micro-CT scanning data of Byttneria fossil flowers

The amber specimens were prepared and photographed following the conventional approach. The two specimens were prepared in China and Germany independently. The specimen of Byttneria zhangpuensis sp. nov. (PB21529) was first examined and photographed using a Zeiss Stereo Discovery V16 (Carl Zeiss, Oberkochen, Germany) microscope system with z-axis stacking, a Leica M205A stereomicroscope (Leica, Wetzlar, Germany), and a Leica DMC5400 digital camera system with z-axis stacking using the Leica Application Suite X software at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. In order to investigate the internal structure and anatomy of the fossil flowers, we also scanned the specimen with micro-CT (μCT). Micro-CT scanning was performed using a Zeiss Xradia 520 Versa 3D X-ray microscope, with a 4 × optical magnification lens, exposure time 3.5 s, and 2401 projections at a voltage of 40 kv. The micro-CT data was processed using VGStudio MAX 3.0.0 software to obtain successive virtual sections and surface renderings.Deep fractures partially reached the specimen inclusion PB21530 and hindered in-depth light-microscopic examinations. The specimen was thus embedded in epoxy resin (EpoTek 301-2) to stabilize the amber piece and make the inclusions more visible. The embedded fossil was then ground and polished using a LaboPol-25 machine (Struers, Sarasota, Florida, USA) and wet silicon polishing paper with progressively fine grit sizes (250 to 4000 nm, Struers). This fossil was then studied under a Carl Zeiss AxioScope A1 compound microscope (Carl Zeiss, Oberkochen, Germany), using incident and transmitted light simultaneously and photographed with a Canon EOS 80D digital camera (Canon, Tokyo, Japan) mounted on the microscope. We also used synchrotron-radiation-based X-ray micro-computed tomography (SRμCT) to scan the specimen in order to examine its internal structure and anatomy. Synchrotron tomography was performed at the beamline P05 of the storage ring PETRA III (Deutsches Elektronen-Synchrotron, DESY, Hamburg, Germany) operated by Helmholtz-Zentrum Hereon. Beeswax was used to mount the amber specimens on sample tubes. An attenuation contrast setup was used. The specimen was scanned using a commercial CMOS camera system with an effective pixel size of 0.45 μm, a photon energy of 18 keV, and a sample detector distance of 100 mm. For the tomographic scan, 4001 projections were recorded at equal intervals between 0 and π. The tomographic reconstruction was carried out using a transport of intensity phase retrieval approach a filtered back projection having some edge enhancement. The Astra Toolbox and Matlab (Math-Works) were integrated into a custom reconstruction pipeline. During processing, raw projections were binned twice, giving the reconstructed volume an effective voxel size of 0.91 μm. ImageJ 1.52 (Wayne Rasband, National Institutes of Health, Bethesda, Maryland, USA) was used to reduce the size of the generated tomographic images from 32-bit floating point data to 16-bit. The synchrotron data were processed using VGStudio MAX 3.4 (Volume Graphics, Heidelberg, Germany) to obtain successive virtual sections and surface renderings.