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The Organic Preservation of Fossil Arthropods: An Experimental Study

Neal S. Gupta, R. Michels, Derek E. G. Briggs, Richard P. Evershed and Richard D. Pancost
Proceedings: Biological Sciences
Vol. 273, No. 1602 (Nov. 7, 2006), pp. 2777-2783
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/25223676
Page Count: 7
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The Organic Preservation of Fossil Arthropods: An Experimental Study
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Abstract

Modern arthropod cuticles consist of chitin fibres in a protein matrix, but those of fossil arthropods with an organic exoskeleton, particularly older than Tertiary, contain a dominant aliphatic component. This apparent contradiction was examined by subjecting modern cockroach, scorpion and shrimp cuticle to artificial maturation (350 °C/700 bars/24 h) following various chemical treatments, and analysing the products with pyrolysis—gas chromatography/mass spectrometry (Py—GC/MS). Analysis of artificially matured untreated cuticle yielded moieties related to phenols and alkylated substituents, pyridines, pyrroles and possibly indenes (derived from chitin). n-Alkyl amides, C₁₆ and C₁₈ fatty acids and alkane/alk-1-ene homologues ranging from C₉ to C₁₉ were also generated, the last indicating the presence of an n-alkyl component, similar in composition to that encountered in fossil arthropods. Similar pyrolysates were obtained from matured pure C₁₆ and C₁₈ fatty acids. Py—GC/MS of cuticles matured after lipid extraction and hydrolysis did not yield any aliphatic polymer. This provides direct experimental evidence that lipids incorporated from the cuticle were the source of aliphatic polymer. This process of in situ polymerization appears to account for most of the fossil record of terrestrial arthropods as well as marine arthropods that lacked a biomineralized exoskeleton.

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