Australia: The Land Where Time Began

A biography of the Australian continent 

Xenacanth Sharks

Freshwater sharks very common in the fossil record from the Late Devonian to the Late Jurassic that grew up to 2 m. There is some recent evidence that they may have been euryhaline, so not restricted to freshwater. They had characteristic teeth which had 2 main cusps and a bone button on the root called a lingual torus, having had 2 pointed, elongate lateral cusps with a smaller single median cusp between them. The dorsal fin ran from the head to the tail.

They are well known as complete fossils from the Permian-Triassic of western Europe. A large, serrated defensive spine protruded from their neck, the tail was straight, unlike the heterocercal condition of most sharks. They lived mostly in freshwater, apparently moving up river systems from the sea, as their teeth are also found in marine deposits. An almost complete fossil was found Somersby fish site, near Gosford, NSW.

Sources & Further reading

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