Australia: The Land Where Time Began

A biography of the Australian continent 

Late Cretaceous Marine and non-Marine Invertebrates

A large amount of information has been collected on the macroinvertebrates of the Late Cretaceous in Australia, comprehensive data on the overall diversity of the fauna as well as the relationships in several assemblages that have been well preserved. Marine deposits have provided the vast majority of the fossils, though the Winton Formation contained a few freshwater bivalves - Pledgia, Hyridella, Megalovirgus, Alathyria, and gastropods (Melanoides) and insects - a dragonfly (Aeschnidopsis flindersiensis), and a mecopteran fly, have been identified.

The Walangarlu Mudstone and the Moonkinu Formation, both parts of the Bathurst Island Group, are sites were the best known macroinvertebrates of the Cenomanian are found, including about 25 genera and species of molluscs that include - bivalves, gastropods, scaphopods and cephalopods. Some common forms that are present in the Bathurst Island Group have also been found in deposits from the Lower Cretaceous, bivalves such as Panopea, Nuculana and  Inoceramus. The bivalve Nemocardium and the gastropod Arrhoges make their first appearance in these deposits. Ammonite assemblages are rich in the Bathurst Island Group deposits, that include a number of genera that have a global distribution that include Acanthoceras, Euomphaloceras, Hamites, Scaphites, Sciponoceras and Turrilites. It is suggested  by the authors3 that as some species from North Australian have been found in North Africa, Madagascar (such as Scaphites dailyi) and Europe Turrilites costatus), it is probable this indicates open sea connections.

The limited number of outcrops of rocks from the Coniacian and Turonian has meant that assemblages from these time periods are not well known but they include ammonites such as Collingnoniceras. This genus from the Turonian, widespread in the Northern Hemisphere, is present in the Moonkinu Formation. There is virtually no knowledge of the benthic invertebrates of the Turonian-Coniacian. Up to 8 genera of bivalves are present in the Molecap Greensand and Gingin Chalk, including the widespread Gryphaea and Inoceramus (well-known in the Northern Hemisphere), the extant oyster Ostrea, and what the authors3 suggest may be the earliest specimens known of the present-day scallop Spondylus. There are also sponges, Porosphaera, brachiopods, Boucharidella, Kingena and Inopinarticula, ammonites such as Baculites, sea urchins, Cidaris, and crinoids lacking stalks, Uintacrinus and Marsupites. According to the authors3 age ranges for the Gingin Chalk are provided by the latter genus as they correlate with Europe and North America. The assemblages of the Molecap Greensand and Gingin Chalk, in spite of their cosmopolitan nature, are suggested by the authors3 to herald the appearance of southern high-latitude kossmaticeratid ammonites that are distinctive such as Kossmaticeras, also suggesting it could indicate the onset of lower temperatures, a trend that continued in the southern part of the Perth Basin, at least, into the latest part of the Cretaceous.

In these deposits the macroinvertebrate assemblages are among the richest known from Australia. The situation is very different in the fossil record of the Campanian where they are almost unknown. More than 44 benthic mollusc genera have been found in the Miria Formation, including gastropods, bivalves and scaphopods, nearly all have been reported from the Tethyan Ocean realm to the north, suggested by the authors3 to indicate the presence of warmer waters. A high proportion of infaunal or burrowing bivalves has been reported from the Miria Formation, such as Trigonia and Panopea, as well as free-swimming pectinids, scallops such as Chlamys and Giraliapecten suggested to probably indicate shallow water. There is a high level of diversity among the ammonites of the Miria Formation with more than 30 genera and 88 species, including a mixture of southern high-latitude genera such as Kossmaticeratids, Gunnerites, as well as elements that are known from northern warm waters, Pachydiscus and Eubaculites and Baculites, that both had strait shells. The authors3 suggest the latter appear to have been derived from assemblages in southeastern Africa, and in particular India that were of contemporary ages. The presence of these cephalopods together with other cosmopolitan cephalopods such as Cimomia, a nautiloid, the authors3 suggest they support the view that the marine faunas of the latest  Cretaceous in Australia were latitudinally transitional, being comprised of forms from the cooler waters in the south and warmer waters to the north.





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