Identification of shark teeth of the genus Squalus is not easy. Both fossil and extant species are difficult to identify. However, an accurate morphological comparison of the teeth of these sharks may provide useful information for some of them. Therefore, we first attempted to compare the morphology of the aprons, which are considered to be a good representation of tooth characteristics, using a variety of shark teeth of the genus Squalus.

Fig. 1. Measurements of the dental aprons of two extant shark species of the genus Squalus.

Fig. 2. Comparison of the dental apron of sharks of the genus Squalus from two Miocene localities: the Kodera Mountain Formation, Ishikawa Prefecture, Japan, and the Sharkytooth Hill Bone Bed, USA.

Measurements indicated that the fossil teeth of the Sharktooth Hill Bone Bed have wider and larger aprons than those of the two extant species shown in Figure 1. Fossil shark teeth from the Kodera Mountain Formation may have even wider and larger aprons than those of the American Sharktooth Hill fossil teeth.

The results of the measurements carried out in the present study show that the size and shape of the tooth aprons of sharks of the genus Squalus are characterised by continuous variation. In other words, no sharks are considered to have aprons of a unique size and shape.