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

Abstract

The spectroscopic characterization of five species belonging to Cycadolepis Saporta is used to obtain new insights into the utilization of functional groups as chemotaxonomic parameters. The Cycadolepis spp. remains, collected from the Springhill Formation (Hauterivian–Barremian; Santa Cruz Province, Argentina), are sterile scale-leaves, which are interpreted to be part of a hypothetical megasporangiate cone of the Order Bennettitales. The materials consist of five scale-leaves with very well-preserved cuticles, which are studied by means of Fourier Transform Infrared (FTIR) spectroscopy. For this purpose, two sample forms are defined: 1) compressions), and 2) cuticles. The semi-quantitative derived data are evaluated through Principal Component Analysis (PCA) revealing the functional groups preserved for each Cycadolepis taxon. The PCA results indicate that the Cycadolepis spp. show similar chemical compositions regardless of the taxon, whereas the cuticle chemistry reveals a relatively high contribution of aromatic structures and variable contribution of oxygen-containing compounds. The latter is presumably a consequence of mainly phenylpropanoids and aromatic domains composing biomacropolymers. The IR-data reveal slight differences among the five species of Cycadolepis despite the distinctive morpho-anatomical patterns shown by the epidermis of each taxon. However, although preliminary, the first analysis of functional groups as an additional taxonomic parameter to those morphoanatomical are encouraging and contribute to a better understanding of the chemical composition and the probable relationship of the five Patagonian species of Cycadolepis, a genus which is known by its peculiar variability. Could these results suggest that some of the five species of Cycadolepis belong to a unique megasporangiate cone?