I have been re-examining the fossil teeth of carcharhinids from the Oligocene
Yamaga formation, Ashiya group in Kitakyusyu city. The fossil teeth from
this formation are relatively well-preserved, but they often bear cracks
caused by crustal movements such as earthquakes. The fossil containing
matrix is very solid, therefore isolating the root in the teeth without
distinctive damages is almost not possible, and the fossil with the damaged
root makes it difficult to identify with accuracy. This time, I examined
a total of 306 samples. As a result, 172 teeth (54.9%) among them were
assigned to carcharhinids. The most abundant species among them were Isogomphodon (18.3%), Negaprion (17.0%), and an unidentified species (15.4%). The unidentified species
is very close to Isogomphodon in its form, but its cutting-edge is incomplete while Isogomphodon bears complete cutting-edges. The teeth of Negaprion have very weak serrations in the heals, and were assigned to N. acutidens rather than N. brebirostris. |