Gogonasus - artist's impression
Image: Brian Choo
Source: Museum Victoria
New fossil specimen at Museum Victoria may link fish and land animals, rewriting the history of animal evolution.
Gogonasus (meaning "snout from Gogo") was a lobe-finned fish that lived 380 million years ago (the Late Devonian Period), on what was once a great barrier reef surrounding the north-west of Australia.
Initially described from only a snout by John Long in 1985, the new specimen represents a complete fish and was found by a Museum Victoria expedition in July 2005, in a limestone nodule near Fitzroy Crossing known as the Gogo Formation.
Fish fossils preserved there were prepared using weak acetic acid, which dissolves rock without harming the bone material. Four months of delicate preparation was required for the skull and pectoral fin to be revealed in perfect 3-D form.
The new specimen shows us that Gogonasus had large holes on top of the head called spiracles, which were used for taking in air. These structures would eventually evolve into the Eustachian tube or middle ear of higher land vertebrates.
The front fin of Gogonasus shows remarkable similarity with that of all land vertebrates (tetrapods) in having a well-developed humerus, ulna and radius. This feature reveals that such fishes had much more in common with land animals than previously thought.
The specimen was found by Tim Senden of the Australian National University (ANU), who has developed an ultra-fine CT scanner which was used to study the fossil at a level of detail never before seen.
Research on the significance of the new fossil is a joint collaboration between Museum Victoria (John Long), the ANU (Gavin Young, Tim Senden) and Monash University students based at MV (Tim Holland, Erich Fitzgerald), and was published online in Nature magazine on October 18th 2006.
Long, J.A., Young, G.C., Holland, T., Senden, T.J. & Fitzgerald, E.M. 2006. An exceptional Devonian fish from Australia sheds light on tetrapod origins. Nature doi10.1038/nature05243
Long, J.A. 2006. Swimming in Stone- the amazing Gogo fossils of the Kimberley. Fremantle Arts centre Press, 320pp. ISBN1921064331 (out Nov 2006).
Long, J.A. 2004. Gogo Fish! The story of the Western Australian state fossil emblem. W.A., Museum, Perth. 48pp. ISBN 1920843108.