(a) SEM–BSE image acquired near the periosteal area in the artiodactyl bone cross section. Bright areas are rich in heavier elements compared with the darker ones. The arrow indicates the extensive microbial tunneling that appears in the form of spherical nodules. The inset denotes part of the area where SEM–EDX maps were recorded. (b) SEM–BSE image and corresponding SEM–EDX maps (bottom) recorded at approximately 0.6 mm from the periosteum. Notation: FeOx, Fe (hydroxy)oxides; Sd, siderite (FeCO3); CaP, apatite; MCO3, carbonate mineral.