Bone and teeth, specialised bio-mineralized connective tissues, are left after the typical decomposition process of any vertebrate organism. Their analysis can reveal insights into an organism's life and retrace the history of the remains after death (also known as taphonomy), which ultimately evolves to destruction or fossilization. Studies on the taphonomy of terrestrial mammalian bio-mineralized tissues have mostly focussed on terrestrial depositional environments. Here, samples submerged in the marine environment are investigated. Five archaeological bones of terrestrial mammalian species (pig and oxen) with historically known post-mortem submersion interval (PMSI) (69–316 years) and recovery sites, were analysed macroscopically, microscopically and by microCT. The aim was to characterize for the first time the alterations produced by marine bioeroding sponges, and to discuss their potential interdisciplinary application, with special focus on forensic investigations. The pig samples showed microanatomical preservation (Oxford Histological Index = 3–5), increased total porosity, the presence of old tissue flakes with sponge spicules and traces of bioerosion, such as papillary holes, canals and chambers with microsculptured walls. The presence of such tissue flakes suggested that, at the time of recovery, they may have been free of sediment and inhabited by live sponges. The shape of one internal chamber was identified as the ichnospecies Entobia convoluta as typically produced by shallow, warm-water Cliothosa spp. Surface analyses for further biological evidence remained inconclusive. The taphonomy of skeletal remains has always been relevant in anthropological, natural and forensic studies. In forensics, the role of taphonomy is to contribute to personal identification, cause of death and post-mortem interval (PMI). This study detected the past colonization of terrestrial mammalian bone by marine bioeroding sponges, and aimed to link the taphonomic findings to natural processes and environments. Bioeroding sponges are for the first time confirmed to colonize terrestrial mammalian bone submerged in marine environments, and to promote diagenesis through bioerosion.