Marine Creatures of the Cretaceous

Queensland Museum

The different marine faunas originated in a series of inland seas, which formed across central eastern Australia between 140 and 100 million years ago, and which mirror fluctuations in sea levels around the world. The vast shallow inland seas, teeming with life, are the most characteristic feature of the Cretaceous Period in Queensland.

Fossil sponge, Purisiphonia clarkei. This sponge species from the Wallumbilla Formation in southern Queensland, dates to the third inland sea, 115 million years ago. It is the only sponge known from the inland seas that once covered most of the Great Australian Basin.

The third and largest inland sea formed about 115 million yeas ago. At this time the sea level was so high that it covered nearly one quarter of the Australian continent, creating a series of islands. The thick sediment layer deposited during this inland sea now forms the most extensive and fossil-rich unit of marine rocks in the Great Australian Basin.

Ammonites were the dominant group of swimming invertebrate animals in the third inland sea. Some ammonites attained massive sizes, up to 60cm in diameter, and the were adorned with a variety of nodes and ribs, and often had irregular coiling.

Bivalve mollusc, Leionucula quadrata. The fauna of the third inland sea was dominated be bivalves and more than 25 species have been recognised.

Early Cretaceous Fishes
Bony fishes, which had evolved in the Palaeozoic Era, radiated strongly through the Mesozoic, alongside sharks which have skeletons of cartilage.  Many new species evolved in the shallow seas produced by global sea level changes and this also occurred in the Cretaceous seas of Queensland.

Cooyoo australis, skull and skeleton. This specimen is in resin, which supports fragile bones during extraction and also preserves the original alignment of the fish in the rock.

The Queensland fauna is significant because it not only provides information about different groups of fishes, but also adds to understanding of the early evolution of the bony fishes. The Queensland fossils further indicate the southern extent of the global distribution.

Conjoined vertebrae from a cretaceous shark Lamna daviesi

Among the most common fossils in the Early Cretaceous rocks of the Great Australian Basin are small bullet-like objects called belemnites. Living belemnites were cephalopod molluscs, related to squid. They had tubular bodies, with squid like arms and a propulsion vent.

Credits: Story

Images and text from: In Search of Ancient Queensland.
Principal Authors: Dr Alex Cook and Dr Andrew Rozefelds.
Published by the Queensland Museum, 2015
Photographer: Peter Waddington.

Credits: All media
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