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. 2014 Sep 9;111(36):13122-6.
doi: 10.1073/pnas.1408542111. Epub 2014 Aug 11.

Fractal branching organizations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan

Jennifer F Hoyal Cuthill  1 , Simon Conway Morris  2
Affiliations

Fractal branching organizations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan

Jennifer F Hoyal Cuthill et al. Proc Natl Acad Sci U S A. .

Abstract

The branching morphology of Ediacaran rangeomorph fronds has no exact counterpart in other complex macroorganisms. As such, these fossils pose major questions as to growth patterns, functional morphology, modes of feeding, and adaptive optimality. Here, using parametric Lindenmayer systems, a formal model of rangeomorph morphologies reveals a fractal body plan characterized by self-similar, axial, apical, alternate branching. Consequent morphological reconstruction for 11 taxa demonstrates an adaptive radiation based on 3D space-filling strategies. The fractal body plan of rangeomorphs is shown to maximize surface area, consistent with diffusive nutrient uptake from the water column (osmotrophy). The enigmas of rangeomorph morphology, evolution, and extinction are resolved by the realization that they were adaptively optimized for unique ecological and geochemical conditions in the late Proterozoic. Changes in ocean conditions associated with the Cambrian explosion sealed their fate.

Keywords: paleobiology; paleontology.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Schematic L-system model of Beothukis mistakensis. (A) First three steps of the branching process. (B) Final morphology at step 38. Segment colors indicate relative age, from oldest (red) to youngest (light blue). Numbers indicate branch order (0, stem; 1, primary; 2, secondary; 3, tertiary; and 4, quaternary).
Fig. 2.
Fig. 2.
Ediacaran rangeomorph fossils and their 3D L-system models. (A and B) Avalofractus abaculus. A reproduced with permission from ref. , figure 3.1. (C and D) Charnia masoni. (C) South Australia Museum specimen number P36574, described in ref. , image courtesy of Jim Gehling (South Australian Museum, Adelaide, Australia). (Scale bars, 1 cm.)
Fig. 3.
Fig. 3.
Three-dimensional space-filling by Ediacaran rangeomorph fronds (illustrated 1/2 estimated life size). Locations indicate estimated bounding box size in inferred life orientation (values in SI Appendix, Table S2). Frond colors indicate Euclidean distance-based clusters (cophenetic correlation coefficient = 0.77).
See this image and copyright information in PMC

Comment in

References

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