Reconstructing the Cambrian explosion using Small Carbonaceous Fossils: Ediacaran to Cambrian SCFs in the Baltic Basin

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The Cambrian 'explosion' of early animal life was one of the most transformative events in Earth history, but the underlying patterns and players are difficult to resolve. The conventional shelly fossil record represents only a fraction of ancient diversity, while contemporaneous 'Burgess Shale-type' fossils are too rare and unrepresentative to track evolutionary trajectories. We have, however, identified a new and largely overlooked source of palaeontological data that promises to fill in many of the gaps. 'Small Carbonaceous Fossils' (SCFs) are organic-walled fossils that are too small to be identified on bedding surfaces, but too large and delicate to be recovered by conventional micropalaeontological techniques. Although mostly represented by disarticulated sclerites and cuticle fragments, SCFs are fundamentally more common and widely distributed than their articulated counterparts. Most significantly, the SCF record from shallow marine environments is revealing an unprecedented, and surprisingly modern, diversity of early animals, Our recent SCF work has been extraordinarily successful, but limited to 'post-explosion' phases of the Cambrian record. Here we propose to extend the study of SCFs back in time, with an eye to tracking evolutionary patterns through the Cambrian explosion and into the preceding Ediacaran Period. By far the most promising place to carry out such a study is in well-documented Precambrian-Cambrian boundary sections of the Baltic Basin. These shallow water successions are exceptionally well preserved, richly fossiliferous and easy to access - primarily through drillcore archives at the geological surveys of Estonia, Latvia, Lithuania and Sweden, along with a unique research collection at the Tallinn University. Our primary focus in the Baltic Basin will be in documenting the diversity and distribution of SCFs from the late Ediacaran through to the late Cambrian. We are particularly interested in using the SCF record to test macroevolutionary patterns derived from alternative datasets, including 'small shelly fossils' and execeptionally preseved arthropod biotas in the late Cambrian of Sweden. Microstructural analysis of problematic SCFs have the potential to identify unambiguous bilaterian animals in the Ediacaran, with major phylogenetic and macroevolutionary implications. Combined with geochemical analysis of associated palaeoenvironments, and a search for fossil biomarker molecules, these novel paleontological data will shed fundamental new light on the origin of the modern biosphere.