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First non-destructive internal imaging of Rangea, an icon of complex Ediacaran life

Sharp, AC; Evans, AR; Wilson, SA; Vickers-Rich, P; (2017) First non-destructive internal imaging of Rangea, an icon of complex Ediacaran life. Precambrian Research , 299 pp. 303-308. 10.1016/j.precamres.2017.07.023. Green open access

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Abstract

The origins of multicellular life have remained enigmatic due to the paucity of high-quality, three-dimensionally preserved fossils. Rangea was a centimetre- to decimetre-scale frond characterised by a repetitive pattern of self-similar branches and a sessile benthic lifestyle. Fossils are typically preserved as moulds and casts exposing only a leafy petalodium, and the rarity and incompleteness of specimens has made it difficult to reconstruct the three-dimensional (3D) morphology of the entire organism. This, in turn, has led to many differing interpretations of its morphology and phylogenetic affinities. Here we use high resolution X-ray micro-computed tomography (microCT) to investigate the 3D internal morphology of rare, exceptionally preserved ironstone fossils of Rangea from the Nama Group in southern Namibia. Our investigation reveals a series of structures that represent boundaries between individual fronds or structural elements that divide into smaller secondary and tertiary elements, leading to a repetitive pattern of branches. These elements surround an internal core of a distinctly different texture and internal appearance. There is no distortion of the walls of the primary elements, thus we conclude that Rangea likely had a rigid or semi-rigid skeleton-like structure that prevented buckling or compression and maintained integrity during life. We compare these findings with previous interpretations of Rangea morphology and present new insights on the architecture of internal structures, such as the central core, and the overall appearance of this complex Ediacaran life form. Our insights based on microCT scans of these rare, uniquely-preserved specimens provide a more accurate interpretation of the 3D morphology essential for determining the true affinities and modes of life of the Ediacaran biota during this early stage in the evolution of complex macroscopic life.

Type: Article
Title: First non-destructive internal imaging of Rangea, an icon of complex Ediacaran life
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.precamres.2017.07.023
Publisher version: http://doi.org/10.1016/j.precamres.2017.07.023
Language: English
Additional information: © 2017 Elsevier B.V. All rights reserved. This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Ediacaran; Precambrian; Computed tomography; Rangea; Aar Member; Namibia
URI: http://discovery.ucl.ac.uk/id/eprint/10044253
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