Australia: The Land Where Time Began

A biography of the Australian continent 

Lower Cretaceous Sharks and Bony Fish

The Toolebuc Formation and the Allaru Mudstone both of upper Albian age in the northern section of the Eromanga Basin in central western Queensland, as well as other deposits from the Lower Cretaceous have produced shark and bony fish faunas. Aptian deposits, such as the Bulldog Shale, have produced rare chondrichthyan fossils - sharks, rays and skates, and osteichthyan (bony fish) remains. Edaphodon, the earliest known chimaerid (rat fish) was found in the Bulldog Shale in deposits near Lake Eyre. Opal mines at Coober Pedy and Andamooka have produced isolated bones, mainly vertebrae, of small teleost fish. The Darwin Formation near Darwin, Northern Territory, of upper Aptian age, has produced large vertebrae up to 125 mm in diameter of lamniform sharks, the group including makos, tiger sharks, etc., specimens that are huge when compared to those of white pointers (great white sharks) of the present, suggesting that at more than 6 m long they were probably top predators in the marine environments of the Australian continental margin.

In the Toolebuc Formation and Allaru Mudstone, as well as the Gearle Siltstone, of upper Albian age, from Western Australia, fish assemblages from the Albian have been documented. In the Coorikiana Sandstone, South Australia, there are sporadic finds in the form of isolated teeth, vertebral centra and accumulations of scales from the Albian suggest, according to the authors1, cosmopolitan affinities. The authors3 have listed a number of these taxa:

In the Gearle Siltstone, continental margin sediments, Notorhynchus aptiensis, a hexanchoid (cow shark) was very common; Paraorthacodus, a widespread form that was known from the European Late Cretaceous; Anomotodon or Scapanorhynchus, a mitsukurinid; Cretalamna appendiculata; Carcharias striatula, Paraisurus, Archaeolamna, Leptostyrax, and possibly Cretoxyrhina; Microcorax, Squalicorax primaevus and Pseudocorax australis, of which the commonest genus of shark in Queensland deposits during the Albian was P. australis.

In the Toolebuc Formation tooth plates and fin spines have been found that correspond to at least 1 genus and species of endemic chimaeroid, Ptykoptychion tayyo.  The authors1 suggest it is significant that isolated rostral teeth of Pristiophorus tumidens, a sawshark, representing the oldest known specimen of this widespread taxon as well as the only specimen known from the Cretaceous of the Southern  Hemisphere is present in this formation.

In the Toolebuc Formation bony fish fossils from the Albian are extremely common. Also common are large articulated skeletons, though isolated teeth and bones comprise much of the material from this deposit. Among the described taxa are a number of primitive forms such as Richmondichthys sweeti, a 1.5 m long armoured aspidorhynchid that was a filter feeder entirely lacking teeth and a predatory fish Australopachycormus hurleyi, a swordfish like pachycormid. Among the teleosts present are :

Flindersichthys denmeadi, an elopiform, Cooyoo australis, a predatory ichthyodectid that was large, the skull measuring up to 400 mm, and 'Cladocyclus sweeti';

Pachyrhizodus marathonensis, that was closely related to forms that were well known in the Northern Hemisphere;

Dugaldia emmilta, a small neoteleost.

The authors1 say these fish have important palaeobiogeographical links to 3 other continents, both the Americas and Europe.

Sources & Further reading

  1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.
Author: M. H. Monroe
Last updated  15/12/2011

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