Fish with human arms!

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So often, there are two stories to be heard when one hears of the latest ‘missing link’ finds: the popular media story and the proper story told in the science journals that rarely gets a mention. This has especially been the case this year with fish-to-frog evolution, with the discoveries of the Tiktaalik fossil and a new species of ‘walking’ shark recently paraded in the media as if they were irrefutable proof of fish-to-frog evolution. Now a new candidate has stepped up to take the spotlight: a magnificently preserved fish fossil called Gogonasus. Gogonasus has received the usual media parade reserved for ‘missing links’, boldly proclaiming that the fins are ‘like human arms’.1 As usual, the original Nature article2 is far more conservative about the claims. So what is the actual story behind this fossil?

Did you ever look at the skeleton of the fish? that might help to see what their are claiming to be human-like.

yeah we definitely evolved from something like that

Everyone remembered hearing about the prehistorical shark found in Japan right?

A fish with human arms really Just kidding but it would be interesting to see.

Got any good just-so stories as to how the intermediates survived or, better yet, had a survival advantage compared to non mutant varieties?

Gogonasus (meaning "snout from Gogo") was a lobe-finned fish known from 3-dimensionally preserved 380 million-year-old fossils found from the Gogo Formation in Western Australia. It lived in the late Devonian period, on what was once a 1400 kilometre coral reef off the Kimberley coast surrounding the north-west of Australia. Its skeleton shows several features that were like those of a four-legged land animal (tetrapod). They included the structure of its middle ear, and its fins show the precursors of the forearm bones, the radius and ulna. Researchers believe it used its forearm-like fins to dart out of the reef to catch prey.

Gogonasus was first described from a single snout (ethmosphenoid) by John Long (1985). On Long's 1986 expedition to Gogo the first relatively complete skull of Gogonasus was found by Chris Nelson and after being prepared solved a scientific controversy by showing that the inner large fangs of the coronoid bones did not insert into the choana of the palate (Long 1988) as had been suggested by Rosen et al (1981) for Eusthenopteron. In 1990 a combined expedition from the Western Australian Museum and the Australian National University yielded another almost complete skull of Gogonasus, this one found by Dr R.E. Barwick. The full description of its cranial anatomy appeared in Long, J. A., Barwick, R. E. & Campbell, K.S.W. (1997), although not all aspects of the skull were clear then even from the 3 specimens. In 2005 Long lead another expedition back to Gogo and on July 11th one of the team members, Dr Tim Senden from the Australian National University, found a very well-preserved skeleton of Gogonasus, containing almost the complete fish down to the tip of the tail. It was Dr Senden's first field trip with the other researchers.

The specimen is now held at Museum Victoria, after nearly 4 months of acetic acid preparation by John Long. The new specimen showed some surprising new data not seen in any of the other specimens. Firstly, there were large spiracular openings on top of the skull, with a distinct down folded cosmine-covered lamina of bone present on the tabular bone. This indicated its spiracles were almost as large as in the elpistostegalian fishes (like Tiktaalik) and early tetrapods (eg Acanthostega). Secondly, after preparation of its pectoral fins, the internal limb skeleton showed closer resemblances to that of the elpistostegalians than to other more generalised tetrapodomorph fishes like Eusthenopteron. For almost 100 years Eusthenopteron had been the well-used role model for demonstrating stages in the evolution of lobe-finned fishes to tetrapods. Gogonasus now replaces Eusthenopteron in being a better preserved representative without any ambiguity in interpreting its anatomy (as had been shown for example by Rosen et al. 1981 when erroneously reconstructing ithe fit of the lower jaws to the palate). Gogonasus is in superficial look similar to the generalised tetrapodomorph fishes like Osteolepis from Scotland, but in its advanced features shows that even primitive-looking cosmine-covered forms evolved significant specializations towards becoming tetrapod-like.

Gogonasus is just one of the almost 45 species of 3-dimensionally preserved fishes from the Gogo Formation deposit. It is the only Devonian site in the world to yield whole complete fishes in perfect uncrushed preservation in some specimens.

Gogo Formation deposit. It is the only Devonian site in the world to yield whole complete fishes in perfect uncrushed preservation in some specimens.