Australia: The Land Where Time Began

A biography of the Australian continent 

Jurassic non-marine Invertebrates

Marine deposits from Western Australia make up almost all of the known fossil record of the macroinvertebrates from the Australian continent. Some rare insects and freshwater bivalves such as Prohyria sceptici and Prosphaerium talbragarensis are known from other locations such as the Evergreen Formation, Queensland, of Pliensbachian-Toarcian age and from Western Australia, the Cockleshell Gully Formation, near Korumburra, Victoria, from the Lower Jurassic and the Talbragar Beds, New South Wales, from the Upper Jurassic.

Little is known of marine macroinvertebrates from Australia in the Early Jurassic, though there is more known of the highly diverse assemblages from the Middle Jurassic found in a number of units, such as the Newmarracarra Limestone near Geraldton, southwestern Western Australia. In these strata the macroinvertebrates found are mostly bivalves and ammonites, most of which are members of lineages that are Tethyan or cosmopolitan. With few exceptions most of the species-level taxa are endemic, leading to the suggestion by Kear & Hamilton-Bruce that the fauna in the Newmarracarra Limestone inhabited an isolated environment, possibly a narrow embayment that extended in a southwesterly direction between the Indian and Australian parts of Gondwana. The dominant bivalves are shallow water forms that include infaunal or burrowing trigonids, Trigonia, hard surface cementers such as the oysters Astarte and Gresslya, and pectinids that are free swimming, scallops such as Pecten. Nautiloids (Nautilus), belemnites, that were squid-like (Dicoelites) and ammonites.

Among the ammonites there was a mix of cosmopolitan and endemic genera. Fontannesia, Otoites, Sonnonia were cosmopolitan while Pseudotoites had a circum-pacific distribution. Newmarracarroceras was endemic. Kear & Hamilton-Bruce suggest this indicates palaeobiogeographical links with southeast Asian (Indonesian) and the west coast of the Americas, North America, Argentina.

The Alexander Formation and the Jarlemai Siltstone, the Edgar Ranges near Broome in the northwest of Western Australia, both of Oxfordian -Tithoinian age from the Late Jurassic, are the sites from which marine macroinvertebrates are best known in Australia. Included among the fauna from these sites are indeterminate ophiuroids (brittle stars), as well as taxa of distinctive belemnites (Belemnopsis), ammonites (Kossmatia, Virgatosphinctes), and bivalves (Buchia, Calpionella). Kear & Hamilton-Bruce suggest that these Western Australian assemblages support the suggestion of 'an essentially Tethyan faunal extension into the eastern Gondwanan region', as species comparable to those from the Western Australian Late Jurassic sites have previously been described from the South-East Asia (Indonesia).

Sources & Further reading

  1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.
Last updated 14/12/2011 

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