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| Gogonasus | |
|---|---|
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| Skull ofG. andrewsae,National Museum of Natural History | |
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| Life restoration ofG. andrewsae | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sarcopterygii |
| Clade: | Tetrapodomorpha |
| Order: | †Osteolepiformes |
| Family: | †Osteolepidae |
| Genus: | †Gogonasus Long, 1985 |
| Type species | |
| †Gogonasus andrewsae Long, 1985 | |
Gogonasus (meaning "snout from Gogo") was alobe-finned fish known from three-dimensionally preserved 380-million-year-old fossils found from theGogo Formation inWestern Australia. It lived in the LateDevonian period, on what was once a 1,400-kilometre-long (870 mi; 760 nmi)coral reef off theKimberley coast surrounding north-western Australia.Gogonasus was a small fish reaching 30 to 40 centimetres (12 to 16 in) in length.[1]
Its skeleton shows several features that were like those of a four-legged land animal (tetrapod). They included the structure of itsmiddle ear, and its fins show the precursors of theforearm bones, theradius andulna. Researchers believe it used its forearm-like fins to dart out of the reef to catchprey.
Gogonasus was first described from a single snout (ethmosphenoid) byJohn A. Long (1985). On Long's 1967 expedition to Gogo the first relatively complete skull ofGogonasus was found by Chris Nelson and after being prepared by SheilaMahala Andrews solved a scientific controversy by showing that the inner largefangs of thecoronoid bones did not insert into thechoana of thepalate (Long 1988) as had been suggested by Rosenet al. (1981) forEusthenopteron. In 1990 a combined expedition from theWestern Australian Museum and theAustralian National University yielded another almost complete skull ofGogonasus, 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 three specimens. In 2005 Long led another expedition back to Gogo and on July 11 one of the team members, Dr Tim Senden from the Australian National University, found a very well-preserved skeleton ofGogonasus, containing almost the complete fish down to the tip of thetail. It was Dr Senden's first field trip with the other researchers.
The specimen (NMV P221807) is now held atMuseums Victoria, after nearly four months ofacetic 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-foldedcosmine-coveredlamina of bone present on thetabular bone. This indicated itsspiracles were almost as large as in theelpistostegalian fishes (likeTiktaalik) and early tetrapods (e.g.Acanthostega). Secondly, after preparation of itspectoral fins, the internal limb skeleton showed closer resemblances to that of the elpistostegalians than to other more generalisedtetrapodomorph fishes likeEusthenopteron. For almost 100 yearsEusthenopteron had been the well-used role model for demonstrating stages in the evolution oflobe-finned fishes totetrapods.Gogonasus now replacesEusthenopteron in being a better preserved representative without any ambiguity in interpreting its anatomy (as had been shown for example by Rosenet al. 1981 when erroneously reconstructing the fit of the lower jaws to the palate). Superficially,Gogonasus appears similar to the generalised tetrapodomorph fishes likeOsteolepis 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 over 45 species of three-dimensionally preserved fishes from the Gogo Formation deposit. It is the onlyDevonian site in the world to yield whole complete fishes in perfect uncrushed preservation in some specimens.
Other fish found in fossils from the Devonian period:
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