Australia: The Land Where Time Began

A biography of the Australian continent 

Sarcopterygians

This group of fish is comprised of the lobe-finned fish and dipnoans (lung fish), with 2 known living forms, coelacanths and lung fish. They have modified cosmoid scales, thinner than the true cosmoid scales of the earlier fish.

Sarcopterygians had paired lobed fins joined to the skeleton by a single bone, that led to the evolution of legs in the first amphibians, and the had 2 dorsal fins with separate bases, the actinopterygians (ray-finned fish) had a single dorsal fin. The Sarcopterygii have traditionally been grouped in with the Osteichthyes, but some taxonomists believe they should be assigned to their own superclass, based on the differences from other osteichthyans - fin structure, respiratory structure, and circulatory structure.

The earliest known sarcopterygians, from the Upper Silurian, resembled acanthodians. They were most closely related to the Actinopterygians. It is believed they evolved in the ocean and moved to freshwater in the Devonian, possibly to escape from the predatory placoderms that were dominant in the seas during the Early to Middle Devonian.

Sources & Further reading

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

Links

1. The Age of Fishes Museum, Canowindra, New South Wales