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 has contributed significantly to our knowledge of early metazoans, yet the fossil remains of primary producers from this deposit have received less attention. Here we examine the palynological component of the Buen Formation, with a focus on acritarchs and filamentous microfossils. Our analysis revealed the 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. <i>Comasphaeridium longispinosum</i> Vidal 1993 is renamed <i>Comasphaeridium</i>? <i>brillesensis</i> nom. nov., and <i>Comasphaeridium densispinosum</i> Vidal 1993 is reassigned to a new genus, <i>Pearisphaeridium</i>, becoming <i>Pearisphaeridium densispinosum</i> comb. nov. The diagnoses of <i>Pearisphaeridium densispinosum</i> (Vidal 1993) comb. nov. and <i>Skiagia pura</i> Moczydłowska 1988 are emended. Further, careful analysis of disparity in the recovered assemblage has revealed the presence of numerous transitional morphologies among the recorded acritarch form taxa. Though some of these transitional forms likely represent biologically meaningful entities (e.g., life cycle stages, ecophenotypes), others appear to have been artificially generated by taphonomic processes. Accounting for taphonomic factors and other sources of morphological variation has curtailed diversity down to 30 acritarch morphotypes, ten of which represent distinct abundance peaks broadly corresponding to acritarch genera. This analysis illustrates how population-based studies of early Cambrian acritarchs can help to discern the different factors that impinge on acritarch morphology, detect instances of taxonomic inflation, and refine our measures of diversity at the base of early Palaeozoic food webs.

寒武纪早期北格陵兰地区的布恩组（Buen Formation）产出了极为丰富的特异埋藏化石群，极大推动了学界对早期后生动物的认知，但该化石库中初级生产者的化石遗存却未得到足够关注。本文对布恩组的孢粉组合展开研究，重点聚焦疑源类（acritarchs）与丝状微化石。分析结果显示，共识别出49个形态分类群，其中15个为布恩组首次报道。这些类群包括推测为底栖起源的大型化石，以及囊状疑源类。原<italic>Comasphaeridium longispinosum</italic> Vidal 1993被修订为<italic>Comasphaeridium</italic>? <italic>brillesensis</italic> nom. nov.（新名称）；原<italic>Comasphaeridium densispinosum</italic> Vidal 1993被归入新属<italic>Pearisphaeridium</italic>，形成新组合<italic>Pearisphaeridium densispinosum</italic> comb. nov.（新组合）。本次研究还修订了<italic>Pearisphaeridium densispinosum</italic> (Vidal 1993) comb. nov.与<italic>Skiagia pura</italic> Moczydłowska 1988的鉴别特征。进一步对所获化石组合的形态分异度开展细致分析后发现，已记录的疑源类形态分类群中存在大量过渡形态。其中部分过渡形态可能代表具有生物学意义的实体（如生命周期阶段、生态表型），其余则可能由埋藏学作用人为产生。在考量埋藏学因素与其他形态变异来源后，疑源类的多样性被修正为30个形态型，其中10个对应丰度峰值显著的疑源类属级类群。本研究表明，针对寒武纪早期疑源类开展基于种群的研究，有助于厘清影响疑源类形态的各类因素、识别分类学膨胀案例，并优化学界对早古生代食物网基部类群多样性的评估方法。