Gogonasus

Taxobox
name = "Gogonasus"
fossil_range = Late Devonian

---

image_width = 250px
image_caption = life restoration of "Gogonasus andrewsae"
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
classis = Sarcopterygii
infraclassis = Tetrapodomorpha
superordo = ?Osteolepidida
ordo = ?Osteolepiformes
familia = ?Osteolepidae
genus = "Gogonasus"
genus_authority = Long, 1985
species = "G. andrewsae"
binomial = "Gogonasus andrewsae"
binomial_authority = Long, 1985

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.

ee also

Other fish found in fossils from the Devonian period:
*"Tiktaalik"
*"Eusthenopteron"
*"Panderichthys"
*"Coelacanthimorpha"
*"Materpiscis"

References

* Long, J. A., 1985, "A new osteolepidid fish from the Upper Devonian Gogo Formation of Western Australia", Recs. W. A. Mus. 12, 361–377.
* Long, J. A. 1988, Late Devonian fishes from Gogo, Western Australia. Nat. Geog Research & Exploration 4: 436-450.
* Long, J. A. et al., 1997, "Osteology and functional morphology of the osteolepiform fish Gogonasus Long, 1985, from the Upper Devonian Gogo Formation, Western Australia", Recs. W. A. Mus. Suppl. 57, 1–89
* Long, J. A. et al., 2006, "An exceptional Devonian fish from Australia sheds light on tetrapod origins", Nature 444, 199-202
* Long, J. A. 2006. "Swimming in Stone -the amazing Gogo fossils of the Kimberley" Fremantle Arts Centre Press, Fremantle. 320pp. ISBN 1-921064-33-1
* Rosen, D. E., Forey, P.L., Gardiner, B.G. & Patterson, C. 1981, Lungfishes, tetrapods, paleontology and plesiomorphy. Bull. Am. musm. Nat. Hist. 167 (4): 159-276.

External links

* [http://www.museum.vic.gov.au/hottopics/show.asp?ID=672 Ancient Gogonasus advances evolution] , Museum Victoria.
* [http://wwwrsphysse.anu.edu.au/~tjs110/Gogonasus/ Photographs and x-ray micro-tomography animation of "Gogonasus"] from ANU
* [http://scienceblogs.com/pharyngula/2006/10/gogonasus_andrewsae.php "Gogonasus andrewsae"] by PZ Myers
* [http://news.nationalgeographic.com/news/2006/10/061018-fossil-fish.html Ancient Fish Fossil May Rewrite Story of Animal Evolution] (National Geographic)
* [http://www.livescience.com/animalworld/061018_leggy_fish.html Livescience.com: "Discovery Points to Our Fishy Heritage." (Accessed 10/21/06)]
* [http://www.foxnews.com/story/0,2933,222152,00.html?sPage=fnc.science/evolution Fox News: Primitive Fish Skeleton May Link Land, Sea]
* [http://www.abc.net.au/rn/inconversation/stories/2007/1876587.htm#transcript Interview with Dr John Long, curator at the Museum of Victoria]