The fossils belong to a long-extinct group of trilobites — the ancestors of modern crustaceans and insects — which had calcified, armour-like skeletons.
Researchers described the new species as the “T-Rex of the trilobites” — even naming it Redlichia rex in homage to the iconic dinosaur.
At 30cm the Redlichia rex is the largest Cambrian trilobite ever discovered in Australia — double the size of other trilobites — and blessed with a physique made for eating and killing.
It’s believed the species was at the forefront of the Cambrian explosion and developed unique features as a result of an evolutionary “arms race” between predators and prey.
The Cambrian explosion refers to an event that occurred approximately 541 million years ago when complex animals with mineralised skeletal remains suddenly appeared.
Head researcher James Holmes, a PhD student with the University of Adelaide’s School of Biological Sciences, said the Redlichia rex was an example of trilobites developing more effective measures of attack and defence, such as the evolution of shells.
“The overall size and crushing legs of Redlichia rexare a likely consequence of the arms race that occurred at this time,” Mr Holmes said.
“(It had) formidable legs with spines used for crushing and shredding food, which may have been other trilobites. This giant trilobite was likely the terror of smaller creatures on the Cambrian sea floor.”
The new species was discovered at the Emu Bay Shale on Kangaroo Island, a world-renowned deposit for this type of preservation.
Associate Professor Diego García-Bellido, from the University of Adelaide and the South Australian Museum, said many of the trilobite fossils from Emu Bay Shale — including Redlichia rex — exhibit injuries inflicted by “shell-crushing predators”.
“There are also large specimens of fossilised poo (or coprolites) containing trilobite fragments in this fossil deposit,” Prof Garcia-Bellido said.
“The large size of injured Redlichia rex specimens and the associated coprolites suggests that either much bigger predators were targeting Redlichia rex, such as Anomalocaris — an even larger shrimp-like creature — or that the new species had cannibalistic tendencies.”
Mr Holmes’ team included researchers from University of Adelaide, South Australian Museum and the University of New England. Their findings have been published in the Journal of Systematic Palaeontology.
Meanwhile, the public can view specimens of Redlichia rex and other Emu Bay Shale fossils at the South Australian Museum.