Origin and early diversification of vascular plants: integrating evidence from the plant megafossil and dispersed spore fossil records

在地球历史的大部分时间里，大陆基本上是贫瘠的。即使在寒武纪大爆发之后，当海洋开始充满复杂的动物生命时，地球表面也没有生命。最终，大约4.6亿年前，第一批陆地植物进化出来了。光合作用植物第一次生长在陆地表面。这是地球生命史上的一个重大事件，主要有三个原因：(i)它代表了第三个多细胞生命王国的进化（植物加入真菌和动物）。（ii）它为其他生物入侵陆地铺平了道路，包括蠕虫、昆虫，最后是我们的直系祖先（第一批两栖动物）。它对地球环境产生了巨大影响，改变了大气成分和气候、土壤形成模式、侵蚀、风化、沉积等。这个研究项目的目的是通过对植物化石的研究来阐明植物对土地的入侵。它将集中于石松类。这些是现存植物中最原始的一组，包括一些我们熟悉的植物，如石松属和卷柏属。石松类的丰富化石记录可以追溯到4亿多年前。化石要么是整株植物（巨化石），要么是植物在生命过程中释放出来的孢子（分散的孢子）。巨型化石很罕见，解释它们的化石记录很困难。然而，幸运的是，植物在一生中产生并释放出数十万个微小的孢子。这些孢子被风广泛传播，然后降落在潮湿、肥沃的土壤上，长成新的植物，或者更常见的是，沉积在湖泊、河流或海洋中。后者变成沉积物，很容易变成化石。因此，我们可以溶解古代湖泊、河流和海洋沉积物，并恢复古代植物产生的孢子。本项目旨在整合石松类巨化石和分散孢子化石记录，以揭示植物入侵土地的历史。新发现的仍含有孢子（原位孢子）的石松巨型化石将被研究，以表征石松孢子的性质（这将与对活石松孢子特征的研究一起进行）。然后，我们将研究丰富的分散孢子记录，以确定第一批石松是何时进化的，它们是如何多样化（通过进化）并在大陆上传播的。这也将为理解早期植被进化和传播过程中发生的复杂环境变化提供一个空间/时间模板，希望能对当前全球变化有关的问题有所启示。

For most of earth history the continents were essentially barren. Even following the Cambrian explosion, when the oceans began to teem with complex animal life, nothing lived on the planet surface. Eventually, some 460 million years ago, the first land plants evolved. For the first time photosynthesizing plants grew on the land surface. This was a monumental event in the history of life on earth for three main reasons:- (i) It represented the evolution of the third kingdom of multicellular life (plants joined the fungi and animals). (ii) It paved the way for other organisms to invade the land, including the worms, insects and finally, our direct ancestors (the first amphibians). (iii) It had a dramatic effect on the environment of planet earth, altering atmospheric composition and climate, patterns of soil formation, erosion, weathering, sedimentation etc. The aim of this research project is to shed light on the invasion of the land by plants through the study of fossil plants. It will concentrate on lycopsids. These are the most primitive group of living plants, and include some familiar plants such as Lycopodium (clubmosses) and Selaginella. The lycopsids have a rich fossil record stretching back more than 400 million years. The fossils occur either as whole plants (megafossils) or spores that were released by the plants during life (dispersed spores). Megafossils are rare and interpreting their fossil record is difficult. Fortunately, however, plants produce and release hundreds of thousands of minute spores during a lifetime. These spores are widely dispersed by the wind before either landing on damp,fertile soil and growing into a new plant, or more commonly, being deposited in lakes, rivers or the sea. The later become incorporated into sediments and are easily fossilized. Thus we can dissolve up ancient lake, river and marine deposits and recover the spores produced by ancient plants. The aim of this project is to integrate the lycopsids megafossil and dispersed spore fossil records to shed light on the invasion of the land by plants. Newly discovered lycopsid megafossils that still contain spores (in situ spores) will be studied to characterise the nature of lycopsid spores (this will be done in conjunction with a study of spore characters in living lycopsids). We will then examine the rich dispersed spore record to ascertain when the first lycopsids evolved, how they diversified (through evolution) and spread across the continents. This will also supply a spatial/temporal template for understanding the complex environmental changes that occurred as the early vegetation evolved and spread, hopefully shedding light on issues concerned with current global change.