First record of a highly chemically resistant macropolymer in cuticles of Dicroidium and Johnstonia: a secret arma plantarum against massive extinctions?

D`ANGELO, J A; ZODROW, E L

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

The high resistance to harsh chemical conditions and the refractory nature of cuticles of Johnstonia coriacea and Dicroidium odontopteroides (Corystospermaceae) are recorded for the first time. Additionally, a highly aliphatic, oxidation-resistant, cutin-like macropolymer obtained from the cuticle of J. coriacea is reported. Specimens of Upper Triassic strata (Cacheuta, Argentina) are preserved as (i) fossilized cuticles and (ii) coalified compressions. Changes in functional groups and microscopic structure of cuticle and cutin-like macropolymer as a function of Schulze?s oxidation conditions were monitored via semi-quantitative Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy, and optical microscopy. Specimens of J. coriacea preserved as fossilizedcuticles (i.e., having a certain degree of natural oxidation) were subjected to an unprecedentedoxidation time of 60 days. FTIR monitoring showed the following changes in functional groups with increasing oxidation time: a) considerable decrease of aliphatic groups, with increasing values of CH2/CH3 (i.e., longer and more branched aliphatic side chains), b) increase of C=O compounds and c) disappearance of aromatic groups. Morphological changes were minimal after the 60-day oxidation period. Schulze?s oxidation of coalified compressions, using standard procedure (» 25o C) and hot maceration (» 500o C) yielded similar chemical and morphological results to those described above for fossilized cuticles. Results indicate that highly aliphatic geomacropolymers composing the cuticle of both D. odontopteroides and J. coriacea are extraordinarily resistant to high temperatures and harsh oxidative conditions. It is suggested that this geomacropolymer is likely related to the resistant biomacropolymer making up the cuticle of the once living plants. If confirmed, the high resistance of the ancient biopolymer could be associated with a physiological adaptation tosurviving extreme conditions (e.g., hot and dry environments) as those proposed for Late Triassic times in southern Gondwana.