The early evolution of animal life and the generation of form

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• Frances Dunn, Oxford University Museum of Natural History & University of Oxford
• Tuesday 10 June 2025, 12:00-13:00
• Department of Earth Sciences, Tilley Lecture Theatre.

If you have a question about this talk, please contact Dr Rachael Rhodes.

The radiation of animals across the Ediacaran-Cambrian transition is one of the most transformational events in Earth history, representing a step change in the evolution of the biosphere. While fossils from the Cambrian are readily recognised as belonging to extant groups, those from the late Ediacaran Period document organisms with distinctive forms and no counterparts among living species. This has resulted in a number of different phylogenetic interpretations, ranging from animals to fungi to an extinct Kingdom but with little historical consensus. In this talk, I will focus on the rangeomorphs – frond-like taxa with ‘fractal’ branching – which are among the oldest Ediacaran macrofossils. My work uses morphogenetic pattern to produce a phylogenetic bracket for the rangeomorphs and this study of Ediacaran developmental biology has identified them as animals and stem-group eumetazoans to the exclusion of alternatives. Rangeomorphs thus occupy a critical position in the tree of animal life, post-dating the origin of true tissues and body axes, but likely pre-dating the origins of a gut and other defining eumetazoan characters. This conclusion enables us to integrate rangeomorphs into debates concerning the mode of early animal evolution, for example, in the influence of the evolving regulatory genome on the evolution of animal complexity. Some authors have suggested that a step-change in the regulation of early-acting genes implicated in development may explain the burst of morphological variety which underpins the Cambrian Explosion. However, our data suggest that rangeomorph growth was conserved and predictable with a morphogenetic strategy that was highly regulated, demonstrating that the most ancient eumetazoan fossils known already manifest evidence of complex developmental regulation. Instead, we suggest that the evolution of the rangeomorphs (and other Ediacaran macrofossils) may have catalysed the explosion of morphological variety observed during the Cambrian Explosion by promoting the diversification of novel phenotypes and behaviours through the introduction of space- and time-limited resources, resulting in a rougher fitness landscape than earlier in Earth history. Previous studies have implicated a roughening of the fitness landscape as a potential driver for the Cambrian Explosion but this hypothesis remains untested. Using eco-evolutionary simulations we propose that morphological disparity is an emergent property of a roughening fitness landscape providing a possible mechanism for saltational jumps in the evolution of morphological disparity through time, including during the Cambrian Explosion.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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• Department of Earth Sciences Seminars (downtown)
• Department of Earth Sciences seminars
• Department of Earth Sciences, Tilley Lecture Theatre
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