How ancient exoskeletons became preserved in fossils

Science : The exoskeletons of ants, ticks, and other arthropods, both ancient and modern, are made up of proteins, sugars, and calcium carbonate. When an arthropod dies, microbes begin eating the first two components of the shell. The upshot for paleontologists is that little of an ancient arthropod’s exoskeleton survives as a fossil. But some exoskeleton does survive, and now, as Science‘s Sid Perkins reports, we know why. George Cody of the Carnegie Institution of Washington and his collaborators applied x-ray absorption near edge structure (XANES) spectromicroscopy to the fossilized remains of two arthropods, a 310-million-year-old land scorpion and a 417-million-year-old sea scorpion. Comparison with modern scorpions revealed that what remained of the fossilized exoskeletons had been chemically modified, possibly by chemicals from the exoskeleton’s original waxy coating. When the scorpions were alive, the waxy coating prevented their exoskeletons from drying out. When they died, the coating decomposed, releasing chemicals that stabilized the exoskeleton’s proteinsugar complex.