Unlocking the hidden diversity of organic-walled microfossils from the early Cambrian of North Greenland

Sammanfattning: The early Cambrian Buen Formation of North Greenland is celebrated for hosting one of the oldest Cambrian Burgess Shale-type deposits known to date – the Sirius Passet Lagerstätte. Further south in a shallower shelf facies belt, the Buen Formation yielded organic-walled microfossils (OWMs) that were originally described with a focus on acritarchs. Later sampling revealed a diversity of small carbonaceous fossils (SCFs) of metazoan origin. This PhD thesis investigates the diversity of OWMs from the Buen Formation using a novel combination of approaches. First, new samples are processed using a gentle acid maceration protocol designed for the recovery of large, delicate elements. Second, a population-based analysis of disparity is conducted to evaluate acritarch diversity, and illuminate the poorly known palaeobiology of these microfossils. New sampling revealed a remarkable diversity of metazoan fragments, including the oldest-known crustacean feeding apparatus, almost complete bradoriid valves preserved in three dimensions, new types of scalidophoran teeth and scalids, and a wide range of cuticular elements of uncertain affinity. Further, an abundance of large and/or asymmetrical acritarchs and filamentous microfossils was recovered, contributing to a rare but expanding record of benthic Proterozoic-like forms among Cambrian OWMs. The recovered diversity of acritarchs and filamentous microfossils totals 50 form taxa, of which 19 are described for the first time in the region. Quantitative and semi-quantitative analyses of acritarch disparity suggest a substantial proportion of these form taxa represent taphomorphs and/or arbitrary portions of abundance peaks. Placing form species in the context of their wider morphological variations allows the recorded diversity to be pared down to 30 morphotypes. On this basis, the presumed life history of Skiagia-plexus acritarchs is updated following quantitative analysis of openings, inner bodies, and clustering patterns in the recovered population. Three additional morphotypes are interpreted as bloom-forming and/or colonial species. Collectively, the results of this PhD project demonstrate that a fundamentally different picture of Cambrian diversity emerges when the full spectrum of OWM size ranges and disparity is considered. Applying these methods to the wider Cambrian record clearly shows potential to refine our understanding of macroevolution and palaeoecology as modern ecosystems were being established.