Lipid Incorporation During Experimental Decay of Arthropods - Biopolymers: A Molecular Paleontology Approach - page 106

Chapter 6
Lipid Incorporation During Experimental
Decay of Arthropods
Abstract Laboratory decay experiments were carried out on shrimps, scorpions
and cockroaches to monitor changes in the chitin-protein of the arthropod cuticle
and associated lipids. The cockroach and scorpion exoskeleton remained largely
unaltered morphologically, but the shrimp experienced rapid decomposition within
a month that progressed through the 44 week duration of the experiment as revealed
by electron microscopy. Mass spectrometry and 13 C NMR spectroscopy revealed the
association of an n -alkyl component with labile lipids, such as fatty acids with up to
24 carbon atoms, which were incorporated into the decaying macromolecule. The
scorpion and cockroach cuticle did not reveal the incorporation of additional lipids
indicating that decay is important in initiating in situ lipid association. This experi-
ment provides evidence that lipids can become associated with carbohydrate and
proteinaceous macromolecules during the very early stages of decay representing
the fi rst stage of the transformation process that contributes to the aliphatic rich
composition ubiquitous in organic fossils and in kerogens.
Keywords Taphonomy • Kerogen • Fossil • Pyrolysis • Spectroscopy • Gas
chromatograph- mass spectrometry • Chitin • Lipids • Melanoidin
Introduction
Research on the organically preserved cuticles of fossil arthropods has shown that
only younger examples retain traces of the chitin-protein complex that is the pri-
mary component of the cuticle of living arthropods (Stankiewicz et al. 1997 ; Gupta
et al. 2007a ; de Leeuw 2007 ). Cuticles of plant and animal origin are transformed
during diagenesis to geopolymers with a signifi cant long chain aliphatic compo-
nent (Briggs 1999 ; Stankiewicz et al. 2000 ). Such a transformation is common to a
range of other organic remains (de Leeuw et al. 2006 ) with different starting com-
positions, including graptolites (Briggs et al. 1995 ; Gupta et al. 2006a ) and leaves
(Mösle et al. 1998 ; Gupta et al. 2006b , 2007b ), and the analysis of such fossils is