The organic preservation of fossil arthropods: an experimental study

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 degrees 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.

Experimental maturation of feathers: implications for reconstructions of fossil feather colour

“…The extent to which melanosome geometry is altered varies under different temperature regimes: diagenetic contraction is greater at higher temperature. This may reflect dehydration during condensation/polymerization reactions [12]. Combining such experimental data with information on the burial history of feather-bearing biotas will allow the extent of diagenetic alteration of melanosomes to be predicted; a similar approach has been used in investigations of structural colour in fossil insects [14].…”

“…Artificial maturation techniques can simulate the chemical and morphological effects of burial on integumentary tissues [12,13], including how colourgenerating ultrastructures are altered [14]; elevated pressures and temperatures in experiments accelerate geochemical reactions that occur at lower pressures and temperatures over longer geological timescales [15] (see the electronic supplementary material). We employed high pressure-high temperature autoclave experiments to test, for the first time, the effect of burial on feather ultrastructure and to identify constraints on melanosome-based reconstructions of fossil feather colour.…”

Phylogenetic investigation of the aliphatic, non-hydrolyzable biopolymer algaenan, with a focus on green algae

“…Considering analytical difficulties, the limited diagnostic features of algaenan, the known taphonomic origin of some aliphatic signatures, and limited distribution of algaenan production in modern organisms, algaenan should be interpreted with great caution as a geomacromolecule and a biomarker. It now seems clear that plant and animal fossils, which had living counterparts devoid of algaenan, can have chemical compositions with all the known attributes of an algaenan (Gupta et al, 2007a;Gupta et al, 2006a;Gupta et al, 2006b;Gupta et al, 2007c).…”

Determination of the molecular signature of fossil conifers by experimental palaeochemotaxonomy – Part 1: The Araucariaceae family

“…1), we investigated the palaeochemotaxonomy of several extant species of the Araucariaceae (Table 1) using an experimental method based on artificial maturation by confined pyrolysis (Hautevelle et al, 2006b). This procedure allows simulation of the conversion of biomolecules into their corresponding diagenetic geomolecules (Stankiewicz et al, 2000;Gupta et al, 2006Gupta et al, , 2007. Aims of this study are (1) to determine the common palaeochemotaxonomic (diagenetic) signatures of all extant Araucariaceae species, (2) to evaluate the inter-and intra-generic differences within the family, (3) to highlight the molecular characteristics which should allow their distinction from other conifer families in ancient sediment samples.…”