APPLICATIONS OF MACRO CT SCANNING TO THE STUDY OF THE FOSSILS OF THE MAZON CREEK LAGERSTӓTTE

The most obvious problem associated with investigating the form and function of fossils preserved within concretions – 3D morphology that is not revealed on a single plane of splitting – can be addressed by using x-ray tomography (CT scanning) on specimens from some Lagerstӓtten. However, even though exceptionally preserved fossils, such as those from Mazon Creek, reveal morphological information that is otherwise unavailable, their composition may prevent them being clearly visible in a CT scan. Nonetheless, CT scanning can address the two main difficulties involved in studying Mazon Creek fossils: (1) identifying which concretions contain fossils, and (2) determining the best way to access them. Commonly, even though the CT scan does not show a clear, recognizable fossil, it reveals indications that one is present: clusters of spots or lines of higher or lower density than the concretion matrix, or slight irregularities along cracks. These concretions are good candidates to be opened as the fossils cannot be studied from the CT scan alone. A scan will also show internal cracks, which must extend almost to the edge of the concretion to facilitate opening. Otherwise freeze-thawing is necessary to expand the cracks. Where no cracks are present, they are unlikely to develop even through extensive freeze thawing. In such cases the best option may be to cut the concretion open, and serially grind the specimen to reconstruct it. Only in rare cases can the fossil be studied from a CT scan alone.