Abstract
The Weng’an site of exceptional preservation from the 609 Ma Doushantuo Formation of South China provides a unique window on marine diversity prior to the emergence of unequivocal animal fossils, as it dates to the period in which animals are estimated to have emerged based on molecular clock analyses. The biota preserves a variety of forms, including putative animal embryos and putative florideophyte algae, however these fossils have proven difficult to interpret and their affinities remain uncertain.The aims of this thesis were to develop a better understanding of the taphonomy of the various components of the biota and how their taphonomy can elucidate or obscure details of their biology.
I have described a new component of the biota, a spore-producing eukaryote that represents part of a vegetative phase of a developmental cycle, adding to a growing body of evidence that this was a common strategy in Ediacaran acritarchs as a response to the environment in which they lived.
I have undertaken a critical evaluation of the Weng’an algae and their taxonomy and phylogenetic interpretations, and found that several of the algal taxa represent different stages of a single life cycle. Furthermore, the algae of the Weng’an biota are total-group Rhodopyta, and cannot definitively be placed within crown-Florideophyceae, calling into question several molecular divergence time analyses that have used them for calibrations.
Finally, I have evaluated the animal embryo interpretation of the Weng’an embryoids, comparing their taphonomy to that of living embryos and unequivocal fossil embryos with a similar diagenetic history. I found that the differing decay and preservation pathways of embryos at different developmental stages means that an animal interpretation for the Weng’an embryoids cannot be ruled out, despite their preservation being fundamentally different to unequivocal animal embryos in terms of structures preserved.
This thesis adds to evidence that the Weng’an fossils were adapted for variable marine conditions, and shows that those elements of the biota that are widely used as calibrations in molecular divergence time analyses (in particular the embryos and the algae) are used erroneously, as the fossils cannot be definitively placed in the clades whose emergence they are used to date.
| Date of Award | 2 Dec 2021 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Sponsors | Natural Environment Research Council |
| Supervisor | Philip C J Donoghue (Supervisor) & John A Cunningham (Supervisor) |