The cow sharks, Hexanchus (sixgill shark) and Notorynchus (sevengill shark), are some of the more sought after species in the mine, particularly Hexanchus and symphyseal teeth of either species.

Notorynchus (which no longer resides in the Atlantic) is found both in the lower Pungo River and lower Yorktown formations. Hexanchus, which grows much larger, is a rare find in the Yorktown formation. Both have long lineages and differ from most sharks by having lower teeth which are larger than the uppers. Both sharks also demonstrate sexual dimorphism in that the teeth differ in males and females.

Notorynchus primigenius allegedly differs from the modern N. cepedianus (PERON, 1807) by having more erect cusps. However variations in the modern tooth form (and the fossils as illustrated) makes this a somewhat dubious distinction. Thus I believe the fossil species to be the same as the modern one. A potential source of confusion occurs in that the fossil species naming predates the modern species. Illustrated in both lingual and labial views are: an anterior upper tooth (Pungo), a lateral upper tooth (Pungo), a male lower lateral tooth (Yorktown), and an unusually large female lower lateral tooth (Yorktown). The posterior teeth are minute, irregular, and stubby and would be barely recognizable as a tooth. In addition to being smaller, these teeth differ from Hexanchus in having less cusps on the lower teeth (7 vs 8 - 12+) and larger more recurved serrations on the anterior side of the tooth which don't extend as far down along the front of the root.

Fig. 1 Notorynchus cepedianus Top: Upper lateral (side) & anterior (middle), lingual teeth on left. Bottom: Lower lateral female (left) & male (right) lingual above & labial below, female width 33 mm

Also illustrated are lingual views of Notorynchus female (left) and male (right) lower lateral teeth from the same jaw position from the Pungo and Yorktown formatons respectively. Notice the more erect cusplets and greater relative size and separation of the first cusp from the remaining cusps in the male tooth.

Fig. 2 Notorynchus cepedianus Lingual views of similarly positioned lower laterals. Female from Pungo River (left) and male from Yorktown (right). Width of female tooth is 27 mm

The below specimen is a symphyseal Notorynchus tooth from the Pungo River formation. Note, one cusp is missing. Presence or absence of the center cusp is not indicative of genus as this varies by individual. The best method is by size, a Hexanchus symphyseal tooth would typically be quite a bit larger than this one.

Fig. 3 Notorynchus cepedianus Pungo River symphyseal, width 16 mm

Fig. 4 cf Notorynchus cepedianus Pungo River symphyseal, from the collection of B.J. Blake

Fig. 5 cf Notorynchus cepedianus patho symphysio-lateral

Hexanchus griseus (BONNATERRE, 1788)

It has been traditional to ascribe these teeth to H. gigas (SISMONDA, 1857) which is probably synonymous with the modern sixgill shark H. griseus. These are highly prized and rare finds from the Yorktown formation. Unfortunately, along with Notorynchus these are fragile specimens and coupled with their size are consequently often found broken. They display the same sort of sexual dimorphism that Notorynchus does.

Illustrated in the labial and lingual view are two upper lateral teeth and a lower male and lower female lateral tooth.

Hexanchus griseus lateral teeth Fig. 6 labial and Fig. 7. lingual view uppers are on top and lowers on the bottom (in Fig 7, the female lower is on the left and male, the right) Width of the lower lateral female tooth is 40 mm