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Constructional and functional morphology of Ediacaran rangeomorphs

Published version
Peer-reviewed

Type

Article

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Authors

Butterfield, Nicholas  ORCID logo  https://orcid.org/0000-0002-3046-7520

Abstract

Ediacaran rangeomorphs were the first substantially macroscopic organisms to appear in the fossil record, but their underlying biology remains problematic. Although demonstrably heterotrophic, their current interpretation as osmotrophic consumers of dissolved organic carbon (DOC) is incompatible with the inertial (> Re) and advective (> Pe) fluid-dynamics accompanying macroscopic length-scales. The key to resolving rangeomorph feeding and physiology lies in their underlying construction. Taphonomic analysis of three-dimensionally preserved Charnia from the White Sea identifies the presence of large, originally water-filled compartments that served both as a hydrostatic exoskeleton and semi-isolated digestion chambers capable of processing recalcitrant substrates – likely in conjunction with a resident microbiome. At the same time, the hydrodynamically exposed outer surface of macroscopic rangeomorphs would have dramatically enhanced both gas exchange and food delivery. A bag-like epithelium filled with transiently circulated seawater offers an exceptionally efficient means of constructing a simple, DOC-consuming, multicellular heterotroph. Such a bodyplan is broadly comparable to that of anthozoan cnidarians – minus such derived features as muscle, tentacles and a centralized mouth. Along with other early bag-like fossils, rangeomorphs can be reliably identified as total-group eumetazoans, potentially colonial stem-group cnidarians.

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Journal Title

Geological Magazine

Conference Name

Journal ISSN

0016-7568

Volume Title

Publisher

Cambridge University Press
Sponsorship
Natural Environment Research Council (NE/P002412/1)
NERC