New Fossil Crowned The King Of Trilobites

It may have been only the size of a house cat, but the trilobite Redlichia rex was the terror of the Cambrian era, crushing the shells of smaller trilobites. Katrina Kelly 2019

Trilobites not only achieved world domination but they managed to hang onto that status for a long time – much longer, for example, than the dinosaurs. Many different species participated in this reign. A newly identified example has been given the name Redlichia rex because it reminded its discoverers of Tyrannosaurus rex, its size and weapons making it the king of the Cambrian Era.

You might not think Redlichia rex is a particularly terrifying beast, since it only grew to between 30 and 35 centimeters (12 and 14 inches) long. In its day, however, such size made a creature a giant. R. rex was found in the Emu Bay shale deposit on Kangaroo Island, South Australia, and is approximately twice the size of any other Australian trilobite from the era's 56-million-year span.

It wasn't just size that would have made R. rex intimidating, according to University of Adelaide PhD student James Holmes. It came with spines on its legs that appear to have evolved to crush the shells of its prey. “Trilobites usually have some sort of appendage with spines, but the smaller ones don't have this shape,” Holmes told IFLScience. “Those tend to be longer and more pointy, where as [rex's] were shorter and more robust, more similar to those we see on horseshoe crabs or species from the Burgess Shale.”

Redlichia rex beautifully preserved in the Emu Bay Shale. James Holmes

Holmes suspects R. rex used these shell crushers to prey on smaller trilobites. Indeed, Dr Diego Garcia-Bellido, senior author with Holmes of the paper in the Journal of Systematic Palaeontology describing the discovery, said in a statement: “Interestingly, trilobite specimens from the Emu Bay Shale – including Redlichia rex – exhibit injuries that were caused by shell-crushing predators.”

Perhaps something even bigger was preying on Emu Ba's trilobites, but Garcia-Bellido and Holmes also think R. rex may have been a cannibal, and the smashed shells may have been destroyed by the lethal spines of members of its own species.

Although we have abundant fossils of trilobite shells, the soft parts are seldom preserved. R. rex is an exception, with antennae and legs captured in exquisite detail several times, something Holmes attributes to a low-oxygen environment, which prevented rotting before the dead individuals were buried in sediments.

Our window on the Cambrian Era is narrow both in space and time. Holmes told IFLScience the Emu Bay Shale is the only known deposit from the era in the entireSouthern Hemisphere. As a result, we don't know how R. rex's reign of terror ended. Dating to 500 million years ago, it was a relatively early arrival among the trilobites. Holmes doesn't know whether it was displaced by a relative or wiped out in one of the Cambrian era's multiple extinction events.

 

 

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