Behind the paper: ecosystem evolution of the first animals – PLOS Bilogue

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

Our new paper was the result of Becky Eden’s senior year undergraduate research project, which was first conceived by myself and Prof Andrea Manica† We are interested in the structure of ecosystems and what drives the complexity of ecosystems that we see today. The fossil record offers a different approach to understanding how complex ecosystem structures are related to ecosystem stability and resilience, as it allows us to examine 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, when many such innovations took place.

The macrofossils of the Ediacaran period form three major collections: the Avalon, the White Sea, and Nama. However, not all Ediacaran fossils fall neatly within the three major assemblages, such as the Lantian, Shibantan, or SW Brazil sites. Fossil assemblages are groups of fossil sites found in similar time periods and environments and containing similar fossils. For the most part, the three main assemblages span different time periods and environments. The oldest, the Avalon, has fossils found exclusively in deep water (~1 km deep) and consists of fossil sites mainly in Newfoundland, Canada and Charnwood Forest, here in the UK in Leicestershire. The White Sea assemblage has shallow water fossils and is mainly found in Australia and Russia while the Nama assemblage is mainly 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 photo. These fossils are from the Avalon assemblage, about 565 million years ago.
Australian fossils from the South Australia Museum, with a very large Dickinsonia on the right and a smaller Parvancorina next to it. These originate from the White Sea assemblage, about 555 million years ago.

This project was based on previously published data that included 86 different fossil sites around the world and 126 different taxa. As such, the project was completely computational. Becky was working on this project in addition to her lectures and interviews, so a lot of fantastic multitasking was involved. The work required running series of analyzes on her computer, then discussing her results and working out the next steps to understand the patterns we saw.

We didn’t expect the youngest Ediacaran assemblage, the Nama, to be the most complex – it’s the least diverse and most limited globally, so it was assumed to be a post-extinction recovery assemblage. Instead, we found that this is inconsistent with a maintenance of significant associations between species, an increase in depth specialization and a specialization of taxa to specific niches or environments. After extinction, we would expect generalists, not specialist animals, to thrive. Taken together, this work shows that the Ediacaran is largely the precursor to the Cambrian radiation, and that these Ediacaran organisms were the precursors of the Cambrian.

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

Metacommunity reconstructions by Becky Eden

This work is a wonderful example of how important academic research emerges from all career stages, including undergraduate work. We often think of science progressing through a lone genius sitting alone in their lab. However, this is largely not the case as science progresses within a network of researchers, from renowned professors and postdoctoral researchers to postgraduate and undergraduate students. All of these researchers contribute to science, but often, and especially for the younger members, these contributions are not fully appreciated, which is not only inaccurate, but can also be very disappointing for novice researchers. That is why it is so important that contributions to research are properly recognized.

About the author

Image by the author

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

#paper #ecosystem #evolution #animals #PLOS #Bilogue

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