine the validity of this assumption. The ‘E’ surface at Mistaken Point has been dated to 565 ± 3 Ma (ref. 12). There are currently no available radiometric dates from the Bonavista Peninsula. d–f, Maps of Fractofusus positions on the ‘D’ surface (d), the ‘E’ surface (e) and the H14 surface (f). In e the largest specimens are in light blue, medium specimens in mid-blue and smallest specimens in dark blue.

Extended Data Figure 2 Retrodeformation calculations on the Mistaken Point surfaces.

a, b, Plots of the lengths versus widths of discs from the ‘D’ surface, Mistaken Point (a), and the ‘E’ surface, Mistaken Point (b). The gradient of the line defines the retrodeformation factor, which for the ‘D’ surface is 1.35 ± 0.11 (R2 = 0.92) and for the ‘E’ surface is 1.71 ± 0.08 (R2 = 0.75). c, Fractofusus PCF on the ‘E’ surface with (solid line) and without (dashed line) retrodeformation. The grey shaded area depicts the boundary of 99 Monte Carlo simulations for the model which provided the best-fit model to the retrodeformed data, which has a good fit on the non-retrodeformed data (pd = 0.60).

Source data

Extended Data Figure 3 Size distribution analysis of Fractofusus for the H14 surface.

a, Size–frequency distributions for Fractofusus, (n = 1,214); b, the results of the Bayesian information criterion52,53 (univariate data). Squares and triangles correspond to models assuming equal and unequal variance, respectively. High values of the Bayesian information criterion correspond to a good model fit, so the best-fit model is a three-component equal variance model using log-normalized length data. c–e, Rose diagrams plotting the directional orientation of the different size-classes of Fractofusus on the H14 surface showing large size-class (<11.0 cm, n = 350) (c), intermediate size-class (5.5–11.0 cm, n = 310) (d) and small size-class (<5.5 cm, n = 554) (e). The angles of the Fractofusus central axis are relative to north (0°). There is no strong orientation preference for any of the size-classes.

Source data

Extended Data Figure 4 Distance measures for the size data from H14 surface.

For all plots, the x axis is the inter-point distance between organisms (in metres). a, Mark correlation function5, where 1 corresponds to a lack of correlation of size, such that Fractofusus size is independent and identically distributed. A value of <1 corresponds to a positive dependency (in contrast to PCF) and >1 corresponds to a negative dependency. Small Fractofusus on the H14 surface (<0.3 cm) are more likely to be found near each other than expected by random. b, The ‘E’ surface PCF (solid line) showing the model that fits the data best, a double Thomas cluster model (dotted line, pd = 0.56), and the simulation envelope for 99 Monte Carlo simulations (grey shaded area). c, d, PCF for the best-fit models for the bivariate size-classes of Fractofusus on the H14 surface showing LCMs for small with medium size-classes (pd = 0.74) (c) and LCMs for medium with large size-classes (pd = 0.66) (d). e, The PCF of the largest size-class of H14 (solid line), showing the CSR Monte Carlo simulation envelope in grey, with the ‘D’ surface PCF (dotted line, pd = 0.56). f, Nearest neighbour distances (solid line, pd = 0.01) with CSR Monte Carlo simulation envelope in grey.

Source data

Extended Data Figure 5 Artistic reconstruction of Fractofusus on the H14 surface, Bonavista Peninsula.

The bottom right features a large Fractofusus around which there are five to eight medium specimens clustered. Each of the medium specimens also has small specimens clustered around them. The small specimens therefore form an independent double cluster pattern, namely clusters of clusters. Artwork by C.G.K.

Extended Data Table 1 Best-fit univariate cluster models
Full size table
Extended Data Table 2 Best-fit univariate double cluster models
Full size table
Extended Data Table 3 Best-fit double Thomas cluster models fitted onto other taxa
Full size table
Extended Data Table 4 Best-fit univariate cluster models on heterogeneous backgrounds for ‘E’ surface taxa
Full size table
Extended Data Table 5 Models for bivariate analysis between different size-classes of Fractofusus on the H14 surface
Full size table

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Mitchell, E., Kenchington, C., Liu, A. et al. Reconstructing the reproductive mode of an Ediacaran macro-organism. Nature 524, 343–346 (2015). https://doi.org/10.1038/nature14646

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