Unexpected Exoskeleton Remnants Found in Paleozoic Fossils
ScienceDaily (Feb. 8, 2011) — Surprising new research shows that, contrary to conventional belief, remains of chitin-protein complex -- structural materials containing protein and polysaccharide -- are present in abundance in fossils of arthropods from the Paleozoic era. Previously the oldest molecular signature of chitin-protein complex was discovered in 25-million-year-old Cenozoic fossils and remnants of structural protein have also been discovered in 80 million-year-old Mesozoic fossils.
A big surprise is revealed in this soft x-ray absorption image of exoskeleton from a 310-million-year-old scorpion fossil. The brighter areas map the abundance of nitrogen from chitin, which scientists previously believed couldn't endure in extremely old fossils. For scale, the black bar is one-millionth of a meter. (Image courtesy of Carnegie Institution)
Carnegie's George Cody and an international team of scientists discovered relicts of protein-chitin complex in fossils of arthropods from the Paleozoic era. Their findings, published online by Geology, could have major implications for our understanding of the organic fossil record.
Among other common features, arthropods have exoskeletons, or cuticles. The outer portions of these cuticles are made up of a composite of chitin fibers, which are embedded in a matrix of protein. It is well known that chitin and structural protein are easily degraded by microorganisms and it has long been believed that chitin and structural proteins would not be present in fossils of moderate age, let alone in fossils dating back to the early Paleozoic.
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Molecular signature of chitin-protein complex in Paleozoic arthropods
George D. Cody1, Neal S. Gupta1,4, Derek E.G. Briggs2, A.L.D. Kilcoyne3, Roger E. Summons4, Fabien Kenig5, Roy E. Plotnick5 and Andrew C. Scott6
-Author Affiliations
1 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, D.C. 20015, USA
2 Department of Geology and Geophysics, and Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520, USA
3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
4 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
5 University of Illinois at Chicago, Earth and Environmental Sciences, 845 W. Taylor Street, Chicago, Illinois 60607, USA
6 Department of Geology, Royal Holloway University of London, Egham, TW20 0EX Surrey, UK
Abstract
The conventional geochemical view holds that the chitin and structural protein are not preserved in ancient fossils because they are readily degradable through microbial chitinolysis and proteolysis. Here we show a molecular signature of a relict chitin-protein complex preserved in a Pennsylvanian (310 Ma) scorpion cuticle and a Silurian (417 Ma) eurypterid cuticle via analysis with carbon, nitrogen, and oxygen X-ray absorption near edge structure (XANES) spectromicroscopy. High-resolution X-ray microscopy reveals the complex laminar variation in major biomolecule concentration across modern cuticle; XANES spectra highlight the presence of the characteristic functional groups of the chitin-protein complex. Modification of this complex is evident via changes in organic functional groups. Both fossil cuticles contain considerable aliphatic carbon relative to modern cuticle. However, the concentration of vestigial chitin-protein complex is high, 59% and 53% in the fossil scorpion and eurypterid, respectively. Preservation of a high-nitrogen-content chitin-protein residue in organic arthropod cuticle likely depends on condensation of cuticle-derived fatty acids onto a structurally modified chitin-protein molecular scaffold, thus preserving the remnant chitin-protein complex and cuticle from degradation by microorganisms.
Received 6 August 2010.
Revision received 8 October 2010.
Accepted 10 October 2010.
© Geological Society of America
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