The transition between the Jurassic (201-145 million years ago) and Cretaceous (145-66 million years ago) represents a pivotal moment in the history of life on Earth. The rise of flowering plants around 130 million years ago drastically changed terrestrial ecosystems, potentially leading to the rise in diversity of insects, mammals, and other animal groups. This led to the birth of our modern world. However, the causes and context for the rise of flowering plants are still hotly debated and mostly unknown. On the one hand, the rapid climatic changes during that period could have created new condition for the flowering plants to flourish. On the other, the decline of the pre-existing vegetation might have left some empty ecological possibilities that the flowering plant could then exploit. Another view sees the flowering plants outcompeting their naked seed (gymnosperm) relatives, thanks to their novel advantageous traits such as fruits or more efficient leaves. Moreover, these abiotic and biotic factors might have interacted in complex ways to lead to these outcomes.
Our project plans to understand the context of the rise of the angiosperms by looking at the dynamics of the plants that were dominant before and during their period of diversification and rise, namely the gymnosperm groups cycads, conifers, and Gnetales. These groups are too often misunderstood as living fossils, with a long, static evolutionary history that saw them declining because of the competition of the more advanced flowering plants. Is this really the case?
We plan to reconstruct the evolutionary history of these three groups to identify the relationships of fossil and extant plants. We will leverage the availability of DNA sequences from extant species and a careful investigation of the morphology of extant and fossil plants to generate phylogenetic trees using state-of the art statistical methodologies that integrate the uncertainty over ages and diversification histories. This is vital when dealing with the vagaries of the fossil record. These trees will then help us to understand how the rates of speciation and extinction through time, as well as the patterns of morphological diversification, changed across the three gymnosperm groups during the Jurassic-Cretaceous transition. The shared patterns across these groups, as well as the more idiosyncratic ones, will be compared with the timing and scale of the climatic oscillations of the period, as well as with the increase of angiosperm diversity starting in the Early Cretaceous. This will help us understand the causes of this major worldwide floristic transformation, and help us to point towards possible challenges to the global flora caused by current and future climatic changes.