The teeth of these two species are quite similar in appearance which is complicated by the fact that each species comes in two versions of unlike tooth sets (this also occurs in C. plumbeus). This may be due to sexual dimorphism but I have been unable to confirm this. In both species, with increasing size of the shark, the teeth become much wider and only a little longer.

Carcharhinus obscurus (LeSUEUR, 1818)

Teeth of the dusky shark, Carcharhinus obscurus are the most common find in the Yorktown formation. The teeth come in two versions.

The first version is roughly triangular with fairly straight root edges and a straight or wavy medial cutting edge. The mesial edge is more smoothly curved inward. The lower teeth are massive with the tips of the cusps erect or angled rearward and possess fine serrations.

The second type (possibly female and rarer in the mine) has u-shaped root edges and smoothly, outwardly curving medial cutting edges and smoothly inwardly curving mesial cutting edges. The finely serrated cusps of the lower teeth also smoothly curve mesially.

The serrations (of both types) are typically irregular and coarse. The nutrative groove is often strong with the foramina (small hole in the nutrative groove) located at or above the thickest part of the root.

Fig 2 & 3 -- Carcharhinus obscurus Type 1 and Type 2 upper and lower teeth. Lingual views (left to right): anterio-lateral, lateral & posterior The largest tooth in these images is 27 mm wide and 27 mm slant height

Carcharhinus leucus (VALENCIENNES, 1839)

The bull shark, Carcharhinus leucus, is a far less common find than the dusky shark in the Yorktown formation. (Note: both are also found in Florida, but there, the bull shark is in the majority).

The teeth also come in two versions. The first version is very triangular with curved root edges. The lower teeth are massive with strongly curved roots and erect, angular blades.

The second type (also possibly female) strongly resembles the type 2 dusky teeth. Unlikethe dusky, the serrations are typically more regular and less coarse. The nutrative groove is often weaker and the foramina is located below the thickest part of the root.

Fig. 4 & 5 Carcharhinus leucus Labial (Fig. 4) and lingual (Fig. 5) views of Type 1 (top) and Type 2 (bottom) anterio-laterals, laterals & a lower. In Fig. 5, upper anterio-laterals are on the left and the laterals on the right. The largest tooth in this image is 28 mm wide and 28 mm slant height