ATR-FTIR SPECTROSCOPY REVEALS THE PRESERVED CHEMISTRY OF THE CONIFER PSEUDOFRENELOPSIS DINISII FROM THE LOWER CRETACEOUS (SANTA SUSANA FORMATION) OF WESTERN PORTUGAL

LAFUENTE DIAZ, MAITEN A.; DEL FUEYO, GEORGINA M.; MENDES, MÁRIO M.

General Roca, Río Negro

Jornada; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA 2023; 2023

Asociación Paleontológica Argentina

Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflectance (ATR)mode is used to analyze for the first-time foliar remains assigned to the coniferPseudofrenelopsis dinisii Mendes et Kvaček (Cheirolepidiaceae) from the LowerCretaceous (late Valanginian–early Hauterivian) of the Santa Susana Formation,Lusitanian Basin, western Portugal. The materials comprise twenty-eight foliarcompressions with well-preserved cuticles housed in the palaeobotanical collection of theGeological Museum of Lisbon, Portugal (P1183-P1210). The P. dinisii compressionswere cleaned using hydrofluoric acid (HF) and washed in distilled water to removesedimentary rock remains. The treated compressions were divided into cuticles (Ct) andcompressions (Cp; cuticles + mesophyll). The Ct samples were spectroscopicallyanalyzed without additional treatment while to obtain the Cp samples the compressionswere powdered. Semi-quantitative data (area ratios), derived from the identifiedfunctional groups (i.e., characteristic ensembles of atoms) in the spectra, were statisticallyanalyzed by principal component analysis (PCA). In this PCA, P. dinisii is statisticallyevaluated together with the previously reported spectroscopic data derived from anotherCheirolepidiaceae recovered from the same fossiliferous locality: Frenelopsis teixeiraeAlvin et Pais (P1063, P1065-P1066, P1068-P1069, and P1071-P1082). For both fossiltaxa, results indicate intraspecific variability which is interpreted as reflecting therelatively variable morphological cuticular features (e.g., trichomes: hairs and papillae)and chemical compositions of the cutins, cutans, and phenolic compounds. The Ctsamples of P. dinisii and F. teixeirae are chemically equivalent showing similarcontributions of carboxyl/carbonyl groups (C=O cont) and aromatic carbons (C=C cont)and aliphatic group intensities (‘A’ Factor). The P. dinisii Cp samples have slightly higherC=C cont values and lower ‘A’ Factor values than the cuticles of P. dinisii and F. teixeirae.This fact is mainly related to the presence of lignified tissues (aromatic structures) in themesophyll (e.g., vascular bundles and hypodermal cell remains). The chemical similaritybetween both fossil taxa could be a consequence of the particular chemical compositionof the Cheirolepidiaceae family. On the other hand, the compressions of P. dinisii and F.teixeirae could have been affected in fossil diagenesis at the fossiliferous level resultingin fossil materials sharing a similar chemical composition. Further spectroscopicalanalysis of other cheirolepidiaceous fossil taxa from Portugal are needed to evaluate thefactors (systematic or taphonomic) that could be affecting the cuticular chemistry of theseextinct conifers.