SRµCT dataset for the paper "Extending the fossil record of late Oligocene non-biting midges (Chironomidae, Diptera) of New Zealand"

Two  Chironomid specimens preserved in close proximity in nearly opaque amber could not be prepared separately and studied by light microscopy. These specimens (No. OU47580, No. OU47581) were scanned on the Imaging Beamline P05 (Lytaev et al., 2014) operated by the Helmholtz-Zentrum Hereon at the PETRA III storage ring (Deutsches Elektronen Synchrotron - DESY, Hamburg, Germany), using a photon energy of 18 keV and a sample-to-detector distance of 100 mm. Projections were recorded with a custom 20 MP CMOS imaging system with an effective pixel size of 1.28 µm (Lytaev et al., 2014). For each tomographic scan, 3601 projections were recorded at equal intervals between 0 and π. Reconstruction was carried out by applying a transport of intensity phase retrieval approach and using the filtered back projection algorithm (FBP). This workflow was carried out in a custom reconstruction pipeline using Matlab (Math-Works) and the Astra Toolbox (Moosmann et al., 2014; van Aarle et al., 2015, 2016). Raw projections were binned twice for further processing, resulting in an effective pixel size of the reconstructed volume (voxel) of 2.56 µm. Scanned volumes were reconstructed using Drishti ver. 2.6.6 (Limaye, 2012). To decrease the demands for computer memory, we converted all stacks into 8-bit tiffs, downscaled all tiffs by 50% and subsequently cropped the empty space around the amber piece using Fiji ‘scale’ and ‘crop’ functions (Schindelin et al., 2012). Volumes were rendered in Drishti ver. 2.6.6 (Limaye, 2012).