Geology Reference
In-Depth Information
Chapter 8
Transformation of Arthropod Biopolymers
in High P-T Conditions
Abstract
Modern arthropod cuticles consist of chitin fi bres in a protein matrix,
but fossil arthropods, particularly those earlier than Tertiary, yield an aliphatic
composition. This apparent contradiction is addressed in this chapter. Modern
cockroach, scorpion and shrimp cuticle were subjected to artifi cial heating (maturation)
techniques (350 °C/700 Bars/24 h) following various chemical treatments, and ana-
lysing them with pyrolysis-gas chromatography-mass spectrometry. Artifi cially
matured untreated cuticle yielded moieties related to phenols and alkylated substitu-
ents, pyridines, pyrroles and possibly indenes (derived from chitin). Amides, C
16
and C
18
fatty acids and alkane/alk1-1ene homologues ranging from C
10
to C
19
were
also present, the last indicating the presence of an aliphatic polymer, as often
encountered in fossil arthropods. Cuticles matured after lipid extraction and hydro-
lysis did not show the presence of these alkane/alk-1-ene homologues providing
direct experimental evidence that lipids incorporated from the cuticle were the
source of the aliphatic polymer.
Keywords
Arthropod • Lipids • Experimental maturation • Confi ned pyrolysis
• Taphonomy • Fossilisation
Introduction
Arthropod cuticles consist of chitin fi bres embedded in a protein matrix, cross-linked
by catechol, aspartate and histidyl moieties (Schaefer et al.
1987
). Calcifi cation, in
the form of calcium carbonate, further strengthens the cuticle of many crustaceans,
and that of the extinct trilobites; such biomineralised skeletons dominate the marine
fossil record of arthropods. The fossil record of many arthropods, however, particu-
larly in non-marine settings, relies on organic matter preservation, because they lack
a biomineralized exoskeleton. Fossil eurypterids, scorpions and insects, for example,
are abundant as cuticular remains (see Briggs
1999
for review).
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