最古老的有头类及其近亲

《The Origin of Species》 and 《The Decent of Man》by Ch. Darwin have been fundamentally changing the world-outlook of majority of scientists. The former has built up the evolutionary theory with the idea of “the tree of life” as its core; and the latter declared that humankind has been evolved from lower animals. During the long magnificent evolutionary journey, one of the most significant creative event should be transition from acraniates to the craniates. As a result, the remote ancestor of Man, for the first time, created his brain, eyes the primitive vertebrae and other key organs. Luck enough, the oldest-known craniates, so-called “the first fish” Myllokunmingida, including Myllokunmingia, Haikouichthys and Zhongjianichthys, have been discovered from the early Cambrian Chengjiang fossil Lagerstaette (treasure); and these fossil-stars of 520ma are now widely recognized as the oldest ancestor of humankind in the whole family of craniates or vertebrates. However, investigates are by no means ended. Many questions are still to be answered. Was the brain of the first fish tripartite or pentamerous? How was their eye’s structure? How did their notochord transform into the primitive vertebrae? And how were they distributed geographically in the vast area of Chengjiang fossil treasure? What is the principal distinction between controversial yunnanozoans and the true craniates? Finally, among their direct ancestors and side-branches to the ancestors of the earliest craniates, where should Cathaymyrus, Cheungkungella, Shankouclava, vetulicystids and vetulicolians be the right place in the phylogeny of lower deuterostomes? The resolution of these problems will certainly further support the evolutionary theory, and deeply answer the questions“Who I am, where I did come from”.

达尔文的《物种起源》和《人类由来》深刻改变了人们的自然观和世界观：前者构建了以“生命之树”猜想为核心的进化论，后者则宣称，人类是由低等动物逐步演化而来。在该宏伟进化历程中，最重大的一次创新当属从无头类向有头类的跃进。由此，人类远祖首次拥有大脑、眼睛和原始脊椎等关键器官。十分幸运，澄江动物群中现身的最古老有头类“第一鱼”昆明鱼目，首次将人类远祖深时探源推进到5.2亿年前。然而，探索远未终结，许多重要问题仍有待深入探究：第一鱼的脑是三分，还是五分？其眼睛的三维构造如何？它们如何完成由脊索向脊椎的转化？它们在澄江动物群广阔地域里是如何分布的？此外，备受争议的云南虫类与真正的有头类有何根本区别？在第一鱼的直系和旁系祖先中，华夏鳗、长江海鞘、山口海鞘、古囊类、古虫动物门各处于何种地位？这些难题的破解将进一步实证进化论，并对生命之树假说和人类由来思想做出重要补充，深层次地解答“我是谁，我从哪里来”。

研究背景：2009年前，舒德干团队在澄江动物群已陆续发现了所有6类早期后口动物，并构建了最早的后口动物亚界谱系演化图；期间，侯先光和陈均远等也对该亚界研究做出了部分贡献，并提出一些不同见解。于是，本项目拟对已知类群进行再研究，进一步探索该亚界中是否可能存在更原始类群、以及与后口动物演化相关的类群；力图揭示寒武纪大爆发的本质内涵；并甄别出哪些类群与人类远祖的基础器官诞生密切相关？..主要研究内容：.对约5.2亿年前的第一鱼昆明鱼目、华夏鳗、长江海鞘、云南虫类、古虫动物门、古囊类等后口动物进行了再研究；在综合分析澄江动物群、小壳生物群和埃迪卡拉晚期生物群属性的基础上，进一步论证三幕式寒武纪大爆发假说；并提出：昆明鱼目构成了包括人类在内的所有“三分体”动物（即具头脑、含脊椎的躯干、肛后尾）的鼻祖，古虫动物门则成为已知最早的初级“二分体”（具鳃裂的前体和具肠道的后体）成员，而5.35亿年前可能的微型后口动物皱囊虫构成最接近有口无肛的原始“单囊体”。.此外，还新发现了介于后口动物亚界与原口动物亚界之间的一个过渡型动物毛颚动物，发表于英国《Palaeontology》。..研究结果和意义：.比澄江后口动物更古老的“微型后口动物”皱囊虫（5.35亿年前）的研究结果以封面论文形式发表在《Nature》上，该动物“有口无肛”的独特性状显示，它接近人类和其他脊椎动物的原始“天下第一口”鼻祖，成果在西方学界和媒体引起强烈反响。.对已知后口动物的再研究、三幕式寒武纪大爆发假说求证和人类远祖基础器官诞生的论证成果，被收录于长篇中、英文论文“澄江动物群的核心价值”中（《地学前缘》，2020年）。杂志主编王成善院士为该文撰写的编者按给予高度评价：它“初步破解了达尔文留下的几个重大科学难题”；该成果受到学术界的广泛关注，多期次登上Science, PNAS 和Science Advance等网站。