EXPERIMENTAL DEGRADATION OF CHICKEN FEATHER PROTEINS IN RESIN

Proteins are a valuable tool for studying the phylogeny and evolution of living and recent fossil organisms, providing information that is not available from morphology alone. In recent years there has been significant interest among palaeontologists in extending the range of preserved proteins deeper into geologic time. Fossils in amber are of particular interest in the search for preserved proteins: bioinclusions in amber often have exceptionally preserved soft tissues; amber dehydrates all inclusions which should inhibit hydrolysis, one of the major pathways of protein degradation; and the amber fossil record extends into the Triassic.

We have used taphonomic experiments to investigate the rate of protein degradation in amber. Experimental feathers in amber were prepared by embedding fragments of freshly plucked Gallus gallus domesticus (domestic chicken) feathers in freshly extruded Wollemia nobilis resin. Feather fossils are common in amber, and W. nobilis is an Araucariacean, a family of trees known to produce extensive amber, copal, and resin deposits from the Cretaceous to the recent. Each experiment was artificially aged at 110°C or 140°C. Protein degradation was assessed after 1, 2 and 3 weeks in each treatment group using amino acid racemization (AAR); the higher the ratio of right to left handed amino acids (D/L), the more the proteins have broken down. Our experiments indicated very slow rates of protein degradation in resin; even after three weeks at 140°C, there was minimal racemization, with D/L<0.25 for all amino acids. In contrast, all previous experiments reported in the literature, on different types of samples, showed complete racemization in most amino acids by this point. Therefore, fossils in amber are very likely to provide the most geologically ancient preserved proteins in the fossil record.