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The evolution of sea floor ecology in the Cenozoic of Antarctica

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Sedgwick Club Conference 2020

Assessing changes in the ecology of fossil communities, and how this affected the evolution of marine life, gives insight into how modern communities will react to environmental change. Modern Antarctic sea floor invertebrate marine communities are described as archaic and retrograde, dominated by surface living suspension feeding organisms. Previous studies suggested this evolved in the Eocene, with cooling decreasing shell crushing predation. However, some recent evidence does not corroborate this hypothesis. Looking back to the start of the Cenozoic, the Cretaceous-Paleogene mass extinction did not cause a distinct change in Antarctic benthic community ecology, although the effects of the extinction in terms of species loss was comparable with other areas globally. Other global signals at this time, for example a shift in dominance between bivalves and gastropods, do occur in the Paleocene of Antarctica. During the Eocene, there was a radiation of many taxa. Stalked crinoids, the main evidence for the original hypothesis that Antarctic community structure arising at this time, are present. However, we have linked this to asynchronous timing of the Marine Mesozoic Revolution in the Southern Hemisphere. Evidence of the first glaciations in the west Antarctica comes from King George Island (South Shetland Islands). The Polonez Cove and Cape Melville Formations preserve marine sedimentary sequences from the Oligocene and Miocene. Dropstones, diamictites and striated rocks confirm deposition in a glacial environment. Both preserve abundant fossils, representing Antarctica’s first glacial sea floor communities. However, the youngest unit, does not preserve an invertebrate community with the modern Antarctic ecological structure. It is dominated by burrowing bivalves, with a significant proportion of shell crushing decapods. Overall the ecology of Antarctic taxa has links to climatic change, but the story is much more complex than previously thought, with links to predator and prey relationships and depositional environment.

Dr Rowan Whittle is a palaeobiologist at the British Antarctic Survey, Cambridge.

Her research aims to answer the question ‘How did Antarctic sea floor ecology evolve?’ Her studies have focussed on the effects of global events such as the Cretaceous- Paleogene (K-Pg) mass extinction on invertebrate communities, as well as tracing the fossil record of Antarctic invertebrates through time. Rowan has spent time collecting geological and biological samples in Antarctica to address these questions.

This talk is part of the Sedgwick Club talks series.

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