Bone microanatomy and weight-bearing adaptations in the giant proboscidean Deinotherium giganteum (Kaup, 1829)

Bone anatomy reflects the mechanical and functional constraints to which the skeleton is subjected. In graviportal taxa, the primary constraint is gravity, requiring specific adaptations in bone structure. Proboscideans, including modern elephants and their fossil relatives, illustrate these adaptations, notably through a columnar posture that optimizes load transmission. While adaptations of external bone morphology have been described within this order, variations in bone microanatomy have rarely been studied in fossil proboscideans. In this study, we analyze for the first time the microanatomy of a Deinotherium giganteum (Kaup, 1829) femur, a fossil species from the Deinotheriidae Bonaparte, 1845 family, based on a fractured specimen preserved at the Hungarian Natural History Museum. We compare these observations with those of a Mammuthus sp. femur to assess similarities and differences in weight-bearing adaptations across different proboscidean families. Our results reveal shared characteristics between the two taxa, including a thick-walled diaphysis, a medullary cavity largely filled with trabecular tissue, and highly anisotropic trabeculae aligned with axial loading, features also observed in modern elephants. However, D. giganteum exhibits a more pronounced hourglass-shaped cortical distribution and relatively greater cortical thickness than Mammuthus sp., suggesting differences in load distribution or distinct weight-bearing adaptation strategies between these two taxa.