Australia: The Land Where Time Began

A biography of the Australian continent 

Late Cretaceous Sharks and Fish

In the Murchison River area, Carnarvon Basin of Western Australia much work has been carried out, especially on the middle Cenomanian deposits of the Gearle Siltstone and the Alinga Formation. Among the sharks found in the Gearle Siltstone was Dwardius woodwardi, a species that is also known from chalk deposits in England, Cardarbiadon ricki. Vertebrae of Cardarbiadon have been measures up to 90 mm in diameter. This vertebra size ratio is comparable to that of the white pointer (great white shark) that grows up to 15 m in length. In the Alinga Formation the shark fauna is comprised of species that are widespread and long-range types, most notable of which are Cretalamna appendiculata and Cretoxyrhina mantelli. There are also other genera such as Anomotodon and Johnlongia, taxa with good records in North America and Europe.

Compared with the shark fauna of the these deposits those in the Molecap Greensand and Gingin deposits from the Turonian-Coniacian are not well documented, though there are isolated teeth and large vertebral centra that have been attributed to indeterminate lamniforms. The authors3 have listed the principal finds in the Gearle Siltstone and the Alinga Formation:

Notorhynchus aptiensis a hexanchoid (cow shark);

Centrophoroides and Protosqualus, squalids (dog fish);

Anomotodon, mitsukurinid-like, commonly found in North America and Europe;

Squatina, a long-ranging genus;

Protolamna, Cretalamna (C. appendiculata and an endemic species C. gonsoni), lamnids, the most common of the shark genera in the Molecap Greensand is C. gonsoni.

Two sharks reported rom the Gingin Chalk are Squalicorax, an anacoracid, and Paraorthacodus, a palaeospinacid. The authors3 suggest the chimaerid (rat fish) remains may include a species of Ischyodus that is globally distributed. A mandibular toothplate attributable to Edaphodon, a chimaerid, has been found in deposits from the Early Cretaceous in the Lake Eyre region, South Australia. In the Campanian-Masstrichtian of Australia fossils of sharks are virtually unknown.

Enchorhinus eryensis teeth have been reported in rocks dredged from the Great Australian Bight and deposits of the Miria Formation at Cardabia Station in Western Australia. In the Miria Formation in the Giralia Ranges a large vertebra of an anacoracid shark have been collected that has tentatively assigned to the genus Squalicorax. Throughout much of the Lower Cretaceous this genus had an almost worldwide distribution, though by the end of the Mesozoic it was extinct.

In the Molecap Greensand bony fish are rare and none have been found in the Miria Formation or the Korojon Calcarenite. Protosphyraena, a cosmopolitan swordfish-like pachycormid  from the Cretaceous has been found in the Gingin Chalk. Of the few isolated teleost teeth that have been found none have been formally identified or described.

Fish have also been found in the Winton Formation, that is non-marine, that included many lungfish and fragmentary teleosts. The authors3 suggest the isolated lungfish fossils can be assigned to Metaceratodus, one of the largest lungfish from Australia that had toothplates up to 60 mm in diameter. There are 2 known species of Metaceratodus, M. wollastoni, also found in the Lightning Ridge deposits and in the Otway Ranges from the Lower Cretaceous. M. ellioti is a smaller fish that has been found in the Winton Formation, Queensland and Lake Eyre in South Australia





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                                                                                           Author: M.H.Monroe  Email:     Sources & Further reading