Caught in the Cambrian Explosion: The mystery of the early evolution of the Pterobranchs (Hemichordata, incl. Graptolithina) and their evolutionary innovations

寒武纪大爆发是大多数现代门类起源的时间间隔。然而，化石记录只在一定程度上支持了这一观点。第一个确定的翼缘半角类(如笔石及其近缘)在中寒武世(系列3，阶段5)很常见，但存在更早分类群的证据越来越多。这些分类群接近翼支目的进化起源，并阐明了与剩余的半角类动物(如Enteropneusta)的系统发育关系。新的古生物化学提取有机保存的生物遗骸的方法有助于揭开早期半角类特别是翼手类进化的早期历史。浅水、深色页岩和石灰岩序列产生了一个具有尚未开发的巨大价值的化石档案。这些地层开始产生意想不到的丰富的有机保存的遗体化石(也被称为SCF；小型碳质化石)，除了更正常的化石贝壳矿物保存，典型的寒武纪外壳动物群(例如，小型外壳动物群；SSFS)。纽芬兰西部下寒武统Forteau组沉积序列热叠置程度低，构造变形适中，适合酸性溶解，特别是温和氢氟酸技术提取化石。此外，还将对中国的凯里组进行研究，这是一个著名的拉格斯塔特组，在另一个不同的古大陆上保存了壮观的化石。世界上许多地区的下寒武统缺乏足够的和足够广泛的宏大化石来进行详细的生物地层学。由于国际相关性的不确定性，常规化石带或化石组合最近受到了质疑。有机保存化石的提取为下寒武统生物地层学研究提供了新的工具。它还通过关注化石组合中通常不认识的生物群，帮助更好地了解寒武纪爆发的节奏和模式。

The Cambrian explosion is the time interval when most of modern phyla originated. However, the fossil record only in part supported this idea. First definitive pterobranch hemichordates (e.g. graptolites and their relatives) are common in the Middle Cambrian (Series 3, Stage 5), but the evidence for the presence of even earlier taxa is mounting. These taxa are close to the evolutionary origin of the pterobranchs and shed light on the phylogenetic relationships to the remaining hemichordates (e.g. Enteropneusta). New palaeontological methods of chemical extraction of organically preserved organismic remains help to unravel the early history of the evolution of early hemichordates and especially pterobranchs. Shallow water dark shale and limestone successions yield a fossil archive of immense value not yet explored. These strata start to yield unexpected richness of organically preserved body fossils (also known as SCFs; Small carbonaceous fossils) aside the more normal mineral preservation of fossil shells, the typical Cambrian shelly faunas (e.g. Small Shelly Faunas; SSFs). The Lower Cambrian Forteau Formation of western Newfoundland provides a sedimentary succession with low thermal overprint and moderate tectonic distortion that is ideal for the fossil extraction with the means of acidic dissolution, especially with gentle hydrofluoric acid techniques. Additionally, research will be done in the Chinese Kaili Formation, a well-known lagerstätte with spectacular fossil preservation on a different palaeo-continent. The Lower Cambrian in many regions of the world lacks sufficient and widely enough distributed macrofossils for a detailed biostratigraphy. Conventional fossil zones or assemblages have been questioned recently due to uncertainties of international correlation. The extraction of organically preserved fossils provides a new tool support the biostratigraphy of the Lower Cambrian. It also helps to better understand tempo and mode of the Cambrian explosion by focusing on groups of organisms not usually recognized in the fossil assemblages.