|SIZE||Juevenile 5.6 metres (18 feet) long,
adults c.7 metres (23 feet) long
Ichthyosaur remains were first discovered in Australia in 1865 by James Sutherland on the Flinders river in Queensland. Since then several other finds have been found in Queensland, Western Australia and the Northern Territory, all of which may be attributed to a single species. Originally described as Ichthyosaurus australis, they have since been attributed as a species of Platypterygius (Platypterygius australis), more recently refered to as Platypterygius longmani. A member of the Stenopterygidae family, these ichthyosaurs are characterised by their broad front flippers, due to the presence of multiple accessory digits, for which they are known as longipinnate ichthyosaurs.
The most complete specimen was found on Telemon station in 1934. It lacks all but one tail fin vertebra, the pelvic girdle and hindlimbs, parts of the pectoral girdle and some ribs. The skull and most of the vertebrae are intact, as is the left humerus, with the entire right forelimb being almost complete but poorly reconstructed. It would have been a sub-adult about 5.6 metres (18 feet) long. A larger specimen, known as the Kilterry ichthyosaur, may represent an adult of the species, and probably reached about 7 metres (23 feet) in total length.
A series of CAT scans performed on a juvenile specimen of Platypterygius in 2001 indicate that they were almost certainly deaf. However they may have had other means of detecting vibrations in the water, such as sharks do using "lateral lines" that run the length of their bodies.
The similarity between ichthyosaurs and modern dolphins suggests that ichthyosaurs were extremely well adapted to life in the seas. Several adaptations would have been useful for an air breathing marine creature. The front flippers may have been quite mobile, enabling ichthyosaurs to make rapid corrections to keep themselves on course, or to manouver and stop suddenly while chasing prey. Their downward curving beak probably allowed them to surface for air without the need for the snout to completely break the surface, reducing drag so as not to slow the creature down while it was travelling. The tail vertebrae bent downwards suddenly at the very tip at an angle of about 40 degrees, which served as reinforcing for the lower lobe of the tail. This is the opposite of that seen in sharks, where the vertebrae continue into the upper lobe of the tail. They seemed to have prefered the shallow coastal shelves rather than venturing into deep ocean, perhaps to allow them to rest on the ocean floor like modern marine turtles or sea snakes yet remain in close proximity to the surface when they needed to take a breath.
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