The dawn of the Phanerozoic: non-bilaterian evolution and the nature of the Cambrian Explosion

显生宙的黎明：非两侧对称演化和寒武纪大爆发的本质

• 批准号: NE/W00786X/1
• 负责人: Frances Dunn
• 金额: $ 77.17万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW00786X%2F1
• 关键词: dawn; Phanerozoic; non; bilaterian; evolution

The rise of the animals was a profound transition in the History of Life; for the first-time organisms were able to engineer the environment around them, altering geochemical cycles, building complex ecosystems and diversifying into myriad forms. However, the rise of the animals is also one of the most controversial episodes in Earth History. Recognisable animals appear in the fossil record in great number during the Cambrian Period - the so-called 'Cambrian Explosion', but Darwin's theory of evolution by natural selection demands a longer evolutionary history of animals, stretching deep into the Precambrian (between 4,000-539 million years ago). Indeed, data from DNA also suggests a deep Precambrian root for the animals and this mismatch gets larger the closer we go to the root of the animal tree, for example, the mismatch between genetic estimates for the origin of sponges and the accepted fossil record of that group is on the order of hundreds of millions of years. I intend to better constrain the origin and diversification of animals by studying these particularly ancient lineages, like sponges. Most studies looking at this question tend to focus on bilaterian animals - animals with left-right symmetry - but the older non-bilaterian lineages which, by virtue of their greater age are likely to have a more protracted fossil record have been understudied. This proposal seeks to redress the balance by achieving three distinct research objectives: 1) The Ediacaran (latest Precambrian) macrobiota, which appear in the fossil record around 570 million years ago are a group of organisms with long-extinct bodyplans but that increasing evidence is showing that at least some of which represent the remains of ancient non-bilaterian animals. Because of their strange anatomies they are not often included in studies on the early evolutionary history of the animals and so remain something of an elephant-in-the-room. I intend to study the youngest of the Ediacaran macrobiota - the erniettomorphs - which are a group of organisms made up of serially-repeated tubes - and are amongst the most enigmatic, with no consensus about what they were or, indeed, were not. I will study their affinities by analysing how these organisms grew and developed, using a methodology I have previously designed. I will also establish the evolutionary trajectory of the erniettomorphs as relating to other animals (if appropriate) through a combination of field work and studying museum collections in order to work out when they stopped innovating (varying their bodyplans) and when they went extinct.2) Sponges are often considered to be the most ancient animal lineage, but the oldest widely accepted sponge body fossils are only Cambrian in age. There are, however, a number of putative Ediacaran sponges which may go some way to extend the fossil record more in line with molecular expectations. I will re-examine the morphology of these fossils using large photo datasets and new and unpublished field specimens to assess whether they likely represent ancient sponges. I will also use computational fluid dynamics - a technique which models fluid flow around organisms - to assess whether the anatomy of these fossils allowed them to function as living sponges do. If any of these fossils are likely to be ancient sponges, I will include them in a morphological phylogenetic analysis to understand the sponge tree of life, alongside other, younger sponge fossils. I will then integrate this anatomical and fossil-age data with DNA data to establish the most rigorous estimate of the age of the sponges. 3) I will integrate the above data with previously collected data on other members of the Ediacaran macrobiota and cnidarians (the group containing anemones, corals and jellyfish) to ask whether the rate of anatomical change in the non-bilaterian animals was indeed faster in the late Precambrian (Ediacaran) or conforms to the expectations of the Cambrian Explosion hypothesis.

动物的出现是生命史上一个意义深远的转变；生物第一次能够改造它们周围的环境，改变地球化学循环，建立复杂的生态系统，并多样化成无数种形式。然而，动物的崛起也是地球历史上最具争议的事件之一。可识别的动物在化石记录中大量出现在寒武纪时期——即所谓的“寒武纪大爆发”，但达尔文的自然选择进化理论要求动物的进化史更长的时间，深入到前寒武纪（4000 - 5.39亿年前）。事实上，来自DNA的数据也表明，这些动物有一个深前寒武纪的根源，而且这种不匹配越大，我们越接近动物树的根源，例如，对海绵起源的遗传估计和对该群体的接受的化石记录之间的不匹配大约是数亿年。我打算通过研究这些特别古老的谱系，比如海绵，来更好地约束动物的起源和多样化。大多数关于这个问题的研究都倾向于关注左右对称的两侧动物，但是更古老的非两侧动物谱系，由于它们的年龄更大，可能有更长的化石记录，一直没有得到充分的研究。这一建议试图通过实现三个不同的研究目标来纠正这种平衡：1)埃迪卡拉纪（最新的前寒武纪）大型生物群，在大约5.7亿年前的化石记录中出现，是一群身体结构早已灭绝的生物，但越来越多的证据表明，其中至少有一些代表了古代非双边动物的遗骸。由于它们奇特的解剖结构，它们不常被纳入动物早期进化史的研究中，因此在某种程度上仍然是房间里的大象。我打算研究埃迪卡拉动物群中最年轻的一种巨生动物——异形虫——这是一组由连续重复的管子组成的生物——也是最神秘的生物之一，对于它们是什么，或者实际上不是什么，还没有达成共识。我将使用我之前设计的方法，通过分析这些生物是如何生长和发展的，来研究它们的亲缘关系。我还将通过实地考察和研究博物馆藏品的结合，建立兽形类与其他动物的进化轨迹（如果合适的话），以确定它们何时停止创新（改变它们的身体结构）以及何时灭绝。海绵通常被认为是最古老的动物谱系，但被广泛接受的最古老的海绵体化石只是寒武纪的。然而，有一些假定的埃迪卡拉纪海绵可能会在某种程度上扩展化石记录，更符合分子的预期。我将使用大型照片数据集和新的和未发表的现场标本重新检查这些化石的形态，以评估它们是否可能代表古代海绵。我还将使用计算流体动力学——一种模拟生物体周围流体流动的技术——来评估这些化石的解剖结构是否允许它们像活海绵一样发挥作用。如果这些化石中有任何可能是古代海绵，我将把它们与其他更年轻的海绵化石一起纳入形态学系统发育分析，以了解海绵生命之树。然后，我将把这些解剖和化石年龄数据与DNA数据结合起来，建立最严格的海绵年龄估计。3)我将把上述数据与之前收集到的埃迪卡拉动物群的其他成员和刺胞动物（包括海葵、珊瑚和水母）的数据结合起来，看看在前寒武纪晚期（埃迪卡拉纪），非两侧动物的解剖变化速度是否确实更快，或者是否符合寒武纪大爆发假说的预期。