Chemotaxonomic classification of Pennsylvanian fossil plants using Fourier transform infrared spectrometry evaluated through principal component analysis

D`ANGELO, J A; ZODROW, E L; CAMARGO, A

Mar del Plata, Argentina

Simposio; XIV Simposio Argentino de Paleobotánica y Palinología; 2009

Well-preserved gymnosperm fossil plants from the Pennsylvanian of Sydney, Nova Scotia, Canada were studied by means of semi-quantitative Fourier transform infrared spectroscopy (FTIR) and evaluation through Principal Component Analysis (PCA). Studied samples included coalified compressions, fossilized cuticles and cuticles obtained by chemical maceration. Selected taxa, namely Alethopteris pseudograndinioides Zodrow et Cleal 1998, A. ambigua (Lesquereux pars) Zodrow et Cleal 1998, Macroneuropteris scheuchzeri (Hoffmann) Cleal et al. 1990 (foliage), Trigonocarpus grandis (Lesquereux) Cleal et Zodrow 2009 (seed-fern ovule) and Cordaites principalis (Germar) Geinitz 1855 (foliage) were investigated to assess whether their chemical compositions can be used in chemotaxonomic comparisons. Some coal macerals and coal samples from the same sequence were included for comparative purposes. In this experimental study, Schulze’s chemical process was used to liberate plant cuticles from suitably preserved coalified compressions by oxidation in an acid solution (maceration), followed by an alkaline treatment. These solutions were studied by liquid-state FTIR analysis using attenuated total reflectance technique. FTIR-derived data from all the sample forms were subjected to PCA to evaluate the grouping of data as a function of their chemical structure (functional groups). Results of the PCA analysis allowed for the identification of groups related to the modes of preservation and, most importantly, to taxa traditionally defined by morphology. A subset of samples, including only compressions, coals, and vitrinites was subjected to PCA in order to obtain a better discrimination of the data. This was useful for the determination of the chemosystematic differences among the genera studied. These findings increasingly support our hypothesis that FTIR-derived data from Pennsylvanian fossil leaves have chemotaxonomic utility.