Molecular Taphonomy of Plant Organic Skeletons

Abstract

Selective preservation of resistant biomacromolecules, such as cutan in leaf cuticles; lignin in woods, fruit walls and seed coats; sporopollenin in spores and pollen and algaenan in algal cysts, has previously been invoked in survival of these tissues and organs in the fossil record. A growing body of evidence is questioning this paradigm, suggesting that biomacromolecules may provide the structural template for formation of geomacromolecules in fos- sils which form as the result of (i) polymerization of labile constituents (e.g. in situ polymerization of cutin, waxes and internal lipids in cuticles; oxidative polymerization incorporating an aliphatic component into sporopollenin), (ii) loss (e.g. loss of cellulose from lignin–cellulose complexes), and (iii) transformation (e.g. lignin methoxyphenols to phenols). Recommended future research directions include: (a) taphonomic experiments to simulate the molecular alteration sequence in diverse environments, (b) analysis of fossils (time series) from a range of depositional settings, and (c) identifying those modern plant organs that lack an expected fossil record. This will require a combination of microscopical and chemical approaches to monitor alteration and understand specific controls on plant preservation.