“Petrified” freshwater crab
This is a “petrified” freshwater crab (Potamos potamois, Olivier, 1804).
This freshwater crab belongs to the genus Potamon (Savigny, 1816), probably to the species potamios (Olivier, 1804). It dates from the Middle Pleistocene (≈ 450,000 years ago), which is consistent with measurements made using thermoluminescence. (Pasini & Garassimo, 2011).
It comes from Denizli Travertine Quarry (Denizli Basin), South-western Turkey.
The genus still exists today, notably the (endangered) species Potamon fluviatile (Herbst, 1785), whose habitat consists of calm waterways in the north-northeast Mediterranean.
The mineralisation of the exoskeleton of this crab, in its burrow, was formed by coating, resulting from a strong emergence of hot geothermal waters which, in this region, emerge at ≈ 35°to 56 °C and are very rich in hydrogen carbonate and calcium precipitation in the form of calcium carbonates. Here, it is calcite (CaCO3), identified by micro-Raman spectroscopy.
It is not exactly a fossil, as the fossilisation process involves the replacement of tissues and skeletons (or exoskeletons) by the surrounding mineral substances. This is not the case here, as this exoskeleton (who disappeared) is only coated with calcium carbonate.