Dalatias, Rafinesque, 1810

Yun, Chan-gyu, 2021, First Deep-Sea Shark Fossil Teeth From The Miocene Of South Korea, Zoodiversity 55 (3), pp. 225-232 : 228

Dalatias cf. D. licha ( Bonnaterre, 1788)

R e f e r r e d m a t e r i a l. One lower lateral tooth CNUNHM-F392 ( fig. 3 ).

Description: CNUNHM-F392 is a nearly complete lower lateral tooth that is only missing a labial part of a mesial root lobe that is broken off, and an apex of the cusp embed within a matrix. The exposed height of the crown is about 4.06 mm. The cusp is sub-vertical, although the axis is slightly inclined distally. Both cutting edges are serrated, but it is not certain whether the serrations are directed upwards as they are extremely small having about 5–6 serrations per mm in the mesial edge. Small serrations are present on the distal heel as well. The crown width is 6.64 mm at its basis, and the length of the heel is 1.47 mm. The root is high, and both mesial and distal edges are nearly straight. The maximum height of the root is 7.72 mm and the width is 7.13 mm. The part where the “button hole” in dalatiid lower teeth would be is filled with matrix, but it is likely that it is similarly shaped as in other Dalatias teeth as both mesial and distal aprons surrounding it are not different from other examples of this genus (e. g., Cappetta, 2012: Fig. 112 D). Having a relatively low profile of the cusp and a transversely wide, tongue-shaped nature of the mesial apron, it is possible that this tooth comes from a more lateral position teeth within the lower jaw.

Remarks. For the same reason as CNUNHM-F279, CNUNHM-F392 is assignable to Dalatiidae . The specimen probably shares a button-shaped foramen with Dalatias and Isistius but distinguishable from the latter in having a distal heel ( Pollerspöck and Straube, 2018). Therefore, referral to Dalatias is very plausible. However, CNUNHM-F392 differs from lower teeth of both Neogene and modern specimens of Dalatias licha in having minute serrations along the main cusp’s cutting edges. While it is possible that this is merely due to a preservational artifact or an individual variation, the impossibility of removal of the tooth from the matrix makes it impossible to verify this assignment. Thus, a more tentative approach of referring this specimen as Dalatias cf. D. licha is used here.

Figures

Fig. 3. Tooth of Dalatias cf. D. licha, CNUNHM-F392: A — photograph of the specimen; B — enlarged photograph of the labial surface of the tooth. Left scale bar, for A, equals 10 mm. Right scale bar, for B, equals 5 mm.