MATERIALS AND METHODS

Youngina Material

All specimens of Youngina are known from the Permian Tropidostoma-Dicynodon assemblage zones of the Karoo Basin of South Africa. Two of the earliest described specimens are housed in the USA, the holotype of Y. capensis, AMNH 5561 (Broom 1914, Broom 1915), and the holotype of Youngoides romeri, UC 1528 (Olsen 1936). These specimens were made available on loan to one of the authors (O'Keefe).

HRXCT Scanning and Visualization

Preliminary CT scanning of both specimens in the medical CT scanner at SUNY Stoneybrook revealed that only the holotype (AMNH 5561) showed enough differentiation between bone and matrix to justify the expense of HRXCT scanning. The holotype was therefore scanned at Penn State University's Center for Quantitative Imaging on the X-TEK X-ray subsystem (X-ray energy set at 180 kV, 0.500 mA) with a source object distance of 137.771 mm. Within a 43 mm field of reconstruction, 1353, 0.04777 mm thick slices were generated. For each slice, 2400 views were taken with three samples per view. Raw 1024 by 1024 pixel, 16-bit TIFF files were pre-processed using Strip2raw (Nathan Jeffery, University of Liverpool, UK and then imported into Amira v.4.0 (Visage Imaging, Inc., San Diego) to render 3D images of our HRXCT data and allow segmentation of individual elements as 3D models.