Inferring bone attribution to species through micro-Computed Tomography: A comparison of third metapodials from Homo sapiens and Ursus americanus

Gross similarities between human hand/foot bones and bear paws have been well-documented. Macroscopic skeletal analyses provide insight into species origin when whole bones are recovered but are frequently rendered inapplicable when bones are fragmented. In these scenarios, histological techniques are often applied; though specific research focusing on the quantification of bear bone microstructure remains scarce. We hypothesized that 3D analysis of bear cortical bone microarchitecture provides a more representative and accurate means to infer bone attribution to species from fragmented metapodials. Methods included visualizing and quantifying bone microstructural parameters using micro-Computed Tomography (µCT). Third metacarpals and metatarsals from mature black bears and humans were assessed using 3D analyses. Micro-CT experiments were carried out using a laboratory X-ray system at The University of Akron. Projections were reconstructed and cylindrical Volumes of Interest (VOIs) were identified within each bone sample. Variables measured within the VOIs included: total volume (TV), total canal volume (Ca.V), canal number (Ca.N), average canal diameter (Ca.Dm), and cortical porosity (Ca.V/TV). Between-species t-tests revealed that both Ca.N and Ca.Dm significantly differed between human and bear metapodials. Qualitative features including osteon banding and resorption bays were more prevalent in bear metapodials. The 3D data for this study were obtained non-destructively and reveal the usefulness of laboratory µCT as a diverse and novel tool for the anthropologist. Results demonstrated differences between the human and black bear third metapodials, supporting the hypothesis that a microstructural comparison is necessary for fragmentary bone identification of human and bear metapodials.