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Behind the paper: ecosystem evolution of the first animals

In this ‘behind the paper’ post, Emily Mitchell discusses the value of getting undergraduate students involved in research projects.   

Our new paper was the result of the final year undergraduate research project of Becky Eden, that was first thought of by myself and Prof Andrea Manica. We are interested in ecosystem structure, and what drives the complexity of ecosystems we see today. The fossil record provides a different approach for understanding how complex ecosystem structures relate to ecosystem stability and resilience because, through it, we can investigate ecosystem structure prior to the evolution of major innovations, such as mobility, predation or vertebrates. The subject of Becky’s project was the Ediacaran time period, which is when many such innovations occurred. 

The macrofossils of the Ediacaran period form three major assemblages: the Avalon, White Sea and Nama. However, not all Ediacaran fossil sites fall neatly within 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, environments and contain similar fossils. For the most part, the three major assemblages cover different time periods and environments. The oldest, the Avalon, has fossils found exclusively in a deep-water setting (~1 km deep) and consists of fossil localities mainly in Newfoundland, Canada and Charnwood Forest, here in the UK in Leicestershire. The White Sea assemblage has shallow water fossils and is found mainly in Australia and Russia, while the Nama assemblage is mostly found in Namibia. 

The Ediacaran fossil surface of Mistaken Point, Newfoundland, Canada, with Dr Charlotte Kenchington collecting photographic data in the left background of the photograph. These fossils are from the Avalon assemblage, around 565 million years ago.
Image credit

Photo by Emily Mitchell

Australian fossils from the South Australia Museum, showing a very large Dickinsonia to the right and a smaller Parvancorina near it. These are from the White Sea assemblage, around 555 million years ago.
Image credit

Photo by Emily Mitchell

This project was based upon previously published data that included 86 different fossil localities across the world and 126 different taxa. As such, the project was completely computational. Becky worked on this project alongside doing her lecture courses and applying for jobs, so lots of fantastic multitasking was needed. The work required running suites of analyses on her computer, then discussing her results all together and working out the next steps to understand the patterns we were seeing.

We were not expecting the youngest Ediacaran assemblage, the Nama, to be the most complex — it is the least diverse and most globally restricted assemblage, so was thought to be a post-extinction recovery assemblage. Instead we found that this is inconsistent with a maintenance in significant associations between species, an increase of depth specialization and a specialization of taxa to specific niches or environments. Post-extinction, we would expect generalists, not specialist animals, to prosper. Taken together this work demonstrates that the Ediacaran is very much the run up to the Cambrian radiation, and that these Ediacaran organisms were the precursors to the Cambrian ones.

Top is Avalon assemblage, showing the community as they mature from left to right, middle the White Sea with the Russian (left) and Australian (right) and bottom is Nama showing the depth gradient.
Image credit

Metacommunity reconstructions by Becky Eden

This work is a wonderful example of how important academic research comes from all career stages, including undergraduate work. Often we think of science progressing through a lone genius sitting by themselves in their lab.  However this is very much not the case, with science progressing within a network of researchers, from well established professors, and post-doctoral researchers to post-graduate and undergraduate students. All of these researchers contribute to science, but often, and especially for the more junior members, these contributions are not fully appreciated, which is not only inaccurate but also can be very disillusioning for early career researchers. As such, it is so important that the contributions for research are appropriately acknowledged.

About the author

Image of the author

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

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