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Life was weird 500 million years ago

With its circular jaw armed with an array of fearsome teeth, it cruised the prehistoric seas as one of the top marine predators of its day.

Now scientists have been able to piece together the bizarre jigsaw puzzle that is Hurdia victoria – an ancestor of arthropods such as insects, spiders and crustaceans. The 1.5ft-long sea monster belonged to a group of weird animals that lived 500 million years ago during a period known as the "Cambrian explosion", when life on Earth went through a burst of evolutionary diversity.

The first fossilised scraps of Hurdia were discovered in 1912. These were followed by further body parts that were so varied and unusual that they were incorrectly classified as either jellyfish, sea cucumbers or shrimp-like crustaceans.

The recent discovery of complete body imprints in fossilised rock has enabled scientists to reconstruct the predator in all its glory - including a mysterious shell-like carapace positioned in front of its head.

"This structure is unlike anything seen in other fossil or living arthropods," said Allison Daley of Uppsala University in Sweden.

"We can only guess at what its function might have been."