Australia: The Land Where Time Began

A biography of the Australian continent 

The hexanchiform sharks (7-gilled sharks) first appeared in the Mesozoic. A Middle Devonian form, Mcmurdodus, is thought to possibly belong to this group. Some living primitive forms of this Order are the cowsharks, Hexanchus, Heptranchias and Notorhynchus, having a single dorsal fin and 6-7 gill slit pairs. They have characteristic teeth comprised of a broad root with many flat cusps. The dentitions of the upper and lower jaws show marked differences. They usually feed on fish and are often found in deep water. Teeth of this group first appear in the fossil record in Jurassic.

Sources & Further reading

1. John A Long The Rise of Fishes - 500 Million years of Evolution, University of New South Wales Press, 1995

Chondrichthyans