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

动物的崛起是生命史上的一个深刻转变;生物第一次能够设计周围的环境，改变地球化学循环，构建复杂的生态系统并多样化为无数形式。然而，动物的崛起也是地球历史上最具争议的事件之一。在寒武纪时期--所谓的“寒武纪大爆发”--化石记录中出现了大量可识别的动物，但达尔文的自然选择进化论要求动物有更长的进化历史，一直延伸到前寒武纪（4000 - 5.39亿年前）。事实上，来自DNA的数据也表明动物的前寒武纪根很深，这种不匹配变得更大，我们越接近动物树的根，例如，海绵起源的遗传估计与该群体公认的化石记录之间的不匹配是数亿年的数量级。我打算通过研究这些特别古老的谱系，比如海绵，来更好地限制动物的起源和多样化。大多数研究关注这个问题，倾向于关注左右对称的动物，但更古老的非左右对称谱系，由于其更大的年龄，可能有更长的化石记录，一直没有得到充分的研究。这一提议试图通过实现三个不同的研究目标来纠正平衡：1）埃迪卡拉纪（最新的前寒武纪）大型生物群，出现在大约5.7亿年前的化石记录中，是一组具有长期灭绝体型的生物，但越来越多的证据表明，其中至少有一些代表古代非两侧对称动物的遗骸。由于它们奇怪的解剖结构，它们通常不被包括在动物早期进化史的研究中，因此仍然是房间里的大象。我打算研究埃迪卡拉纪最年轻的大型生物群--erniettomorphs --这是一组由连续重复的管道组成的生物体--也是最神秘的生物之一，关于它们是什么，或者说不是什么，没有共识。我将通过分析这些生物如何生长和发育来研究它们的亲和力，使用我以前设计的方法。我还将通过实地工作和研究博物馆藏品的结合，建立与其他动物相关的erniettomorphs的进化轨迹（如果合适的话），以确定它们何时停止创新（改变它们的体型）以及何时灭绝。2）海绵通常被认为是最古老的动物谱系，但最古老的被广泛接受的海绵体化石的年龄只有寒武纪。然而，有一些假定的埃迪卡拉纪海绵可能会在某种程度上延长化石记录，更符合分子预期。我将使用大型照片数据集和新的和未发表的野外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。如果这些化石中的任何一个可能是古代海绵，我将把它们包括在形态系统发育分析中，以了解海绵生命树，以及其他更年轻的海绵化石。然后，我将把这些解剖学和化石时代的数据与DNA数据结合起来，以建立对海绵年龄的最严格估计。3)我将上述数据与先前收集的埃迪卡拉纪大型生物群和刺胞动物（包括海葵，珊瑚和水母）的其他成员的数据相结合，以询问非两侧动物的解剖变化率是否确实在前寒武纪晚期（埃迪卡拉纪）更快，或者符合寒武纪爆炸假说的预期。

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.