Fossil cutin of Johnstonia coriacea (Corystospermaceae, Upper Triassic, Cacheuta, Argentina)

Abstract

For the first time, a cutin polymer was obtained from specimens of Johnstonia coriacea (Corystospermales, Corystospermaceae) from the Upper Triassic of Cacheuta, Argentina. These are preserved as fossilized cuticles i.e., naturally macerated compressions under anoxic conditions. Laboratory oxidation reactions were used to obtain the cuticle, which after additional, long-term oxidation yielded the cutin polymer. Cutin, cuticles, and fossilized cuticles, were analyzed by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. Cutin IR spectrum was mainly characterized by intense peaks of aliphatic stretching bands at 3000–2600 cm−1, ester C=O groups centered at 1730–1715 cm−1, and aromatic C=C absorption bands at 1645–1640 cm−1. Values of semi-quantitative, IR-derived ratios of cutin were lower than those of the cuticle. The only exception was the notably higher C=O/C=C ratio found in cutin, which is supportive of the presence of ester C=O groups. CHal/C=O value (0.8) of J. coriacea compares with those recorded for Lycopersicon esculentum (0.8; extant) and Macroneuropteris sheuchzeri (0.9; Pennsylvanian), which indicates a similar cross-linking degree of the monomers characterizing the cutin of both extant and fossil taxa.