Australia: The Land Where Time Began

A biography of the Australian continent 

Triassic Non-Marine Fish

In Australia the known fossil fish from the Triassic have all been found in non-marine deposits. The known fish faunas are very rich, with more than 30 genera and species. Assemblages from the earliest Triassic, Induan-Olenekian, have been found in the Arcadia Formation of Queensland. the Knocklofty Formation, the Tasmania Basin near Hobart that are fluvial-lacustrine deposits, and from Western Australia, the Blina Shale. Among the fish from these deposits are a number with a global distribution such as Saurichthys, a predator with a long snout and an eel-like body that grew to more than 1 m long, Acrolepis a palaeoniscoid (primitive ray-finned fish) and elements of the skulls and toothplates of many lungfish that have been assigned to a number of taxa such as Apheldus anapes, Namatozodia piticanta and Ptychoceratodus philippsi, a fish with a wide geographic distribution.

According to Kear & Hamilton-Bruce the Sydney Basin has produced the best-known fish material from the Australian Triassic. Many specimens have been found in the Terrigal Formation near Gosford, to the north of Sydney, from the Early to Middle Triassic (Olenekian-lower Anisian), such as sharks, lungfish and actinopterygians (ray-finned fish), that in many cases were of whole fish impressed onto a single rock layer. Included among the described taxa was Xenacanthus, a cosmopolitan shark from freshwater and the lungfish Gosfordia truncata, a deep-bodied form that has been found in deposits up to the Hawkesbury Sandstone from the Middle Triassic. Primitive actinopterygians dominated much of the the rest of the fish fauna from the Terrigal Formation. Among these are Saurichthys gracilis, a saurichthyid, Apatolepis australis and Myriolepis latus, palaeoniscoids that were endemic, several species of Palaeoniscum, a taxon that has also been found in deposits from the Palaeozoic-Triassic in Europe, North American and Asia. Cleithrolepis granulata, a perleidiform and Semionotus, that was widely distributed.

Some of these, such as Cleithrolepis, Myriolepis and Palaeoniscum have also been found in the Hawkesbury Sandstone and the Ashfield Shale of the Wianamatta Group. Many forms that Kear & Hamilton-Bruce consider important have been found in the St. Peters Quarry in western Sydney.

According to Kear & Hamilton-Bruce, among these are a range of diverse palaeoniscoids - Agecephalichthys, Belichthys, Leptogenichthys, Megapteriscus and Mesembroniscus; endemic redfieldiiforms Brookvalia gracilis and Geitonichthys ornatus, Brookvaliidae; a redfieldiid that is also found in North America and South Africa; from the perleidiforms, Manlietta crassa and Procheirichthys ferox; Enigmatichthys attenuatus, a semionotiform, and Promecocosmina formosa, a parasemionotiform, both of which are actinopterygians.

There are also well-preserved fossils of lungfish, Gosfordia truncata and Ariguna formosa and Saurichthys parvidens, a saurichthyid. The Ashfield Shale at St. Peters is the only deposit in which sharks have been found, where an almost complete specimen that was more than 1.5 m long was recovered and assigned to the xenacanthids, Xenacanthus parvidens. The Leigh Creek Coal Measures in South Australia is the only deposit from which fish fossils of Late Triassic age have been recovered from intramontane swamp deposits. This specimen, Leighiscus hillsi,  from the Carnian-Norian is a tail section on which are scales in a distinctive pattern. The taxonomic affinities of this fish are uncertain.

Sources & Further reading

1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.