DIETARY PREFERENCES OF THE CAMBRIAN TRILOBITE ELRATHIA KINGII: INFERENCES FROM FOSSILIZED DIGESTIVE TRACTS

Specimens of the common trilobite Elrathia kingii from the Wheeler Formation (Cambrian Series 3) of western Utah were studied for their digestive tract contents using standard microscopic, computed tomographic (CT) imaging, and microtomographic (micro-CT) imaging techniques. Specimens showing fossilized alimentary tracts are complete dorsal exoskeletons retaining the librigenae, preserved in cone-in-cone calcite concretions. Examined specimens have collapsed glabellas that approximate the margins of the stomach cavity. Remains of the digestive system are outlined by a thin crust of pyrite, perhaps reflecting early mineralization of a biofilm associated with decay early in the taphonomic process. Similar pyritic crusts have been observed on the hypostome and near the exoskeletal margin. A circular stomach is located in the anterior part of the glabella, and it is followed by a thin, slightly tapering tube that extends the length of the axis. Neither sediment fill nor macerated sclerites have been found in the gut of E. kingii, which tends to rule out the possibility that this trilobite was either a sediment deposit-feeder or a sclerite-ingesting durophagous carnivore. Instead, the presence of an open, pyrite-lined gut suggests a fluid-filled alimentary tract at the time of death, and implies a carnivorous feeding strategy involving separation of the skeletal parts of prey prior to ingestion.