DNA from excrements can be amplified by means of the polymerase chain reaction. However, this has not been possible with ancient feces. Cross-links between reducing sugars and amino groups were shown to exist in a Pleistocene coprolite from Gypsum Cave, Nevada. A chemical agent, N-phenacylthiazolium bromide, that cleaves such cross-links made it possible to amplify DNA sequences. Analyses of these DNA sequences showed that the coprolite is derived from an extinct sloth, presumably the Shasta ground sloth Nothrotheriops shastensis. Plant DNA sequences from seven groups of plants were identified in the coprolite. The plant assemblage that formed part of the sloth's diet exists today at elevations about 800 meters higher than the cave.

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Chitin is present in fossil insects from the Oligocene (24.7 million years ago) lacustrine shales of Enspel, Germany. This result, which was obtained by analytical pyrolysis, extends by nearly 25 million years the length of time that chemically detectable remains of this biomolecule are known to survive. The embedding sediment is dominated by diatoms, which reflect high productivity in the paleolake. The primary control on the preservation of chitin is thus not time; it may persist in older sediments where suitable paleoenvironmental conditions prevailed.

Flash pyrolysis/gas chromatography (py/GC) and py/GC/mass spectrometry (MS) have been utilized to characterize the cuticles of invertebrates chemically. Pyrolysis products have been identified and assigned to specific cuticular components. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones are proposed as characteristic pyrolysis markers for chitin. Pyrolysis products displaying ions of m/z 70,154,168,194 are thought to derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. These products, constituting specific pyrolysis markers for invertebrate cuticles, may reflect the amino acid composition of their constituent structural proteins. The source of the various pyrolysis products of proteins has been verified by pyrolysis of reference proteins, peptides and amino acid m ' - Chitin [poly-( 1-.4)-P~-2-acetarnido-2deoxyglucopyra-nose] (Fig. 1) is one of the most important biopolymers in the biosphere, occurring in many organisms.' In arthropods, chitin is one of the major constituents of the cuticle,' where it occurs in intimate association with proteins, connected through covalent cross-links involving catechol-amine and histidine/aspartic moieties.' Studies of chitin have utilized a range of analytical method^^-^ to resolve questions relating to its chemical composition and production techn~logy.~ Studies of the chemical structure of arthropod cuticles have focused mainly on insects, and have been advanced by the use of solid-state 13C and/or I5N nuclear magnetic resonance (NMR)?' Information from these studies has included the determination of the general chemical structure of the cuticle, recognition of chitin and other moieties, and investigation of the chemical changes involved in the sclerotization of exoskeletons.' Pyrolysis/gas chromatography (py/GC) and py/GC/mass spectrometry (py/GC/MS) are widely used analytical techniques for the studies of insoluble, polymeric organic materials?-" These techniques allow very rapid screening of complex materials and require only submilligram sample sizes. The facility to accommodate minute samples is critical for the study of fossil materials. The sensitivity of the MS ensures that even traces of the polymers in organic residues can be detected qualitatively.' Chitin and proteinaceous materials have been studied by means of analytical pyrolysis to assess their chemical composition and degradation products."-'7 Nonetheless, use of these techniques in studies of arthropod cuticles, which are highly intractable to Author for correspondence. conventional chemical methds, has been limited. They have, however, been analysed using enzymatic methods." One area in which py/GC and py/GC/MS are proving to be the most appropriate analytical techniques is in the study of the fossilization of animal cuticles.''* Preliminary results indicated that chitin, although relatively resistant to degradation," was not detectabl...