3D IMAGING OF PYRITIZED SOFT TISSUES IN PALEOZOIC KONSERVAT-LAGERSTÄTTEN

Pyritization of soft tissue is rare, but important because the high density contrast between pyritized fossils and their matrix allows x-radiography to be used to characterize morphologic features in minute detail. X-radiography is particularly useful when soft-tissues are difficult to expose using mechanical preparation techniques. For example, conventional and stereo x-radiography of the Upper Ordovician Frankfort Formation of New York (i.e., Beecher’s Trilobite Bed) and the Lower Devonian Hunsrück Slate of Budenbach, Germany has proved instrumental in assessing the paleobiology and evolution of early soft-bodied megascopic invertebrates. Another pyritic deposit in which x-radiography may prove useful is the Middle Devonian Silica Shale of Sylvania, Ohio.

To augment previous work in these deposits, we have begun using computed tomographic x-radiography to assess the paleobiology and taphonomy of their faunas, as well as to construct 3D models of some of the smaller and lesser-known soft-bodied organisms. In Beecher’s Trilobite Bed and the Hunsrück Slate, soft tissues of trilobites, graptolites, and nautiloids are visible in 3D using CT, even in extremely small specimens where pyritization of soft-tissues has not been well documented. For example, meraspid and protaspid Triarthrus eatoni from Beecher’s Trilobite Bed appear to be less compacted than holaspids analyzed in previous studies, and meraspids have clearly visible antennae, gut, and three pairs of biramous cephalic appendages. In biomineralized taxa where morphologic information may be obscured because appendages are superimposed on one another, CT has allowed us to distinguish and/or digitally remove individual limbs to examine underlying features, such as the arms of the Hunsrück Slate crinoid Taxocrinus stuertzi and the asteroid Urasterella asperula. Internal features of biomineralized taxa are also visible using CT, and have allowed us to construct models of the coiled lophophore support structures inside pyritized steinkerns of the Silica Shale brachiopod Paraspirifer bownockeri. Together, this type of CT-based 3D information offers the potential to test hypotheses about the ontogeny and morphology of pyritized biotas, without painstaking mechanical preparation of specimens.