Calculation of density and biomechanical properties of coalified carboniferous pteridosperms

ZODROW, ERWIN L.; D`ANGELO J A

Simposio; XVII Simposio Argentino de Paleobotánica y Palinología; 2018

We present a new methodology for obtaining density values of pinnules and rachides. In turn,densiVes values are used to esVmate some of their biomechanical properVes i.e., tensile modulus ofelasVcity (TME), tensile strength (TS), and flexural sVffness (FS), which cannot be determinedexperimentally. Samples analyzed include the largest known compression-preserved frond segmentsof Alethopteris ambigua (45-cm long) and Neuropteris ovata (65-cm long) (Medullosales,Pennsylvanian, Sydney, Canada). Our methodology includes the following steps: (i) Pinnules andrachides are analyzed by Fourier transform infrared spectroscopy, and data are evaluated by PCA(principal component analysis); (ii) PCA-loading plots indicate which combinaVons of chemical groupsare associated with which pinnule or rachis; (iii) Different chemical-group combinaVons found in (ii)allow proposing standards (i.e., molecules having parVcular chemical structures), which areassociated with specific pinnules and rachides; (iv) Using a group-contribuVon method, density valuesare calculated for standards proposed in (iii). Thus, standards and their corresponding density valuesare associated with pinnules and rachides; (v) Finally, using well-known mathemaVcal models linkingdensity to biomechanical properVes in living plants we obtain TME, TS, and FS for A. ambigua and N.ovata specimens. These biomechanical properVes indicate that, for example, ulVmate rachides ofboth taxa were relaVvely bri)le (not flexible). This suggests an adapVve ?self-pruning? strategy ofboth taxa in strong winds during Pennsylvanian tropical storms. This biomechanical behavior possiblyhelped to reduce mechanical failure of bigger axial structures, peVoles, or even the main trunk.