Last updated June 17, 2019 at 5:14 pm
Fossils belonging to a long-extinct group of sea creatures have been found on Kangaroo Island, dating to the Cambrian explosion over 500 million years ago.
Trilobites, which had hard, calcified, armour-like skeletons over their bodies, are related to modern crustaceans and insects.
They are one of the most successful fossil animal groups, surviving for about 270 million years (521 to 252 million years ago). Because of their abundance in the fossil record, they are considered a model group for understanding evolution over the period.
Largest Cambrian trilobite discovered in Australia
The new species is about 500 million years old, and is the largest Cambrian trilobite discovered in Australia. It grew to around 30 cm in length, which is almost twice the size of other Australian trilobites of similar age.
“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,” says lead researcher James Holmes from the University of Adelaide.
The preservation of trilobite ‘soft parts’ such as the antennae and legs is extremely rare.
Insight into Cambrian explosion
The finding is adding important insights to our knowledge of the Cambrian ‘explosion’, the greatest diversification event in the history of life on Earth, when almost all animal groups suddenly appeared over half-a-billion years ago.
“Interestingly, trilobite specimens from the Emu Bay Shale – including Redlichia rex – exhibit injuries that were caused by shell-crushing predators,” says García-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. 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.”
Evolutionary arms race between predators and prey
One of the major drivers of the Cambrian explosion was likely an evolutionary “arms race” between predators and prey, with each developing more effective measures of defence (such as the evolution of shells) and attack.
“The overall size and crushing legs of Redlichia rex are a likely consequence of the arms race that occurred at this time” says Holmes. “This giant trilobite was likely the terror of smaller creatures on the Cambrian seafloor.”