TEM and EDS characterization in a Bennettitalean cuticle from the Lower Cretaceous Springhill Formation, Argentina

Abstract

New cuticle samples from the bennettitalean Ptilophyllum eminelidarum were herein studied using the combination of light microscopy (LM), scanning and transmission electron microscopy (SEM, TEM), and element analysis by Energy Dispersive Spectroscopy (EDS). The new TEM studies correspond with and improve the former ones; however, statistical measurements reinforce their uniqueness and erect Bennettitales as a heterogeneous group of cuticles. Six types of cuticles were recognized. According to the factorial component analysis (FCA), the cuticles of the stomatal apparatus show the highest level of interest, while the epidermal cell cuticles, the lowest. For the 9 variables, the top 6 as to importance were the most independent, which could be used as criteria for identification in Bennettitales. A dichotomous key was built, allowing for a rapid identification of each of the 6 types of cuticles based on the 9 variables. Showcasing an upper cuticle significantly thicker and more exposed, and a thinner lower cuticle that is normally more protected, the micropalaeoenvironment of these leaves is of interest. The taxonomical identity of the present taxon is also revealed by the EDS values; S/Ca ratio is homogeneous for all layers of both cuticles, leading to assume, with extreme precaution, a putative similar influence of the palaeoenvironment on these two opposite surfaces of the leaf. As the first detailed statistical TEM and EDS for the Bennettitales, it highlights the great interest of this type of studies and the strong interest for revealing the characters of each type of cuticle and layer.