A molecular signature of chitin in Paleozoic arthropods Structural, molecular and isotopic composition of organic fossils and their relationship to modern counterparts Derek E.G. Briggs, Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520 A molecular signature of chitin in Paleozoic arthropods A synchrotron based Scanning Transmission X-ray Microscope/ microspectrometer (STXM) was used to generate functional group ‘maps’ of modern and fossil (Pennsylvanian, ~310 My) scorpion cuticle. The modern scorpion cuticle is ~25 m thick. The fossil scorpion cuticle is much thinner (~2m) and is only a remnant of the original. The modern cuticle shows variation in the distribution of nitrogen bearing functionality (A). Regions rich in N appear brighter. The outer cuticle (top left) is relatively depleted in N. The N content is higher within the thicker inner cuticle particularly in irregular layers. The modern cuticle also shows variation in the distribution of aliphatic carbon (B). The outer region appears brighter and is enriched. The layers of the inner cuticle enriched in aliphatic carbon are the same as those enriched in nitrogen, revealing a higher protein content. Nitrogen Carbon Outer Modern Inner Fossil Even though it is much thinner and only represents part of the original, the fossil scorpion cuticle retains compositional lamination in both nitrogen and aliphatic carbon content (C, D). X-ray Absorption Near Edge Structure (XANES) spectra revealed a molecular signature of chitin in the fossil scorpion cuticle and also in a Silurian (~417 My) eurypterid (E). E