A hidden record of early animal evolution? Exploring the Cambrian diversity of acritarchs and small carbonaceous fossils.

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Overview: Microfossils offer a rich record of early animal evolution and the attendant reconfiguring of ecosystems. This project will focus on exceptionally well-preserved acritarchs and small carbonaceous fossils (SCFs) to reach a new understanding of how animals dramatically changed the biosphere around half a billion years ago, in the Cambrian evolutionary 'explosion'. The project aims to discriminate between animal- and non-animal microfossils, and constrain their biological affinities, modes of life, and distributions in space and time. The results will bring key insights into changes in diversity and ecology through a pivotal interval in Earth history.Acritarchs are organic-walled microfossils of unknown affinity, extracted using standard palynological laboratory techniques. In contrast, more gentle procedures yield larger, more delicate SCFs that represent a range of organisms, including a diversity of animals. Despite this categorization, the two datasets overlap. Recently, we have begun to explore a combined approach, which promises to shed light on the affinities and significance of both acritarchs and SCFs, enhancing their application to key questions in palaeobiology, stratigraphy, and ancient ecosystems. The project will focus initially on exceptionally well-preserved acritarchs and SCFs from the Forteau Formation of Newfoundland, Canada (Cambrian Stage 4, c. 510 million years ago). Hundreds of SCFs and thousands of acritarchs have already been prepared onto glass slides for analysis. In light of the SCFs, some palynomorphs are clearly derived from animals including arthropods, priapulid worms, and the slug-like Wiwaxia. Others remain enigmatic, such as the conical acritarchs known as Ceratophyton and Corollasphaeridium, which could represent animals or perhaps protists. At the same time, SCF-processing yields clumps, articulated arrays, and even faecal-pellets full of acritarchs, constraining their biological interpretation. Therefore, the Forteau material offers an unrivalled opportunity to resolve the affinities and ecologies of otherwise mysterious Cambrian microfossils. Any insights can then be applied more widely to help constrain the largest-scale patterns and processes of the Cambrian 'explosion'. For example, do animal-derived microfossils extend back into the Ediacaran? Can acritarchs tell us about the structure of the plankton? And how did ecosystems respond to major events in evolution? Figure 1: Selection of lower Cambrian microfossils, each measuring around 20 to 40 microns in size; they include two spiny acritarchs alongside conical and spine-tipped forms that could represent unicellular protists or animal body parts.