Extinction and survival at the dawn of plant life on land

The lycopsids are one of the earliest plants, appearing around 425 MYA. From their origins in the Silurian and through into the Carboniferous, the lycophytes were the most diverse and complex plants on Earth, and by the Carboniferous period, formed vast forests. Significant to this study is the split which occurred over the end Silurian and early Devonian, where the lycophytes diverged into two, broad groups, the zosterophylls and the lycopsids. By the end of the Devonian the zosterophylls had all gone extinct whereas the lycopsids thrived and survive through to the present day. It is unclear where or at what point the zosterophylls started to decline, or the fundamental drivers behind it, and in examining this question, our aim is to increase our understanding of the environmental pertubations during the end Devonian, as well as predict which modern forms have a higher propensity for extinction. By comparison to their Palaeozoic heyday, modern lycophytes make up only a small percentage of overall biomass and given their water dependant life cycle may be at higher risk due to human-induced changes to the biosphere.

The lycopsids are the most complex plant described within the Devonian Rhynie Chert flora, with clear root-bearing organs, as well as leaves and shoots, acquired from simpler ancestors. However, despite the Rhynie Chert being a crucial site for palaeobotany, the history of the lycopsids requires further study, including why they branched off from their sister group, the zosterophylls and what ultimately led to the zosterophylls demise. Sites of exceptional preservation such as the Rhynie Chert have enabled us to establish the origin and evolutionary history of the first vascular plants, and there is much more that it and other sites can tell us about early life on land. With modern, digital modelling techniques allowing detailed reconstructions of extinct forms, the use of cutting-edge imaging techniques such as confocal laser scanning microscopy and advancements in phylogenetic analysis, this an exciting time to be studying early plants and their evolutionary history.