CONICET | Buscador de Institutos y Recursos Humanos

Leaves of Pseudoctenis ornata (Cycadophyta) are chemically analyzed for the first time by semi-quantitative Fourier Transform Infrared (FTIR) spectroscopy. The FTIR-derived data are compared with those obtained from Squamastrobus tigrensis leaves (Podocarpaceae). The specimens are compressions with cuticular features very well-preserved coming from the renowned Baqueró Group (Aptian, Santa Cruz, Argentina). Pseudoctenis ornata (BAPb 1217, 1220, 1222) was collected from Punta del Barco Formation at Estancia El Verano locality, while S. tigrensis (BAPb 7678, 11321, 11324, 11333, 11583-11586) comes from Anfiteatro de Ticó Formation at Bajo Tigre locality. The aim of this contribution is to reveal mesophyll and cuticle chemical structures (functional groups) of these two gymnosperm fossil taxa that underwent to volcanic setting influence. The spectrometric study was carried out analyzing two sample forms: (1) compressions (including coalified mesophyll and cuticle) and (2) cuticles. The latter were obtained from compressions by maceration. The FTIR-derived data were statically evaluated by principal component analysis (PCA). In general, P. ornata has the highest aliphatic nature. This is probably a consequence of micromorphological features (cuticle thickness and papillae) and cutin composition (monomer types and their relative contents). On the other hand, S. tigrensis compressions show, in most samples, longer and straight aliphatic chains than their respective cuticles. These results are probably related to the fact that both fossil taxa are preserved as fossilized cuticles (i.e., compressions having a certain degree of natural oxidation). This is most likely attributed to the intense volcanic activity and cold ash falling occurred during the Aptian sedimentation in Patagonia.