Sweet or bitter? Preliminary data on the biomechanics, physiology, and possible nutritional quality of Cretaceous gymnosperms leaves (Patagonia, Argentina)

This study provides the first data on the relationship between chemical composition and biomechanical/physiological characteristics of foliar gymnosperm compressions from the Lower Cretaceous of Santa Cruz, Argentina. Studied taxa include: Squamastrobus tigrensis, Pseudoctenis ornata, Ginkgoites tigrensis, Ruflorinia orlandoi, and Ptilophyllum micropapillosum. The properties determined include: density, tensile strength (resistance to fracture), tensile modulus of elasticity (stiffness), and leaf mass per area (metabolic cost of tissue construction). They are calculated using a 3D-multivariate model based on data obtained by Fourier transform infrared (FTIR) spectroscopy and trait relationships linking density and the properties mentioned above. Samples have a predominantly aromatic chemical composition with variable carbonyl contents. The chemical groups detected are associated with diagenetically-resistant molecules, possibly including lignins, phenylpropanoids, tannins, and resin-like compounds. The results indicate that these plant taxa may have allocated variable amounts of resources (metabolic costs) for the development of aromatic, biomechanically resistant, and relatively long-lived foliar tissues. The determined chemical, biomechanical, and physiological properties of these leaves suggest their potential as a food source for herbivores. Thus, S. tigrensis leaves might have been unpleasantly astringent, difficult to eat and digest due to their hard tissues, and possibly even hazardous. Conversely, the leaves of G. tigrensis, P. ornata, R. orlandoi, and P. micropapillosum may have been easy to eat due to their softer tissues, offering food of intermediate-high nutritional value. The use of FTIR spectroscopy proves useful to perform detailed and realistic studies on the biomechanics, physiology, and autecology of extinct plants.