The MIOVAT (Miocene vegetation of the African tropics (project MioVAT)) initiative used fossilized pollen and spores to investigate the evolutionary history of tropical forest and savannah biomes in West Africa during the Miocene Period 23 to 5.3 million years ago. The Miocene was a critical time in the evolution of West African vegetation when grasses utilising the C4 photosynthetic pathway rapidly extended their range, giving rise to the savannahs. Researchers used acid digestion and density separation to release fossil pollen and spores from sediment samples from West Africa. These were then studied using a range of microscopy techniques. In addition, the team compiled an image library of fossil pollen and spores derived from the Palaeogene-Neogene rainforests of southern Nigeria. Pollen samples from oak (Quercus) and spruce (Picea) were imaged for the purpose of comparative microscopy work. Grass (Poaceae) from herbarium sheets and fossil grass pollen from sediment samples were imaged and used to gather data on pollen morphology across the grass family. Experiments were also conducted to compare human and computer classification of grass pollen. Researchers used computational methods to quantify the complexity of grass pollen surface ornamentation in order to study self-organised vegetation patterns in dryland ecosystems. The result was new methods for classifying pollen grains based on high-resolution imaging and computational image analyses. The comparative work carried out on oak, pine and grass pollen revealed that the combination of brightfield illumination, confocal microscopy and scanning electron microscopy increased the taxonomic resolution of pollen and spore fossil record. This increased the range and depth of hypotheses that can be tested using the fossil pollen and spore record. MIOVAT provided a new computational approach for describing 2D shapes. It also highlighted the growing concern regarding classification of biological objects using computational methods and more traditional approaches based on human analyses. Furthermore, project findings will help to explain the role of extinction in shaping the tropical vegetation of West Africa and the evolutionary success of grasses. This vital information will make a significant contribution to conserving the biodiversity of tropical forests and savannahs in the face of a changing climate.
Pollen, biodiversity, tropical forests, savannahs, Miocene, vegetation, West Africa