Exceptional preservation of large fossil vertebrates in a volcanic setting (Camp dels Ninots, Spain)

The taphonomic study of two complete and anatomically connected individuals of Tapirus arvernensis from the Pliocene site of Camp dels Ninots (Caldes de Malavella, Spain) strengthens the attribution to a konservat-Lagerstatte deposit. The macroscopic analysis showed the absence of weathering, predation marks, and scarce superficial modification. Different surface colourations have been observed, highlighting white alteration. A selection of samples was analysed through ESEM-EDX, XRD and FTIR. Results suggest preservation of histological features and absence of microtunneling associated with biotic digestion of bioapatite. Specific white alteration of bone surfaces are attributed to a slightly different phase of the bone apatite, with higher crystallinity index and heavier loss in biogenic carbonates. Together with the presence of silicon-rich crusts and infillings that cover bone surfaces, it is now suspected that some interference of the volcanic activity that occurred in the past could have been responsible for an optimal preservation of the osteological material. A slow remineralisation could have been caused by hydrothermal activity still active in the area that caused the absence of bacterial activity in a lacustrine context and left the specimens undisturbed. These results could proportionate new data to understand fossil diagenetic mechanisms that could potentially allow exceptional preservation in maar contexts.