Chemometric study of structural groups in medullosalean foliage (Carboniferous, fossil Lagerstätte, Canada): Chemotaxonomic implications

Abstract

A larger chemometric study (data derived from Fourier transform infrared spectroscopy-FTIR interpreted by principal component analysis) is undertaken involving species (numbers bracketed) from the four medullosalean families Neurodontopteridaceae (7), Potonieaceae (1), Cyclopteridaceae (1), and Alethopteridaceae (1). Samples originated from the fossil Lagerstätte ("medullosalean forest") in the Late Pennsylvanian of Sydney Coalfield, Nova Scotia, Canada, where they are preserved as compressions or fossilized-cuticles. The study aims at demonstrating how the level of objectivity for medullosalean fossil-plant determinations can be raised through inquiring (i) if the chemistry of isolated foliage supports the specific classification based on morphologies alone, (ii) if chemistry of different preservation states hampers the application of chemometrics, and (iii) if taxonomic assignation of poorly preserved specimens can be assisted by chemometrics. Given the similar thermal history, direct chemical comparisons amongst taxa having the same preservation state were possible. The chemometric approach resulted into a two principal-component model (80% cumulative-explained variance) that provided information on the relative contributions of aromatic structures, oxygen-containing, and aliphatic groups. These functional groups enabled statistical distinction amongst most of the morphology-defined species, and families, irrespective of the two preservation states. We concluded that results, overall, support the aims of the study, with implications to solve some palaeobotanical difficulties related to biostratigraphy and palaeobiogeography.