Testing the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus

:  The hypothesis that the Ediacara biota were giant protozoans is tested by considering the external morphology, internal organization, suggested fossil representatives and molecular phylogeny of the xenophyophores. From this analysis, we find no case to support a direct relationship. Rather, the x...

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Bibliographic Details
Published in:Palaeontology 2011-09, Vol.54 (5), p.1157-1175
Main Authors: ANTCLIFFE, JONATHAN B., GOODAY, ANDREW J., BRASIER, MARTIN D.
Format: Article
Language:English
Subjects:
development
Ediacara
Ediacara biota
evolution
Foraminifera
Fossils
Hypothesis testing
Palaeopascichnus
Protozoa
xenophyophores
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Summary::  The hypothesis that the Ediacara biota were giant protozoans is tested by considering the external morphology, internal organization, suggested fossil representatives and molecular phylogeny of the xenophyophores. From this analysis, we find no case to support a direct relationship. Rather, the xenophyophores are here regarded as a group of recently evolved Foraminifera and are hence unlikely to have a record from the Ediacaran Period. Further from the growth dynamics of Foraminifera, they are also unlikely to be related to the Palaeopascichnus organism. We also find significant distinctions in the growth dynamics of Palaeopascichnus and organisms usually referred to the Ediacara biota, such as Charnia and Dickinsonia. Developmental analysis of the Palaeopascichnus– central to the xenophyophore hypothesis – reveals unusual, protozoan features, including evidence for chaotic repair structures, for mergence of coeval forms, as well as complex bifurcations. These observations suggest that Palaeopascichnus is a body fossil of an unidentified protozoan but is unrepresentative of Ediacaran body construction, in general.
ISSN:0031-0239
1475-4983
DOI:10.1111/j.1475-4983.2011.01058.x