Bone histology in a fossil elephant (Elephas maximus) from Pulau Bangka, Indonesia

Abstract

Analyses of Pleistocene fossil proboscideans have long been used as indirect evidence for climactic and environmental shifts in the Sunda shelf of Southeast Asia. Reconstructing the biological effects of rainforest expansion at the Last Glacial Maximum on elephants can be enhanced by a better understanding of fossil proboscidean palaeobiology. We studied fragmented post-cranial fossil remains of an Asian elephant (Elephas maximus) from Pulau Bangka, an island to the east of Sumatra, hypothesised to be within the Late Pleistocene Sundaland savannah corridor. Bone histology of the humerus, rib, and vertebrae from the Bangka fossil were examined and compared with modern conspecifics to reconstruct remodelling. We measured secondary osteon population density, osteon area, diameter, and infill ratios in Haversian bone. Intra-skeletally, we found that the histology of the largely weight-bearing humerus indicated slower remodelling than that of the ribs and vertebrae, which are less biomechanically constrained. Inter-skeletally, the fossil rib histology showed relatively smaller osteons and Haversian canals when compared to the modern samples. Differences in lifestyles, including range-expansion, may have influenced micro-morphometric differences in elephant rib histology. Our results contribute indirect evidence of the effects of climactic variability in the Sunda palaeoenvironment on Pleistocene fauna.