Chitin in the fossil record: identification and quantification of D-glucosamine

摘要

Although a labile molecule, cQitinls resistant to decay when complexedwith protein. Currently, qualitative evidence for the preservation of chitin rests upon characteristic marker compounds derived through pyrolysiS'-gas chromatography- mass spectrometry (Py-GC-MS) of fossil arthropod cuticles, supported bya non-specific carbohydrate assay. However, unambiguous confirmation of the survival of chitin polymer requires detection ofits hydrolysate monomer, D-glucosamine. We have now developed a GC-MSselected ion monitoring (SIM) method for the identification and quantification Of'D- glucosamine in fossil materials. Fossils of various ages and depositional settings were investigated and the results compared with those obtained by the Py--GC-MS approach. Specimens from the Rancho La Brea Tar Pits (USA, Pleistocene), showed the greatest degree of preservation: -10% (w/w), while fossil insects from Willershausen (Germany, Pliocene) and St Bauzile (France, Miocene) showed chitin to be present in -5% (w/w). Fossils from the Oligocene at Enspel, Ger- many, revealed that more than 0.5% is preserved for 25 million years. The GC-MS-SIM technique confirms the survival of chitin in the fossil record through the explicit identification of the polysaccharide monomer, and supports earlier Py-GC- MS and colorimetric analyses. The presence of other amino sugars of either exogenous (microbial) or diagenetic origin in more ancient specimens was also readily revealed using the GC-MS-SIM approach. This study illustrates the value ofusing a high-specificity quantitative 'wet' chemical approach in combination with Py--GC-M!> to further advance the inves,,; tigation of chitin in the fossil record.