Marine bryozoan colonization of terrestrial biomineralized tissues: Taphonomic insights and forensic implications

The taphonomy and diagenesis of bone and teeth recovered from any environments provide crucial information for forensic sciences and investigations. This leads to the estimation of the postmortem interval (PMI) and the postmortem submersion interval (PMSI) of the organism/s. Aquatic taxa can induce macroscopic and microscopic alterations in biomineralized tissues (e.g., grooves) or can colonize them by attachment (e.g., Bryozoa). Bryozoa are tiny invertebrates that form colonies in freshwater and saltwater. They can survive for years as suspension feeders in all climates. Most marine Bryozoa species have a biomineralized exoskeleton that can be preserved after their death. This research analyzes eight fragments of archeological elephant ivory with a known PMSI of 314 years, which were inhabited by three distinct bryozoan colonies. The variations in the preservation of the bryozoan exoskeletons and the overgrowth of different marine taxa reveal that one colony (lichenoporid cyclostomatid) was alive at the time of the ivory collection from the submerged archeological site while the two other colonies (cheilostomatid) had previously died at different times. The primary objective of this observation is to contribute to the understanding of the taphonomy of terrestrial mammalian biomineralized tissues recovered in marine environments. Additionally, the study discusses the potential forensic implications of this association, such as the evidence of marine submersion and the PMSI. A secondary objective is to present the Bryozoa colonies within a distinctive depositional context, considering that many bryozoan species of the Western Australian coast remain undescribed. The complexity of the Bryozoa ecobiology is also highlighted, with the need of further research (e.g., minimum time for colonization). Finally, this study highlights the urgency of multidisciplinary collaboration to advance aquatic forensic capabilities.