Histology of a Woolly Mammoth (Mammuthus primigenius) Preserved in Permafrost, Yamal Peninsula, Northwest Siberia.

In 2007, the baby woolly mammoth (Mammuthus primigenius) named Lyuba was found frozen in the Siberian tundra permafrost along the Yuribey River. She was proclaimed the best-preserved mammoth discovery. As part of the endoscopic examination of Lyuba, tissue samples of hair, muscle, and internal organs were taken. The sectioned biopsies were stained using standard and special histological stains. In general, the microscopic preservation of the tissue was good although no clearly identifiable cell nuclei were found by standard staining methods. Only a few cell nuclei could be identified in some samples when fluorescence stained with DAPI. The best-preserved structures were collagen fibers and muscle tissue, which gave some structural resemblance to the organs. In the hairs, evidence of pigmentation, a scaly surface, diagonal intra-hair structures, and a medulla were seen. Fat droplets could be identified with Sudan Red in the subcutaneous fat sample and in several organs. Bacteria were seen on the lumen side of the small intestine and caecum, and in the liver and lung tissue. In addition, fungi and pollen were seen in the lung sample. In the wall of the caecum and small intestine, blood vessels and nerves were visualized. Iron was identified in the vivianite sample. Some biopsies compared well structurally with the African elephant tissue sections. The histological findings support the theory that Lyuba drowned in muddy water. The microscopic tissue preservation and cell nuclei destruction indicate that Lyuba's body underwent at least one freeze-thaw cycle.