Paleontological sites are like keyholes into the past, through which we can look at former ecosystems and reconstruct their species composition, complexity and dynamics. Most sites, however, have one fundamental disadvantage: plant and animal macrofossils require entirely different conditions to be preserved. Therefore, even at sites with rich faunal assemblage, the flora is usually left in the dark. Commonly, the vegetation is then only inferred indirectly from faunal composition or the animals’ adaptions to specific vegetation types.
But even at sites without plant macrofossils, direct access to the vegetation can be provided by inorganic formations of the plants: phytoliths.
These phytoliths, literally ‘plant stones’, are microscopically small (2-250µm) three-dimensional, mineral particles (e.g. silica, calcium oxalate), which are produced and deposited by living plants within their cell walls, intercellular spaces and lumina. As inorganic structures, phytoliths are very resistant to decay and weathering, and represent the most enduring of all known plant fossils. They become microfossils of their producer and remain identifiable over after their release from the plant tissue.
Size and shape of these ‘plant stones’ differ greatly between the plant species that produce them. The shape of phytoliths is of particular importance: the morphology of these inorganic bodies seems to be genetically determined and can thus be specific for a particular plant family, genus, or even species. Fossil phytoliths therefore directly indicate the occurrence of a particular plant family, genus, or species at a given location and time. Thus, we can use the composition of fossil phytolith assemblages to directly analyse local plant communities and how they changed through time.
Thanks to their durability, phytoliths can be isolated from sediments that would normally provide unfavourable conditions for plant preservation (albeit such conditions are generally ideal for animal preservation). Thereby, phytoliths can close the preservational gap of plant fossils at vertebrate fossil sites.
During their formation, phytoliths can encapsulate parts of the cell wall or other cell material. In such cases it is possible to isolate ‘occluded carbon’ from inside the phytoliths. Such enclosed and thereby protected carbon can be used for dating and calculating δ13C values, which shed light on the photosynthetic pathway of the original plant. Moreover, phytoliths can be used to determine δ18O values, since ground water is incorporated in silica formation.
In order to assign fossil phytoliths to a particular group of plants, a comparison with recent plants is required. Therefore, in addition to examining fossil phytoliths, the establishment of a comparative recent phytolith collection represents a major focus of this project.
Of particular interest is the Upper Miocene vegetation, especially the spread of C4 grasses during this period. On the basis of fossil sites in the Middle East and southeastern Europe, we pursue the advance of C4 grasses in the Upper Miocene and examine in detail the possible causes of this fundamental vegetational shift.