Chemical characterization of Cycadolepis scale-leaves from the Springhill Formation (Lower Cretaceous, Argentina).

DIAZ, MAITEN A. LAFUENTE; DEL FUEYO, GEORGINA M.; D`ANGELO J A; CARRIZO, MARTÍN A.

Workshop; 1° Reunión Virtual de Comunicaciones de la Asociación Paleontológica Argentina; 2020

Scale-leaves of Cycadolepis spp. (Bennettitales) are analyzed for the first time by Fourier Transform Infrared (FTIR) spectroscopy revealing mesophyll and cuticle preserved functional groups. The latter are used to characterize five potential species with the aim of evaluating the functional groups as potential chemotaxonomic parameters. The material consists of five incomplete scale-leaf compressions with well-preserved cuticles (MPM-PB 15341-15345), from the Springhill Formation (Hauterivian-Barremian; Santa Cruz, Argentina). For the spectrometric study, scale-leaves were analyzed into two sample forms: compressions (including coalified mesophyll and cuticle) and cuticles. In turn, one specimen was differentiated into apical and basal parts (MPM-PB 15343). Semiquantitative IR-data were evaluated using principal component analysis. The results indicate that compressions have a similar chemical composition among specimens and scale parts with a low contribution of aromatic carbon compounds. In contrast, the tcutiicles show high variability. Particularly, the variation of oxygen-containing compounds could be due to the chemical composition of cutin/cutan and other constitutive compounds of the cuticle. Additionally, the presence of diverse trichomes (hairs, papillae, and idioblasts) could contribute to the variability of the cuticle sample form. On the other hand, no distinctive differences among the specimens were recognized. In this case, the intraspecific variability among the specimens, which is denoted in cuticular features, could hamper the use of functional groups as additional taxonomic parameters to those morphoanatomical. Although preliminary, these results are encouraging and contribute to a better understanding of the chemical composition of five Patagonian species of Cycadolepis, a genus known by its peculiar variability.