A rich collection of exceptionally preserved Lower Triassic fossil fish remains obtained during the Polish Spitsbergen Expedition of 2005 includes many isolated teeth believed to belong to a saurichthyid actinopterygian. Stable isotope analysis ( d 13 C and d 18 O) of putative Saurichthys teeth from the Hornsund area (South Spitsbergen) acting as a paleoenvironmental proxy has permitted trophic−level reconstruction and comparison with other Lower Triassic fish teeth from the same location. The broader range of d 13 C values obtained for durophagous teeth of the hybodont selachian, Lissodus , probably reflects its migratory behaviour and perhaps a greater feeding diversity. X−ray microcomputed tomography (XMT), a non−destructive technique, is used for the first time in order to elucidate de − tails of tooth histology, the results of which suggest that the method has considerable potential as a future analytical tool.