Gladioserratus - Shark

Fossil photo | Wed 14 Dec 2011  

Lower jaw tooth of the extinct broadnose sevengill shark Gladioserratus, found in the lower part of the Gearle Siltstone (laid down 105 million years ago). This shark belongs to a group known as the hexanchids. They differ from other sharks in having six or seven gill slits instead of five and by having a single dorsal fin (most sharks have two). One of the living species, the broadnose sevengill shark Notorynchus cepedianus (see image below) occurs in shallow water whereas the rest spend most of their time in deep cold water.

Adult sevengill sharks (2-3 metres long) are apex predators and use a variety of hunting techniques to capture and subdue their prey. Large and dangerous prey like South African fur seals, twice as heavy as the sevengill, is typically approached by a whole pack of Notorynchus. They subsequently encircle the seal, cutting off its escape route. After an initial attack by one of the sharks the others quickly join in. Lone sevengills have been observed attacking juvenile seals at the surface by using stealth technique, slowly ‘gliding’ towards the seal from below with minimal movement of the tail. Unlike white sharks which begin to include seals and dolphins at a rather large size (around 3 metres), broadnose sevengills begin to include marine mammals in their diet at around 1.5 metres in body length.

Broadnose sevengill shark (Notorynchus cepedianus)
Broadnose sevengill shark (Notorynchus cepedianus), Photo by José María Pérez Nuñez, Image copyright under Creative Commons 2.0.