Australia: The Land Where Time Began

A biography of the Australian continent 

Marine Reptiles

Marine reptiles are not well known in Australia.

Pliosauridae

These were short-necked, long-snouted with robust bodies.

Indeterminate indeterminate from the Early Jurassic near Mt Morgan, northern Queensland. It is known from isolated vertebrae, along with the Kolane specimens, are the equally oldest-known sauropteyrgians in the world. The bone has been weathered out of the conglomerate rocks, the fossils being casts of the mould remaining in the rocks.

The vertebrae are about 6 cm wide with deep transverse processes. The centra have a diameter of about 6 cm. The vertebrae are believed to be related to those of the English form Leptocleidus. Later it was suggested they were closer to a new genus from the Jurassic Oxford Clay in England.

Indeterminate indeterminate, Uppermost Early Jurassic Westgrove Ironstone member of the Evergreen Formation on Kolane Station, south central Queensland.

Elasmosauridae

These were long-necked plesiosaurians with 72 neck vertebrae.

Indeterminate indeterminate, Middle Jurassic, from the Colalura Sandstone, at the Bringo Cutting 20 km east of  Geraldton, western Australia.  It is known from vertebrae, the best specimen is a pectoral vertebra from the oldest elasmosaurid known in Australia.  The vertebrae were found in coarse sandstone deposited in a shallow sea environment, possibly near a river mouth, because of the presence of dinosaur remains in the same deposit.

It had a very wide centrum 63 mm in diameter and 42 mm high in the midline.

Ophthalmosauridae

The ichthyosaur Platypterygius australis lived in the Eromanga Sea, the epicontinental sea that covered vast areas of central Australia between 120 and 90 million years ago. It was a large-bodied ophthalmosaurid that grew to about 7 m. It had a low-crowned skull and its long snout contained up to 200 conical teeth, the roots of which were quadrangular in cross-section. It had small orbits and a long post-orbital region.

Platypterygius longmani

This species differed from other members of the genus in the structure of the external nares, humerus, forefin and vertebrae. Fossils of P. longmani have been found throughout the area covered by the Eromanga Sea. White Cliffs in New South Wales and the Bulldog Shale of South Australia are the most significant of the sites.

At the time Platypterygius swam in the Eromanga Sea Australia was in high latitudes near the South Pole, so that the water would have been cool to cold. Glendonites and boulders have been found that are believed to have been ice-rafted, indicating that the Australian winters of the time were very cold. They are thought to have eaten fish and marine invertebrates such as squid, and one fossil from South Australia had a number of whole belemnites in the stomach region.

Like all ichthyosaurs, Platypterygius gave birth to live young, several fossils have been found that were in the process of giving birth when they died. A number of young specimens about 2 m long have also been found in South Australia.

Links

• The Australian Museum - Platypterygius australis
• Australian Mesozoic Marine Reptiles
• Australian Museum Marine Reptiles
• Adelaide Research & Scholarship
• Cretaceous Research
• British Library Direct

Sources & Further reading

1. Long, John A, 1998, Dinosaurs of Australia and New Zealand, University of New South Wales Press.