Recently-examined fossil evidence in 2006 suggested
that Australia was once home to ancient reptiles which swam in huge
The large, carnivorous reptiles lived 115 million
years ago, in the very middle of the long period of dominance of the
planet by dinosaurs, when much of the continent was covered in water.
Fossils of two then-new species of plesiosaur were discovered near
Coober Pedy in South Australia.
These specimens were described in editions of the
journals, Biology Letters and Palaeontology. One is known as
Umoonasaurus demoscyllus, and this was about 2.4m long (7.2
feet) with had crests on its head. It may have used these for display
or mating purposes, a common-enough behaviour.
The lead author of the two papers, Dr Benjamin Kear
of the University of Adelaide, suggested imagining a compact body
with four flippers, a reasonably long neck, small head, and short
tail, much like a reptilian seal.
The other species, Opallionectes andamookaensis,
grew to about 5m in length (16 feet) and had small needle-like teeth.
Something like thirty fossils were discovered at
an opal mine near the outback mining town of Coober Pedy. They were
made up of the mineral opal, which filled the spaces left by bones
when the original fossil-bearing rock was dissolved away by acidic
The fossils included several skeletons and a complete
skull of Umoonasaurus, plus a partial skeleton of
They were thought to be examples of juvenile
animals, suggesting that the lake was a breeding and nursery ground.
The researchers behind the project stated in their
report that they believed the sea-dwelling adults returned to the
shallow inland waters to breed and raise their young (much as many
aquatic mammalian species do today). They were carnivorous, feeding
on fish and squid.
At the time, Australia was much colder, still
connected as it was to Antarctica as part of the fracturing
super-continent of Gondwana and being located closer to the South
Pole. The inland ocean would have frozen over in places during the
winter. However, the creatures may have evolved mechanisms to cope
with the harsh climate, such as a faster metabolic rate.