ATR-FTIR spectroscopy and cuticular chemistry of the Cheirolepidiaceae Pseudofrenelopsis dinisii from the Lower Cretaceous of Lusitanian Basin, western Portugal

Pseudofrenelopsis dinisii Mendes et Kvaček, 2023 specimens, consisting of vegetative shoots recovered from the Lower Cretaceous sedimentary deposits of Santa Susana Formation in the Estremadura region of western Portugal, are chemically characterised using Fourier Transform Infrared (FTIR) spectroscopy in Attenuated Total Reflection (ATR) mode. The fossil specimens, compressions with well-preserved cuticles, were analysed to evaluate the preserved chemical composition of mostly the abaxial cuticle ( = Ct samples) and, to a lesser extent, the mesophyll ( = Cp samples). Semi-quantitative data of P. dinisii were statistically analysed together with those of Frenelopsis teixeirae Alvin et Pais emend. Mendes et al., 2010, another Portuguese cheirolepidiaceous conifer collected from the same plant-bearing bed, using principal component analysis (PCA). The results indicate intraspecific variability for P. dinisii (and F. teixeirae) cuticles, which would reflect the variable chemical compositions of the structural compounds (i.e. cutins, cutans, and phenolic compounds). The Ct samples of P. dinisii and F. teixeirae are chemically similar, in regard to the aliphatic group intensity (‘A’ Factor) but have variable contents of carboxyl/carbonyl (C = O cont) and aromatic carbons (C = C cont) groups. The P. dinisii Cp samples have the highest values of C = C cont, mainly assigned to phenolic compounds in the mesophyll (e.g. as part of vascular bundles). The chemical similarity between the cuticles of both frenelopsid taxa suggests a common chemical cuticular composition among cheirolepidiaceous (conifers). However, specific palaeoenvironmental conditions (physicogeochemical features) might have affected the P. dinisii and F. teixeirae specimens, resulting in the fossil materials converging into a similar chemical composition. Additional analysis of cheirolepidiaceous fossil taxa from Portugal is needed to evaluate the factors (systematic or palaeoenvironmental) that may influence the cuticular chemistry of these extinct conifers.