| 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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