The evolution of organism sediment interactions in the early benthos

埃迪卡拉生物群的演化及其向中生代后生动物生物群的过渡仍然是对现代古生物学的一个重大挑战。 经典埃迪卡拉生物群的一个显著特征是，除极少数例外，它们主要是不动的表生底栖生物。这种不动性很可能对生物本身构成了重大挑战，因为硫化氢往往会在沉积物-水界面的任何物体下积聚，切断含氧海水的供应。我们最近提出，具有高表面积的倾斜埃迪卡拉类群不仅适应于科普硫化氢，而且可能实际上使用硫化氢与生态共生或内共生的硫营养细菌共生。这一推论有许多含义，我的学生、同事和我打算在未来几年进行探索。 拟议的研究方案旨在通过以下几条调查路线的探索，解决对底栖生物早期演变的一些相互关联的方面及其与埃迪卡拉-寒武纪过渡期海底生态系统演变的关系缺乏了解的问题： 1)的rangeomorphic占主导地位的软体组合的埃迪卡拉在阿瓦隆需要重新评估的启示，埃迪卡拉生物群可能有化学共生体，以确定哪些元素的埃迪卡拉生物群可能是沉积物躺椅（微生物沉积物系统的一部分），以及生物直立在水柱中，许多作者已经假设。这一认识对于切实评估埃迪卡拉生物群的古生物学、古生态学和演化至关重要，因为埃迪卡拉生物群的大多数类群通常直立在水柱中，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纪晚期小型底栖动物洞穴（及其对生态系统的潜在影响），有必要广泛寻找小型底栖动物生物扰动。在这方面，新发现的有机有孔虫衬里和凝集试验从565马在床与小型底栖生物扰动保存在matgrounds下面必须探索，以更好地了解哪些动物是第一个穴居人，因此如何穴居进化。 3)纽芬兰的Burin半岛的后埃迪卡拉纪（即寒武纪）富含遗迹化石的动物群代表了在沉积物-水界面下打洞的最早证据，但很少通过连续研磨、详细的岩相学和地球化学分析对单个洞穴进行研究。这种自下而上的方法是需要地面真理断言，主要是基于大量的沉积物代理全球海洋化学。 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.