3D VISUALIZATION AND ANALYSIS OF CT IMAGING IN TWO MAMMOTH CALVES

X-ray computed tomography and desktop visualization software provide new modes for studying the anatomy and diagenesis of two female mammoth neonates, Lyuba and Khroma. Lyuba was 30–35 days old at death, about 42 Ka BP. Khroma was about 55 days old at death, and an AMS assay on bone collagen returned an “infinite” result, implying a geological age >45 Ka BP. Partial macro-CT scans were conducted on both mammoths in medical scanners. A full-body scan of Lyuba was conducted in an industrial CT facility and analyzed in Amira 5.4.1. Scans of each mammoth revealed sediment in the trachea and proximal parts of the lungs. Micro-CT imaging of a tissue sample from Lyuba’s lung provided sufficient spatial resolution to allow discrimination and 3D tracing of sediment within surrounding tissue, yielding a 3D model that showed the sediment was confined to the bronchi. This supports suffocation as the probable cause of death. Image segmentation and radio-density thresholding tools were used on micro-CT scans of excised teeth to create surface meshes from which we generated rapid prototypes to use for comparative studies. This was done because the complex structure of the teeth precluded use of traditional molding and casting techniques. Macro-CT scans show authigenic vivianite (hydrated iron phosphate) nodules in Lyuba but not in Khroma. These nodules are concentrated within diaphyses of long bones; larger vivianite accumulations exist on the cranium. The location of vivianite suggests it formed from bone-derived phosphate and hemoglobin-derived iron in the lactic-acid preservational environment produced by bacteria that colonized Lyuba postmortem. Macro-CT documents each mammoth’s skeletogenesis by revealing centers of ossification within bones. Neither mammoth’s skeleton is completely mineralized. This is especially clear in the feet, where cartilaginous precursors to the endochondral bones are preserved. Comparison of 3D models of Khroma’s and Lyuba’s ribs with a texture-mapped model (generated in 3DSOM) of a small rib from an archeological site, Swan Point, in Alaska confirm the Swan Point rib as mammoth. CT analysis of Lyuba and Khroma thus provides a comparative framework that helps to clarify the taphonomy of Swan Point and the nature of human-mammoth interactions in the Alaskan Pleistocene.