Sprecher
Beschreibung
The phylogenetic placement of unicellular microfossils is commonly impeded by limited diagnostic morphology. This leads to ever-expanding informal “wastebasket” taxa—such as acritarchs (Eukaryota; >10k species with predominantly Paleozoic occurrences)—with restricted evolutionary value. Vibrational spectroscopy-based chemotaxonomy offers a promising yet underexplored alternative for acritarch placement through organic wall biosignature matching with known clades. Here, we establish a chemotaxonomic framework applicable in deep time based on an unprecedented infrared spectroscopy dataset of >500 Ordovician–Quaternary unicellular eukaryotic palynomorphs, including phycomata of prasinophyte green algae, dinoflagellate cysts, bisaccate pollen, trilete spores, and acritarchs.
Using single-specimen attenuated total reflection, and transmission Fourier transform infrared microspectroscopy (µ-FTIR), we systematically track diagenetic and catagenetic transformations of the lineage-specific wall biopolymers—algaenan (green algae), dinosporin (dinoflagellate cysts), and sporopollenin (plant pollen and spores)—across modern, experimentally matured, and fossil material. Despite progressive macromolecular homogenization driven by temperature-induced defunctionalization and aromatization, phylogenetically informative spectral features survive fossilization and enable robust discrimination between biopolymer classes.
Paleozoic acritarch biosignature matching reveals affinities with green algae and dinoflagellates, demonstrating acritarch polyphyly and providing the first direct macromolecular evidence for pre-Triassic dinoflagellates facilitating the resolution of a >200 million year ghost lineage predicted by molecular clocks. These results demonstrate that µ-FTIR can be applied to decode the hidden diversity and deep evolutionary history of extinct unicellular eukaryotic life. Our methodological approach, when applied at a broader scale, allows to effectively counter the expansion of wastebasket taxa, as well as map out the fate of organic matter in the fossil record.