The study was focussed on the bones of the head and shoulder skeleton. The studied bones were taken mainly from the viscerocranium and the pectoral girdle. Some highly identifiable bones of the neurocranium (frontale, parasphenoid, vomer, basioccipitale, supraoccipitale) were included too. In addition the pubic plate (pelvis), which is often not situated near the head, and the otoliths were examined. Furthermore the complete set of bones of the head and shoulder girdle (often including some vertebrae) from each species was stored as reference collection.

From each single bone several photos serving as the basis for the bone picture database (Fig. 1) were taken with a digital camera (Ricoh Caplio R3). For the identification key only the biggest and most distinguishable bones were taken into account (Fig. 2).