Sprecher
Beschreibung
Acritarchs are an important component of Palaeozoic (micro-)fossil assemblages. Although they are commonly regarded as phytoplankton, their biological affinities are by definition unknown, and consequently their exact role in ancient ecosystems is uncertain as well. Some acritarchs from the Cambrian onwards show similarities with certain cysts of dinoflagellates, which today are one of the major phytoplankton groups but are only unequivocally known since the Triassic. It seems likely that some acritarchs represent precursors of this group but lack key characteristics of dinoflagellate cysts, such as paratabulation, a cingulum or an archaeopyle. Molecular clocks and organic geochemical analyses also support the presence of dinoflagellates in the early Palaeozoic. We aim to elucidate the biological affinity of acritarchs through the systematic study of acritarchs and dinoflagellates in terms of morphology and palaeobiochemistry. We use Fourier-transform infrared (FTIR) spectroscopy for chemotaxonomy alongside morphological comparisons to test possible phylogenetic relationships. Through the infrared spectra of isolated specimens, different biopolymers and ratios between functional groups can be identified. This provides evidence for both biological affinities and diagenetic alterations. The studied material comes from various Palaeozoic deposits with low thermal maturity, such as the Lower Silurian Visby beds of Gotland, Sweden. Here, a wide variety of both stratigraphically constraint and long-ranging, widely occurring acritarch taxa (e.g., Diexallophasis, Domasia, Micrhystridium, Multiplicisphaeridium, Veryhachium, Visbysphaera) are analysed along with forms that are commonly considered to represent prasinophycean algae, such as Cymatiosphaera and Dictyotidium.