The evolution of organism sediment interactions in the early benthos

埃迪卡拉生物群的演化及其向显生界遗迹的后生动物生物群的过渡是对现代古生物学的重大挑战。经典的埃迪卡拉生物群的一个决定性特征是，除了极少数例外，它们主要是非运动性的附生底栖生物。这种不动很可能对生物体本身构成重大挑战，因为硫化氢往往会在沉积物-水界面的任何物体下积聚，从而切断含氧海水的供应。我们最近提出，具有高表面积的斜卧埃迪卡拉分类群不仅适应于应对硫化氢，而且实际上可能利用这种硫化氢与生态共生或内共生硫代营养细菌共生。这一推论有许多含义，我的学生、同事和我打算在未来几年探索这些含义。 拟议的研究方案旨在通过探索几条调查路线，解决对底栖生物早期演化的若干相互关联的方面及其与埃迪卡拉纪-寒武纪过渡期间海底生态系统演变的关系缺乏了解的问题： 1)根据埃迪卡拉纪生物群可能具有化学共生体的揭示，需要重新评估阿瓦洛尼亚埃迪卡拉纪以范围形态为主的软体组合，以确定埃迪卡拉纪生物群中哪些元素可能是沉积物倾斜体(微生物-沉积物系统的一部分)，以及哪些生物如许多作者假设的那样竖立在水柱中。这一认识对于现实地评估埃迪卡拉纪生物群的古生物学、古生态学和演化具有关键意义，该生物群的大多数埃迪卡拉族分类群通常竖立在水柱中，而不是沿着沉积物-水界面生长。 2)随着我们最近认识到埃迪卡拉晚期的小型动物洞穴(及其对生态系统的潜在影响)，有必要对小型动物的生物扰动进行广泛的研究。在这方面，必须探索新的有机有孔虫衬里的发现和565 Ma以来在草场下保存着小型动物生物扰动的床上的凝集试验，以更好地了解哪些动物是最早的洞穴动物，因此洞穴是如何进化的。 3)纽芬兰伯林半岛后埃迪卡拉纪(即寒武纪)遗迹化石丰富的动物群是沉积物-水界面下埋藏的最早证据，但通过系列研磨和详细的岩石学和地球化学分析，在单个洞穴规模上研究较少。这种自下而上的方法是需要的，以证明在很大程度上基于全球海洋化学的块状沉积物代用品的真理断言。这些方法将使我们能够更好地了解最早的动物洞穴及其对早期海底的影响。

The evolution of the Ediacara biota and its transition into the metazoan biotas of the Phanerozoic remains as a significant challenge to modern paleontology. One of the defining characters of the classical Ediacaran biota is that, with few rare exceptions, they were dominantly non-motile epi-benthos. This immobility is likely to have posed a significant challenge to the organisms themselves since hydrogen sulfide tends to build up under any object at the sediment-water interface that cuts off the supply of oxygenated seawater. We have recently proposed that reclining Ediacaran taxa with high surface areas were adapted to not only cope with hydrogen sulphide, but may have actually used that hydrogen sulphide to fuel a symbiosis with either ecosymbiotic or endosymbiotic thiotrophic bacteria. That inference has a number of implications that my students, colleagues and I intend to explore in the coming years. The proposed program of research aims to address the lack of understanding of a number of inter-related aspects of the early evolution of the benthos and their relationship to the evolution of seafloor ecosystems through the Ediacaran-Cambrian transition via the exploration of several lines of investigation: 1) The rangeomorph-dominated soft-bodied assemblages of the Ediacaran in Avalonia need to be reassessed in the light of the revelation that the Ediacaran biota might have had chemosymbionts, in order to determine which elements of the Ediacaran biota might be sediment recliners (part of the microbe-sediment system), and which organisms were erect in the water column as many authors have assumed. This understanding is key importance for realistically assessing the palaeobiology, palaeoecology and evolution of the Ediacaran biota, which usually has most Ediacaran taxa erect in the water column instead of growing along the sediment-water interface. 2) With our recent recognition of late Ediacaran meiofaunal burrows (and their potential impact on ecosystems) there is a need for an extensive search for meiofaunal bioturbation. In this respect, new discoveries of organic foraminiferal linings and agglutinated tests from 565Ma in beds with meiofaunal bioturbation preserved below matgrounds must be explored to better understand which animals were the first burrowers, and therefore how burrowing evolved. 3) The post Ediacaran (i.e. Cambrian) trace-fossil rich faunas of the Burin Peninsula of Newfoundland represent the earliest evidence for burrowing below the sediment water interface, but have been little studied at the scale of individual burrow through serial grinding, and detailed petrographic and geochemical analysis. This bottom-up approach is needed to ground-truth assertions that have largely been based on bulk-sediment proxies for global oceanic chemistry. These approaches will allow us to better understand the earliest animal burrows and their impact on the early seafloor.