Organic-walled microfossils from the lower Cambrian of North Greenland: a reappraisal of diversity

The early Cambrian Buen Formation (North Greenland) hosts an exceptionally rich fossil biota that hascontributed significantly to our knowledge of early metazoans, yet the fossil remains of primary pro-ducers from this deposit have received less attention. Here we examine the palynological componentof the Buen Formation, with a focus on acritarchs and filamentous microfossils. Our analysis revealedthe presence of 49 form taxa, 15 of which are described for the first time in the Buen Formation.These include large elements of presumably benthic origin, together with cyst-like acritarchs.Comasphaeridium longispinosum Vidal 1993 is renamed Comasphaeridium? brillesensis nom. nov., and Comasphaeridium densispinosum Vidal 1993 is reassigned to a new genus, Pearisphaeridium, becomingPearisphaeridium densispinosum comb. nov. The diagnoses of Pearisphaeridium densispinosum (Vidal1993) comb. nov. and Skiagia pura Moczydłowska 1988 are emended. Further, careful analysis of dis-parity in the recovered assemblage has revealed the presence of numerous transitional morphologiesamong the recorded acritarch form taxa. Though some of these transitional forms likely represent bio-logically meaningful entities (e.g. life cycle stages, ecophenotypes), others appear to have been artifi-cially generated by taphonomic processes. Accounting for taphonomic factors and other sources ofmorphological variation has curtailed diversity down to 30 acritarch morphotypes, ten of which repre-sent distinct abundance peaks broadly corresponding to acritarch genera. This analysis illustrates howpopulation-based studies of early Cambrian acritarchs can help to discern the different factors thatimpinge on acritarch morphology, detect instances of taxonomic inflation, and refine our measures ofdiversity at the base of early Palaeozoic food webs.