QUANTITATIVE TAPHONOMIC ASSESSMENT OF ANOMALOCARIS FROM MIDDLE CAMBRIAN SHALES OF THE SOUTHWESTERN UNITED STATES

Arguably one of the most intriguing groups of organisms in the history of life, Anomalocaris and the broader great appendage arthropods have recently once again become a hot spot in paleobiological research. From wrongful early classifications resulting from its propensity for disarticulation, to recent discoveries of preserved neurological structure and interpretations of suspension feeding appendage morphologies, anomalocaridids provide exciting targets for taphonomic analysis. Primary preservation of specific Anomalocaris anatomical structures, including mouth structures, appendages, and abdominal sections, results from their recalcitrant composition, while the soft tissues rapidly decayed and contributed to disarticulation. This study comparatively examines preservational features of different disarticulated anatomies, mainly from the middle Cambrian House Range, from specific Lagerstätten in Nevada and Utah, USA. Our samples, from the collections of the Kansas Biodiversity Institute, are largely preserved as carbonaceous compressions, ranging in color from black-to-gray, with some showing rusty iron- oxide surface staining. Taphonomic analyses, including micromorphological and microchemical investigation, were conducted using an FEI Quanta 600F variable-pressure scanning electron microscope. Samples were analyzed in backscatter electron mode for compositional imaging, secondary electron mode for topographic/morphological imaging, and with an integrated energy-dispersive X-ray spectrometer for elemental/mineralogical characterization. A principal components analysis was used to quantitatively analyze these data, with comparisons to known empirical mineral formulas to determine mineralogy. These analyses allow for quantitative taphonomic characterization and comparison between differing Anomalocaris anatomies, possibly illustrating histological underpinnings of preservation.