Cambrian Nervous Systems for Reconstructing the Arthropod Tree of Life

节肢动物是一种无脊椎动物，有外骨骼、分段的身体和关节的腿，如昆虫、螃蟹、蜘蛛和蜈蚣。到目前为止，节肢动物门是最大和最多样化的门，与两个较小的门--金鱼纲(天鹅绒蠕虫)和缓步动物(水熊)--密切相关，共同形成了泛节肢动物门。它们最早出现在5.2亿年前的“寒武纪大爆发”中，标志着化石记录中大多数主要动物门的突然出现。盘足类具有悠久的地质历史和特殊的多样性，是了解动物起源和早期演化的理想对象，因此研究它们的寒武纪化石记录是基础。盘足类外表的巨大多样性使它们之间的相互关系难以理解。相比之下，最近的研究表明，中枢神经系统(CNS)的进化非常保守，虽然物种之间可以识别出差异，但每个主要类群内的总体安排一直非常稳定。因此，CNS为了解主要的盘足类群之间的关系提供了一个主要的数据来源。不幸的是，现存物种不能告诉我们最早的泛节肢动物大脑和神经系统，或者它们的早期进化史。只有记录了节肢动物进化最早阶段的化石才能提供答案。动物柔软的部分在死亡后往往会迅速腐烂，因此大多数节肢动物化石是坚硬部分(如外骨骼)的遗骸，对它们的内部解剖知之甚少。然而，在特殊情况下，生物的未矿化软组织也可以被保存在精细的细节中，例如在两个著名的寒武纪化石组合中：中国西南部的澄江生物群(约520 Mya)和加拿大伯吉斯页岩(约505 Mya)。这两种化石都产生了丰富的泛节肢动物化石，外部形态和内部解剖都保存得非常完好，提供了关于最早的泛节肢动物的关键信息。与神经组织经不起石化的传统假设相反，申请人和她的同事最近报告了澄江节肢动物的大脑和神经系统异常保存的情况，这为了解节肢动物化石注入了新的数据，并建立了一个新的研究领域-神经古生物学。进一步的临时研究在更早的化石中发现了大脑和其他神经组织，为节肢动物大脑的起源提供了重要信息；以及在寒武纪节肢动物中发现了保存异常完好的循环系统(以前在节肢动物化石记录中几乎是未知的)和感觉结构(例如眼睛和触角上的感官)的新发现。本项目的目的是准确地记录澄江和布尔吉斯页岩生物群中保存完好的寒武纪泛节肢动物(如叶足类、异足类和节肢动物)的中枢系统、感觉结构和其他内部器官系统，并将这些数据与生活群体进行比较，以增加我们对辐射和分歧早期主要类群之间进化关系的了解。

Arthropods are invertebrate animals with an exoskeleton, a segmented body, and jointed legs, such as insects, crabs, spiders and centipedes. Arthropoda is by far the largest and most diverse phylum today and is closely related to two smaller phyla, Onychophora (velvet worms) and Tardigrada (water bears), together forming Panarthropoda. They first appear 520 million years ago (Mya) in the "Cambrian Explosion", marked by the sudden appearance of most major animal phyla in the fossil record. The long geological history and exceptional diversity of panarthropods make them ideal candidates for understanding the origin and early evolution of animals, and it is thus fundamental to investigate their Cambrian fossil record.The great diversity in the external appearance of panarthropods makes it difficult to understand their interrelationships. In contrast, recent studies show that the evolution of the central nervous system (CNS) has been remarkably conservative, and while variations between species can be recognised, the general arrangement within each major group has been very stable. Therefore, the CNS provides a primary source of data for understanding the relationships of major panarthropod groups. Unfortunately, extant species cannot inform us about the earliest panarthropod brains and nervous systems, or their early evolutionary history. Only fossils, which record the earliest stages in the evolution of arthropods, can provide the answers.Soft parts of animals tend to decay away quickly after death, so most arthropod fossils are the remains of hard parts (e.g. exoskeletons) and much less is known about their internal anatomy. However, under exceptional circumstances, the unmineralised soft tissue of organisms can also be preserved in exquisite detail, such as in two famous Cambrian fossil assemblages: the Chengjiang biota, southwest China (circa 520 Mya), and the Burgess Shale, Canada (circa 505 Mya). Both yield abundant panarthropod fossils with exceptionally preserved external morphology and internal anatomy, providing crucial information about the earliest panarthropods. Countering orthodox assumptions that neural tissue does not withstand fossilization, the applicant and her colleagues recently reported exceptionally preserved brains and nervous systems from Chengjiang arthropods, which added a fresh injection of data for understanding fossil arthropods and established a new research field, "neuropalaeontology". Further provisional studies have discovered the brain and other neural tissues in even earlier-derived fossil panarthropods, providing vital information regarding the origin of arthropod brains; as well as new discoveries of exceptionally preserved circulatory systems (previously all but unknown in the arthropod fossil record) and sensory structures (e.g. eyes and sense organs on the antennae) from Cambrian panarthropods. Together with their CNS, these provide unique insights into the ecology and evolution of early panarthropods.The aim of this project is to accurately document the CNS, sensory structures and other internal organ systems from exceptionally preserved Cambrian panarthropods (e.g. lobopodians, anomalocaridids and arthropods) of the Chengjiang and Burgess Shale biotas and compare the data with living groups, so as to increase our understanding of the evolutionary relationships between major groups during the early stages of radiation and divergence.