The emergence of animal ecosystems during the late Ediacaran (~571–539 million years ago) was a pivotal episode in the evolutionary history of life. Reconstructing the ecology of Ediacaran-aged organisms is crucial for establishing their role in the emergence of animals and the Ediacaran–Cambrian transition. However, many aspects of Ediacaran ecology remain uncertain, hampering efforts to decipher the origins of modern marine ecosystems. The goals of this project were to rigorously investigate the hydrodynamic performance of Ediacaran organisms and communities for the first time, using computer simulations, physical experiments, and fieldwork to establish how these life forms fed, moved, and reproduced.

Over the course of this project we have achieved the majority of our starting goals; the results of this work are reported in (to date) 11 published papers, with 3 more currently in review or accepted pending revision, and many more still in preparation. Our work has made significant steps towards understanding Ediacaran organisms and the ecology of the Ediacaran-Cambrian transition. A brief summary of these findings is given below, with references to specific papers where appropriate: 

1. We have shown using fluid dynamics modeling that some of the most bizarre and intractable Ediacaran taxa – despite still having little-understood relationships to extant animal groups – had ecologies and lifestyles that are widespread in the present day, and behaved and functioned in ways that we recognize. For example, we have shown that the triradial organism Tribrachidium was an efficient suspension feeder (Olaru et al., in revision) – a common strategy in the present day – and that the erniettomorph taxa Ernietta and Pteridinium almost certainly evolved gregarious ecologies to enhance feeding efficiency within clustered populations, much as modern oysters do (Gibson et al., 2020, 2021; Darroch et al., 2022). We have also shown that early Cambrian archaeocyathids almost certainly employed active ‘pumping’ of fluid, much like modern sponges, and thus would have been powerful ecosystem engineers during the earliest stages of the Cambrian and at the dawn of metazoan reef building (Gibson et al., 2023). At the broadest scale, the mounting evidence for suspension feeders in the late Ediacaran is forcing us to re-evaluate the character of these ecosystems, and has given rise to the idea that the rise of suspension feeding ~550-538 Ma –representing a vital link between pelagic and benthic realms – may have helped to ‘fuel’ the Cambrian explosion by enhancing the supply of nutrients to the seafloor (Cracknell et al., 2021). This hypothesis is something that our group is testing in ongoing work.

2. While the paleobiology of some Ediacaran organisms is coming into focus, our work is showing that others are still hard to understand, and suggesting that we may need to re-evaluate what little we thought we knew. Our work with the fence-like rangeomorph fossil Pectinifrons is an example; our CFD analyses showed that flow patterns around this organism were unlike anything seen either in fossils, or the extant carnivorous sponge Chondrocladia which possesses a similar body plan (Darroch et al., 2023a). We suggest that these flow patterns make more sense if the rangeomorph body plan evolved as an adaptation for scavenging oxygen, rather than feeding as previously thought. This inference is supported by our ongoing work (Gutarra-Diaz et al., in revision) reconstructing entire rangeomorph communities, and showing that the unique arrangement of these marine ‘forests’ on the continental shelf would have enhanced vertical mixing of the water column, potentially creating local-scale oxygen oases and fostering the evolution of more energy-intensive behaviors. 

3. Lastly, by reconstructing the paleoecology and -biology of organisms over the Ediacaran-Cambrian transition using fluid dynamics, we are discovering patterns of apparent selectivity over putative extinction pulses, allowing us to develop more targeted hypotheses surrounding what these events represent…as well as what drove them. After reviewing patterns of diversity through time, we showed that a ‘first pulse’ of Ediacaran extinction coincided with the loss of low-tier suspension feeders, leaving more mobile taxa, as well as higher-tier suspension feeders to thrive in the very latest Ediacaran (Darroch et al., 2023b). We suggest in this paper that one possible driver of this pattern could hinge on the evolution of bioturbation – the process of sediment mixing by organisms – and which our fieldwork in Namibia indicates was diversifying at this point. In the present day, bioturbation can lead to the re-suspension of sediment, which can clog filter-feeding organs in a process referred to as ‘trophic group amensalism’ by modern ecologists. This finding offers tantalizing hints that late Ediacaran extinction may have been driven, at least in part, by the evolution of new behaviors and feeding modes, offering powerful analogies for present-day patterns of diversity loss.

Lastly, we have developed new computational tools in fluid dynamics modeling that have wide applicability in studying both modern, and fossil organisms through geological time.

Last Modified: 03/19/2024
Modified by: Simon A Darroch