Australia: The Land Where Time Began

A biography of the Australian continent 

Canowindra Fossil Site See The Age of Fishes Museum

This New South Wales site, about 4 hrs drive west of Sydney, is of similar age to that of Mt Howitt. The preservation of the fossils is exquisite. It is believed to have been the site of fish kill from the Devonian, the fish appear to have been trapped in a pool or lake as it dried up, probably during a prolonged dry period, about 360 million years ago, the remains being covered by sediment when the rains returned. 3700 fish were recovered from this site, most of which are complete.

Placoderms

There are high concentrations of placoderms packed together on sandstone slabs. Among the placoderms common at the site are the antiarchs Bothriolepis, about 50 cm long, and Remigolepis, about 35 cm long.

Another fish found in the Canowindra deposit was the arthrodire Groenlandaspis, about 50 cm long. It has been found around the world, the first specimen being found in Greenland. The body shield of Groenlandaspis rose steeply to form a dorsal ridge that had a fin-like appearance, and the pectoral fins were protected by bony projections from the side of the shield.

Crossopterygians

Canowindra, about 50 cm long, had a broad, flat head that was similar in appearance to that of a reptile, and had 2 rows of teeth. Its body was long and sleek, and covered with bone reinforced scales. It was the first sarcopterygian to be described from Australia. 

Another fish, the euarthrodire Groenlandaspis, has also been found at the Canowindra site. Many of the 50 specimens of Groenlandaspis, many of which are complete and even articulated.

Sarcopterygians

Among the fish at Canowindra were 3 new species, Mandageria, about 1.6 m, Gooloogongia, about 90 cm, and Cabonnichthys, about 70 cm, that look similar to modern pike. A common feature of all 3 is a large, flat head with pointed teeth lining the jaws, and fangs. They had long cylindrical bodies with the fins mostly at the rear.

Mandageria is thought to have probably been a top predator, at least at Canowindra, and because of its shape, being similar to a pike, led to the suggestion that it may have been an ambush predator, as is the pike. About 12 specimens have been found at Canowindra.

Cabonnichthys had 2 rows of teeth, the outer row being small teeth and the inner row of large fangs. The result was a strong interlocking bite.

Gooloogongia is a rhizodont sarcopterygian, the main distinguishing feature of which is strong rooted teeth. The Canowindra deposit contains the most complete fossils of rhizodonts in the world.

Dipnoans

Another new species of fish from Canowindra is the 22 cm dipnoan Soederberghia. It had a long, wedge-shaped skull, the end of which was a broad, square, flattened snout. The body was laterally compressed, being much higher than wide. The lobed shaped pectoral fins were long and the other fins occurred mainly at the rear of the body. The shape of the snout suggests it may have been used to sift through the sediment for creatures such as small invertebrates.

It was first described from East Greenland deposits of a similar age, also being found in America and another Australian site at Jemalong Gap near Forbes, New South Wales, 90 km west of Canowindra. The skull and much of the body of a specimen has been found at Canowindra.

Devonian distribution

When the Canowindra fish were alive during the Late Devonian Australia was part of Gondwana, a northern peninsula of Antarctica and was situated in the tropics on the northern side of the Equator. The North American and Greenland sites where Soederberghia was found was in the same latitude as Australia, but on the opposite side on the Equator in the Southern Hemisphere. The fish from all the sites are believed to have lived in the similar climatic conditions, and the same climate probably existed across the world from east to west. The landmasses the sites were situated on were separated by as little as 100 km along the same latitude making it easy to swim between the landmasses.

Sources & Further reading

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

Links

  1. The Age of Fishes Museum, Canowindra, New South Wales

 

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Last Updated 12/01/2009

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading