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

寒武纪早期动物生命的“爆发”是地球历史上最具变革性的事件之一，但潜在的模式和参与者很难解决。传统的贝利化石记录只代表了古代多样性的一小部分，而同时代的伯吉斯页岩型化石太罕见，没有代表性，无法追踪进化轨迹。然而，我们已经确定了一个新的、基本上被忽视的古生物数据来源，有望填补许多空白。“小型碳质化石”(SCF)是一种有机壁状化石，它们太小，在层理表面无法辨认，但又太大、太精致，无法用传统的微古生物学技术恢复。尽管SCF主要由脱节的骨痂和角质层碎片代表，但从根本上讲，SCF比它们的关节同行更常见和广泛分布。最重要的是，来自浅海环境的SCF记录揭示了一种前所未有的、令人惊讶的现代早期动物的多样性，我们最近的SCF工作非常成功，但仅限于寒武纪记录的‘后爆发’阶段。在这里，我们建议将对SCF的研究追溯到过去，着眼于追踪寒武纪爆发和之前的埃迪卡拉纪的演化模式。到目前为止，进行这项研究最有希望的地方是在波罗的海盆地记录充分的前寒武纪-寒武纪边界段。这些浅水层序保存得格外完好，化石丰富，易于获取--主要是通过爱沙尼亚、拉脱维亚、立陶宛和瑞典地质调查局的钻芯档案，以及塔林大学的独特研究收藏。我们在波罗的海盆地的主要关注点将是记录从埃迪卡拉纪晚期到寒武纪晚期的SCF的多样性和分布。我们特别感兴趣的是使用SCF记录来测试来自不同数据集的宏观进化模式，包括瑞典晚寒武世的‘小壳化石’和异常预先发现的节肢动物生物群。对有问题的SCF的显微结构分析有可能在埃迪卡拉纪确定明确的双边动物，具有重大的系统发育和宏观进化意义。结合相关古环境的地球化学分析和化石生物标记分子的寻找，这些新的古生物数据将为现代生物圈的起源提供新的基本线索。

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.