Preliminary microfocus X-ray computed tomography survey of echinoid fossil microstructure

Microfocus X-ray computed tomography (μCT), a high resolution variant of medical CT, was used to non-invasively examine Jurassic echinoid fossils with spine, demipyramid and test plate fragments serving to assess the extent to which the microstructure remained unaffected by diagenesis. The sizes of the calcite-crystal stereom remains dictated the resolution that could be obtained. The smaller diameter spines were imaged with 9 × 9 × c. 25 μm voxels; the larger demipyramids and test plate fragments were imaged with 13 × 13 μm and 17 × 17 μm voxels, respectively, in the plane of reconstruction and with a proportionally larger slice thickness. The stereom structure was not seen in the μCT slices of the fossils. This is not surprising because, for the ossicles studied, the stereom pore dimensions are, for the most part, smaller than the resolution of the μCT system. Tide marks and other low absorption features were found in the spines and appear to be related to diagenetic changes. What appear to be cleavage cracks were observed in the demipyramid and some of the pores for tube feet could be seen in the test fragment.