Fossils of giant new species of sea creature found on South Australia's Kangaroo Island

The fossils of a giant new species of sea creature have been found on Kangaroo Island, with experts saying it was likely the "terror" of other creatures on the seafloor.

Researchers said the discovery of a group of sea creatures called trilobites added insights to knowledge of the Cambrian explosion, the greatest diversification event in the history of life on Earth.

The fossils, called Redlichia rex, were the largest Cambrian trilobite to be discovered in Australia.
Trilobites, which had hard, calcified, armour-like skeletons over their bodies, were related to modern crustaceans and insects.

They were one of the most successful fossil animal groups, surviving for about 270 million years.
The new species was discovered at Emu Bay on Kangaroo Island, where more than 100 other species were discovered, including some with soft parts intact.

"We decided to name this new species of trilobite Redlichia rex — similar to Tyrannosaurus rex — because of its giant size, as well as its formidable legs with spines used for crushing and shredding food, which may have been other trilobites," University of Adelaide PhD student James Holmes said.

The findings were published in the Journal of Systematic Palaeontology by a team of scientists from the University of Adelaide, South Australian Museum and the University of New England led by Mr Holmes.

A giant of the ancient ocean

Redlichia rex is the largest Cambrian trilobite found in Australia, growing to about 30 centimetres long — or twice the length of other trilobites of about the same age.

"Interestingly, trilobite specimens from the Emu Bay Shale — including Redlichia rex — exhibit injuries that were caused by shell-crushing predators," said senior study author Associate Professor Diego Garcia-Bellido, from the University of Adelaide and the South Australian Museum.

"There are also large specimens of fossilised poo — or coprolites — containing trilobite fragments in this fossil deposit."

Mr Holmes said one of the major drivers of the Cambrian explosion was likely an evolutionary "arms race" between predators and prey.

"The overall size and crushing legs of Redlichia rex are a likely consequence of the arms race that occurred at this time," Mr Holmes said.

Specimens of Redlichia rex and other Emu Bay Shale fossils are on display in the South Australian Museum.