Using MicroCT Analysis of Ediacaran Fossil Pteridinium simplex

Three-dimensional microCT analysis of the Ediacara fossil Pteridinium simplex sheds new light on its ecology and phylogenetic affinity

Authors:

Meyer et al

Abstract:

Ediacara fossils often exhibit enigmatic taphonomy that complicates morphological characterization and ecological and phylogenetic interpretation; such is the case with Pteridinium simplex from the late Ediacaran Aar Member in southern Namibia. Pteridinium simplex is often preserved as three-dimensional (3D) casts and molds in coarse-grained quartzites, making detailed morphological characterization difficult. In addition, P. simplex is often transported, distorted, and embedded in gutter fills or channel deposits, further obscuring its morphologies. By utilizing microfocus X-ray computed tomography (microCT) techniques, we are able to trace individual specimens and their vanes in order to digitally restore the 3D morphology of this enigmatic fossil. Our analysis shows that P. simplex has a very flexible integument that can be bent, folded, twisted, stretched, and torn, indicating a certain degree of elasticity. In the analyzed specimens, we find no evidence for vane identity change or penetrative growth that were previously used as evidence to support a fully endobenthic lifestyle of P. simplex; instead, evidence is consistent with the traditional interpretation of a semi-endobenthic or epibenthic lifestyle. This interpretation needs to be further tested through microCT analysis of P. simplex specimens preserved in-situ rather than transported ones. The elastic integument of P. simplex is inconsistent with a phylogenetic affinity with xenophyophore protists; instead, its physical property is consistent with the presence of collagen, chitin, and cellulose, an inference that would provide constraints on the phylogenetic affinity of P. simplex.