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探索。拟议的研究计划旨在解决缺乏了解的一些相互关联的方面的早期演变的底栖生物及其关系的海底生态系统的演变，通过埃迪卡拉-寒武纪过渡通过几条线的调查探索：1）根据埃迪卡拉生物群可能有化学共生体的启示，需要重新评估阿瓦隆尼亚埃迪卡拉生物群中以岭型为主的软体生物组合，以确定埃迪卡拉生物群的哪些成分可能是沉积物倾斜者（微生物-沉积物系统的一部分），以及如许多作者所假设的那样，哪些生物直立在水柱中。这一认识对于现实地评估埃迪卡拉纪生物群的古生物学、古生态学和演化至关重要，埃迪卡拉纪生物群通常直立在水柱中，而不是沿着沉积物-水界面生长。2）随着我们最近对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）的认识，需要广泛寻找小型底栖动物生物扰动。在这方面，必须探索565 Ma以来在床层中发现的有机有孔虫衬里和凝集试验，这些床层中保存有小型底栖生物扰动，以更好地了解哪些动物是第一批穴居动物，以及穴居是如何进化的。3）后埃迪卡拉纪（即寒武纪）痕迹-纽芬兰的伯林半岛化石丰富的动物群代表了在沉积物-水界面下打洞的最早证据，但在单个洞穴尺度上，通过连续研磨和详细的岩相学和地球化学分析进行的研究很少。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.