How UV light photography can be of help to palaeontologists?

The analysis of fossil specimens under ultraviolet (UV) light represents a powerful tool in palaeontology. It has been frequently applied in this field only in the last twenty years, although it was discovered at the beginning of the 20^th Century. Up to now this technique has been applied mainly on mollusc shells, but the number of studies dealing with other taxa, like vertebrate specimens, is increasing. Despite this, the analysis of fossil specimens under UV light represents a technique still not fully comprehended; the knowledge of the best procedure of sample preparation and photography still needs to be clarified and new data are required to better understand the real potential of this method. Here, we have tested different preparation (bleached vs not bleached specimens) and photographic techniques to define a protocol for UV analysis of fossil specimens and have explored its main applications analysing specimens from different stratigraphic contexts (from the Permian to the Holocene, from Oman to Italy), having different biominerals (calcite, aragonite, bioapatite and silicified and phosphatized specimens) and belonging to invertebrate and vertebrate taxa (bivalves, gastropods, brachiopods, fish, crustacean and reptile); also, we use two different wavelengths: the commonly used 365 nm, and the 440 nm, a “borderline wavelength” here adopted for the first time. Our results indicate that bleach treatment is not recommended for calcite-shelled brachiopods, whereas is suggested for aragonite-shelled molluscs. We show that UV photography enhances morphological characters and colour patterns and allows to distinguish soft-bodied fossils from the matrix, having important implications in several palaeontological fields and no limitations for its application in invertebrate or vertebrate specimens. Also, the use of UV light provides an inexpensive method to detect man-made interventions in fossil specimens and thus fake fossils. However, the nature of the biomineral and shell microstructures cause different UV responses, whereas the stratigraphic context affects specimen preservation influencing pigment preservation.