Australia: The Land Where Time Began

A biography of the Australian continent 

Triassic Invertebrates

Macroinvertebrate faunas of the Australian Triassic are well known, the Ipswich Coal Measures at Mt. Crosby near Brisbane in southeast Queensland being the site of one of the best known, with a very rich insect fossil record. About 50 % of the fossils at this site are of Triassoblatta, one of a number of cockroaches, and there are also several species incorporated in the assemblage that are also found in deposits from the Triassic throughout eastern Australia. There are also sawflies such as Archexyla crosbyi, scorpionflies such as Mesochorista,
a genus common in the assemblages from the Sydney Basin, caddisflies (Cladochoristella bryani), orthopterans such as grasshoppers (Triassolocusta leptoptera that has also been found in the Sydney Basin deposits), dragonflies (odonatans) and beetles (or coleopterans - isolated elytra and wings).

At beacon Hill in the Hawkesbury Sandstone, and in the Ashfield Shale of the Wianamatta Group, at St Peters in the Sydney suburbs,  a well-preserved non-marine invertebrate fauna has been found from the Middle Triassic - Anisian-Landinian. A number of unionoid bivalve types are present (Protovirgus dunstani, P. brookvalensis and Unionella wianamattensis), as well as crustaceans such as the isopod Protamphisopus wianamattensis, and a conchostracan, and a number of insects Clatrotitan, a titanopteran with a wingspan of about 300 mm. In the Leigh Creek Coal Measures, South Australia, of Carnian-Norian age, Prohyria eryensis and Megalovirgus jaenschi, freshwater bivalves, and insect wing impressions have been found that have not been identified. Mesohydridella ipsviciensis, an unionoid bivalve, have been found in the Ipswich Coal Measures, southeast Queensland, that were contemporaneous.

It is very different for marine macroinvertebrates with the fossil record being very limited. The only known assemblages are 4 fossil deposits found in offshore boreholes, in the Kockatea Shale in the Perth Basin from the Lower Triassic and from the Middle Triassic, undifferentiated sediments in the Sahul Shoals off the coast of Western Australia. In the Perth Basin there are outcrops of the Kockatea Shale in the Mt Minchin area, and in southeast Queensland, the Broweena Formation near Maryborough in the Maryborough Basin and the Traverston Formation near Woodnum  in the Gympie Basin, some remains have been found. Included in the deposits of the Kockatea Shale are genera of ammonoids such as Anasibrites, Arctoceras, Glyptophiceras, Gyronites, Hemiprionites, Ophiceras Proptychites and a bivalve, Nuculana, all of which are common to the southern Tethyan Shelf - Afghanistan, Pakistan, Himalayas and Timor, as well as Pacific regions such as Japan and western North America of Gondwana.

The invertebrates in the Broweena Formation and the Traverston Formation correlate with those of the upper Kockatea Shale. They comprise ammonoids of the southern Tethyan/Pacific, with endemic species Anaflemingites armstrongi, Dieneroceras woodumense, Latisageceras woodumense, Paranorites queenslandicus, as well as the bivalve Bakevellia, Nuculanella, indeterminate snails (gastropods)  and brittle stars (ophiuroids). Ammonoids have been found in the Sahul Shoals of Middle Triassic age, tentatively attributed to Nicomedites that has been reported from Asia Minor, Kear & Hamilton-Bruce suggesting it may indicate the deposit is of lower Anisian age.

Sources & Further reading

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