Australia: The Land Where Time Began

A biography of the Australian continent 

Gogonasus

Study of this complete skeleton found there were large spiracles on top of the skull with a down-folded cosmine-covered bone lamina on the tabular bone. It's spiracles were almost as large as those of elpistostegalian fish, such as Tiktaalik, and early tetrapods, such as Acanthostega. The structure of the internal limb skeleton shows closer similarity to elpistostegalians than to the more generalised tetrapodomorph fish such as Eusthenopteron. Gogonasus is now used to demonstrate the evolutionary stages leading from lobe-finned fish to tetrapods because it is better preserved and so more detail is known about its structure, and interpretation is not required,  than the previously used Eusthenopteron.

The superficial appearance of Gogonasus is similar to that of generalised tetrapodomorph fish such as Osteolepis from Scotland. Its advanced features show that the primitive-looking cosmine-covered forms had evolved significant specialisations in the direction of the tetrapods.

Sources & Further reading

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