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

Although a labile molecule, chitin is resistant to decay when complexed with 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 by a non-specific carbohydrate assay. However, unambiguous confirmation of the survival of chitin polymer requires detection of its hydrolysate monomer, D-glucosamine. We have now developed a GC-MS selected 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: similar to 10% (w/w), while fossil insects from Willershausen (Germany, Pliocene) and St Bauzile (France, Miocene) showed chitin to be present in similar to5% (w/w). Fossils from the Oligocene at Enspel, Germany, 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-GCMS 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 of using a high-specificity quantitative 'wet' chemical approach in combination with Py-GC-MS to further advance the investigation of chitin in the fossil record. (C) 2001 Elsevier Science Ltd. All rights reserved.