Behind the paper: evolution of the ecosystem of the first animals

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In this article “behind the paper”, Emily Mitchell discusses the value of involving undergraduate students in research projects.

Our new article is the result of Becky Eden’s final year undergraduate research project, which I first thought of with Professor Andrea Manica. We are interested in the structure of ecosystems and what drives the complexity of the ecosystems we see today. The fossil record offers a different approach to understanding how complex ecosystem structures relate to ecosystem stability and resilience because through it we can study ecosystem structure before major innovations evolved, such as mobility, predation or vertebrates. The subject of Becky’s project was the Ediacaran period, when many such innovations occurred.

Macrofossils from the Ediacaran period form three major assemblages: the Avalon, the White Sea and the Nama. However, not all Ediacaran fossil sites fall neatly into the three main assemblages, such as the Lantian, Shibantan, or SW Brazil sites. Fossil assemblages are groups of fossil sites that are found in similar time periods and environments and contain similar fossils. For the most part, the three major assemblages span different eras and environments. The oldest, the Avalon, has fossils found exclusively in deep water (~1km deep) and consists of fossil localities primarily in Newfoundland, Canada and Charnwood Forest here in the UK in Leicestershire. The White Sea assemblage has shallow water fossils and is mostly found in Australia and Russia, while the Nama assemblage is mostly found in Namibia.

The Ediacaran fossil surface from Mistaken Point, Newfoundland, Canada, with Dr. Charlotte Kenchington collecting photographic data in the left background of the photograph. These fossils come from the Avalon assemblage, around 565 million years ago.
Australian Fossils from the South Australia Museum, showing a very large Dickinsonia on the right and a smaller Parvancorina nearby. These come from the White Sea assemblage, about 555 million years ago.

This project was based on previously published data that included 86 different fossil localities around the world and 126 different taxa. As such, the project was entirely computer-based. Becky worked on this project alongside her lectures and applying for jobs, so a lot of fantastic multitasking was required. The job involved running suites of analyzes on his computer, then discussing his results together and working out next steps to understand the patterns we were seeing.

We did not expect the youngest Ediacaran assemblage, the Nama, to be the most complex – it is the least diverse and restricted assemblage globally, so it was thought to be of a post-extinction recovery assembly. Instead, we found that it is inconsistent with maintaining meaningful associations between species, increasing specialization at depth, and specializing taxa in specific niches or environments. After extinction, we would expect generalists, not specialists, to thrive. Taken together, these works demonstrate that the Ediacaran is largely the current that preceded the Cambrian radiation and that these Ediacaran organisms were the precursors of the Cambrian organisms.

The top is the Avalon assembly, showing the community as it matures from left to right, the middle is the White Sea with Russian (left) and Australian (right), and the bottom is Nama showing the depth gradient.
image credit

Metacommunity reconstructions by Becky Eden

This work is a wonderful example of the importance of academic research at all career stages, including undergraduate studies. Often we think of science advancing through a solitary genius sitting alone in his laboratory. However, this is not the case at all, with science progressing through a network of researchers, ranging from well-established professors and postdoctoral researchers to postgraduate and undergraduate students. All of these researchers contribute to science, but often, and especially for younger members, these contributions are not fully appreciated, which is not only inaccurate but can also be very disappointing for early career researchers. As such, it is so important that contributions to research are duly recognized.

About the Author

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Dr. Emily G. Mitchell is a NERC Research Fellow in the Department of Zoology at the University of Cambridge. 0000-0001-6517-2231 @EGMitchell @DeepTimeEcology

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