NEW INFORMATION ABOUT THE INTERNAL ANATOMY AND TAPHONOMIC HISTORY OF TRILOBITES REVEALED THROUGH CT SCANNING

X-ray computed tomography (CT or XCT) scans were taken of eight species of trilobites hypothesized to have internal remains replicated and preserved through early diagenetic processes. Specimens range in age from Cambrian Epoch 3 (~505 Ma) to Late Ordovician (~445 Ma). XCT scans reveal early mineralization lining the digestive systems. Studied forms show either a non-bifurcate digestive system architecture (interpreted as primitive) or a bifurcate architecture (interpreted as derived). Taxa showing a non-bifurcate architecture are Elrathia kingii, Modocia typicalis, Modocia laevinucha, Labiostria westropi, Alokistocare idahoensis, Olenoides nevadensis, Hemirhodon amplipyge, (all Cambrian), and Flexicalymene retrorsa (Ordovician). Isoteloides flexus (Ordovician) shows a bifurcate digestive system architecture. Fossilization of the digestive tract resulted from early mineralization around decaying soft parts. Early diagenetic mineralization must have occurred quickly after death of the animal, possibly beginning within days to a few weeks. It must have begun before significant decay of the animal had occurred. The mineralization that occurred around the digestive tract contrasted with the fossilization processes that affected the calcite-reinforced exoskeleton. CT imaging also reveals that preserved guts can be used as geopetal indicators. Unfilled or later-stage mineralization within fluid-filled internal cavities, recognizable in scans, indicates stratigraphic-top direction.