The evolution of symmetry and the radiation of the first complex macroscopic life

Key Questions

What governs the evolution of organismal symmetry states: phylogeny or ecology?

Background

Body symmetries define most animal lineages: bilaterians are characterised by their shared bilateral appearance; ctenophores all possess biradial symmetry; different cnidarian clades are defined respectively by tetraradial, hexaradial or bilateral symmetry, and sponges are defined by their lack of body symmetry. This suggests that symmetry is conserved over timescales of hundreds of millions of years. However, for many of these groups, the fossil record tells a story of higher variability in symmetry states deep in their evolutionary past. Ascertaining at what point these symmetry states became phylogenetically fixed and why they did so is a prevailing question in evolutionary biology and palaeontology. Ediacaran (~635 – 539 Ma) macrofossils appear suddenly in the fossil record ~570 million years ago and record a variety of strange and unfamiliar frondose and quilted anatomies - sometimes called ‘lost bodyplans’ - which record huge variability in symmetry states. Increasing evidence suggests that a number of these fossils are likely to represent the remains of ancient animals, and so understanding the evolution of symmetry within these groups may help us address the drivers of symmetry evolution – and fixation – through geological time. This project will focus on the evolutionary dynamics of two iconic Ediacaran groups: Rangeomorpha and Erniettomorpha.

Aims of the Project

1) To characterise the variability of symmetry states within rangeomorphs and erniettomorphs.

2) To use computational fluid dynamics to understand the effects of symmetry on feeding and respiration in rangeomorphs and erniettomorphs.

3) To study existing material/datasets as well as collect your own new field data to produce phylogenetic hypotheses for relationships within your study groups.

4) To compare the distribution of different symmetries with palaeoenvironmental variables.

5) To assess the relative roles of phylogeny and ecology on the evolution of symmetry in rangeomorphs and erniettomorphs via a study of phyloecospace occupation through time.

Project Description

Rangeomorpha are a clade of sessile, benthic frondose organisms that are most commonly, although not exclusively, found in deep-water rangeomorph forests. They are among the oldest of the Ediacaran macrofossil groups and are the most diverse, with their radiation being preserved in stratigraphic sections across the UK and Newfoundland, Canada. Rangeomorphs present a variety of different symmetry states, both at the organismal scale and at the scale of various branching orders. Erniettomorpha - a clade of sessile, benthic, bag or frond-like organisms – on the other hand, appear in the youngest Ediacaran deposits of Namibia, recording higher energy, shallow-water palaeoenvironments. Historical difficulties with taxonomy have meant that measures of diversity in erniettomorphs are lacking, but it is clear that there are at least three distinct body-plans, again, all displaying different body symmetries. Rangeomorphs and erniettomorphs therefore have the capacity to inform debate on the evolution of symmetry more broadly – a fundamental, but underexplored body constructional property – and the relative influence of phylogeny (shared evolutionary history) versus ecology (shared habitat). However, surprisingly, symmetry in these late Ediacaran groups has never been studied in detail. Emerging phylogenetic, stratigraphic and palaeoecological datasets would also allow for further studies of Ediacaran macroevolutionary dynamics dealing with, for example, the nature of the radiation of these groups. In order to address these questions, the student will undertake fieldwork in Newfoundland, Canada and in Namibia to collect morphological data on rangeomorphs and erniettomorphs. The student will characterise symmetry states in rangeomorph and erniettomorph taxa and be trained in state-of-the-art techniques in computational fluid dynamics to understand the impact of symmetry on feeding and respiration in different organisms and evaluate their functional performance. The student will also receive training in morphological phylogenetics and macroevolutionary analyses as they seek to expand current datasets such that they represent emerging diversity and disparity in late Neoproterozoic oceans. Finally, the student will collate and integrate palaeoenvironmetal data associated with rangeomorph and erniettomorph taxa with symmetry and phylogenetic datasets to produce analyses of phyloecospace through time to evaluate the relative role of phylogeny and ecology in the evolution of symmetry in these groups. References: Liu, A.G., Kenchington, C.G. and Mitchell, E.G., 2015. Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota. Gondwana Research, 27(4), pp.1355-1380. Dunn, F.S. and Liu, A.G., 2019. Viewing the Ediacaran biota as a failed experiment is unhelpful. Nature ecology & evolution, 3(4), pp.512-514. Gibson, B.M., Furbish, D.J., Rahman, I.A., Schmeeckle, M.W., Laflamme, M. and Darroch, S.A., 2020. Ancient life and moving fluids. Biological Reviews.

Methods to be used

Computerised fluid dynamics, morphological phylogenetics, macroevolutionary analyses, field work

Specialised skills required

This project would suit a candidate with a background in Biology, Geology or a related discipline.

Please contact Frankie Dunn on frances.dunn@oum.ox.ac.uk if you are interested in this project