Lipid Incorporation During Experimental Decay of Arthropods - Biopolymers: A Molecular Paleontology Approach - page 115

Ancient sedimentary organic matter is formed by diagenetic alteration of
precursor biological material yielding a non-hydrolysable, organic solvent-insolu-
ble macromolecule called kerogen (Tissot and Welte 1984 ). Kerogen formation is
fundamental to the formation of fossil fuels and to the preservation of organic fos-
sils. The formation of kerogen depends on the nature of the biological input, the
environment of deposition and the diagenetic pathway (de Leeuw 2007 ; de Leeuw
et al. 2006 ). Kerogens that serve as a source of petroleum products following cata-
genesis have a high hydrogen content because of signifi cant aliphatic components
in the macromolecule (e.g., Type I/II). Recent research revealed that labile compo-
nents such as lipids become incorporated in situ to generate an aliphatic component,
a process demonstrated in a range of fossils of diverse starting compositions includ-
ing chitin, protein, lignin, polysaccharides, cutin and cutan (for review see Gupta
et al. 2007e ; de Leeuw 2007 ). Oxidative crosslinking may play an important role
during early diagenesis where molecular oxygen reacts with unsaturated lipids to
form a macromolecular n -alkyl component as demonstrated in fossil algae
(Versteegh et al. 2004 ) and invertebrates (Gupta et al. 2008a ).
The focus on seeking the oldest examples of original chemical constituents such
as chitin and protein in fossils (e.g., Stankiewicz et al. 1997 ; Gupta et al. 2007c ), has
meant that less attention has been devoted to determining the rate at which the trans-
formation to an aliphatic composition takes place. Future studies should focus on
archaeological and late Cenozoic remains, investigating progressively older mate-
rial in order to detect the onset of lipid incorporation and presence of an aliphatic
component in the geopolymer. Aliphatics are present in Hymenaea leaves from
~20,000 year old fossil resin from Kenya, for example, although they are absent
from insect remains from the same source (Stankiewicz et al. 1998b ). The evidence
presented here demonstrates that the formation an aliphatic macromolecule through
the incorporation of lipids into decaying tissues does not require elevated tempera-
tures and pressures. This result lends important experimental confi rmation of the
concept of in situ lipid incorporation and geopolymer formation as a mechanism for
generating the signifi cant aliphatic content ubiquitous in fossil organic matter.
Furthermore it shows that this process can start at a very early stage, during the
decay of the organism.
References
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