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

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.