How much does Chemotaxonomy help to resolve the overrepresented Cycadolepis Saporta (Bennettitales)? A case study of the Cretaceous of Patagonia, Argentina

LAFUENTE DIAZ, MAITEN A.; DEL FUEYO, GEORGINA M.; D'ANGELO, JOSÉ A.; CARRIZO, MARTÍN A.

REVIEW OF PALAEOBOTANY AND PALYNOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2021

0034-6667

The spectroscopic characterization of fivespecies belonging to Cycadolepis Saporta is used to obtain newinsights into the utilization of functional groups as chemotaxonomicparameters. The Cycadolepis spp. remains,collected from the SpringhillFormation (Hauterivian-Barremian; Santa Cruz Province, Argentina), are sterilescale-leaves, which are interpretedto be part of a hypothetical megasporangiate cone of the OrderBennettitales. Thematerials consist of five scale-leaves with very well-preserved cuticles, whichare studied by means of Fourier Transform Infrared (FTIR) spectroscopy. For this purpose, two sample forms aredefined: 1) compressions), and 2) cuticles. The semi-quantitative derived dataare evaluated through Principal Component Analysis (PCA) revealing thefunctional groups preserved for each Cycadolepistaxon. The PCA results indicate thatthe Cycadolepis spp. show similar chemical compositions regardless ofthe taxon, whereas the cuticle chemistry reveals a relatively high contributionof aromatic structures and variable contribution ofoxygen-containing compounds. The latter is presumably a consequence ofmainly phenylpropanoids and aromatic domains composing biomacropolymers. TheIR-data reveal slight differences among the five species of Cycadolepis despite the distinctivemorpho-anatomical patterns shown by the epidermis of each taxon. However,although preliminary, the first analysis of functional groups as anadditional taxonomic parameter to those morphoanatomical are encouraging andcontribute to a better understanding of the chemical composition and the probable relationship of the fivePatagonian species of Cycadolepis, a genus which is known by itspeculiar variability. Couldthese results suggest that some of the five species of Cycadolepis belong to a unique megasporangiate cone?