Half a billion years ago, the oceans were filled with life that looked more like aliens than the marine animals we know today.

Now, researchers have uncovered the fossil of an unusual creature that was likely a giant compared to tiny ocean life 500 million years ago.

Radiodonts, a group of primitive arthropods, were widespread after the Cambrian explosion event 541 million years ago – a time when a multitude of organisms suddenly appeared on Earth, based on the fossil record.

The newly discovered fossil belonged to Titanokorys gainesi, a radiodont that reached 1.6 feet (half a meter) in length – which was huge, compared to other ocean creatures that were about the size of a pinkie finger.

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The fossil was found in Cambrian rocks from the Kootenay National Park, located in the Canadian Rockies. A study detailing the fossil published Wednesday in the journal Royal Society Open Science.

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“The sheer size of this animal is absolutely mind-boggling, this is one of the biggest animals from the Cambrian period ever found,” said study author Jean-Bernard Caron, the Royal Ontario Museum’s Richard M. Ivey Curator of Invertebrate Palaeontology, in a statement.

Titanokorys would have been a bewildering animal to encounter. It had multifaceted eyes, a mouth shaped like a pineapple slice that was lined in teeth, and spiny claws located beneath its head to catch prey. The animal’s body was equipped with a series of flaps that helped it swim. And Titanokorys had a large head carapace, or a defensive covering, like the shell of a crab or turtle.

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This is an artist’s illustration reconstructing Titanokorys gainesi as it appeared in life.Lars Fields/© Royal Ontario Museum

“Titanokorys is part of a subgroup of radiodonts, called hurdiids, characterized by an incredibly long head covered by a three-part carapace that took on myriad shapes. The head is so long relative to the body that these animals are really little more than swimming heads,” said study coauthor Joe Moysiuk, a Royal Ontario Museum-based doctoral student of ecology and evolutionary biology at the University of Toronto, in a statement.

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Researchers are still trying to understand why some radiodonts had such a variety of head carapaces, which came in all shapes and sizes. It’s unclear what this head gear was protecting them from, given their size compared to other sea life at the time. In the case of Titanokorys, the broad, flat carapace suggests it had adapted to live near the seafloor.

“These enigmatic animals certainly had a big impact on Cambrian seafloor ecosystems. Their limbs at the front looked like multiple stacked rakes and would have been very efficient at bringing anything they captured in their tiny spines towards the mouth. The huge dorsal carapace might have functioned like a plough,” Caron said.

The carapace of T. gainesi (lower), along with two symmetrical rigid plates (upper), covered the head from the underside. They formed a three-part set of armor that protected the head on all sides.Jean-Bernard Caron/© Royal Ontario Museum

The fossils of Titanokorys were found in Marble Canyon, located in northern Kootenay National Park, which has been the site of many discoveries of Cambrian fossils dating back 508 million years ago. The site is part of the Burgess Shale, a deposit of well-preserved fossils in the Canadian Rockies. The Burgess Shale is a UNESCO World Heritage Site.

One of those discoveries includes the radiodont Cambroraster falcatus, so named because its head carapace is similar in shape to the Millennium Falcon from Star Wars. It’s possible that these two species scuffled on the bottom of the sea for prey.

Titanokorys, and other fossils collected from Burgess Shale, will be displayed in a new gallery at the Royal Ontario Museum beginning in December.