A giant prehistoric shrimp-like monster which terrorised the oceans more than half a billion years ago has been discovered by scientists.

The fearsome-looking beasts, known as anomalocaridids, grew up to 6ft long and - unlike today's prawns - could bite back, using its razor-sharp teeth to crack open shellfish.

They were already believed to be the largest animals of the 'Cambrian' period which first spawned our complex ecosystem.

© AFP/Getty ImagesPrawn to be wild: A recreation of a anomalocaridids, fearsome beasts that killed their prey using giant sharp teeth

But now palaeontologists in Morocco have discovered they were much larger than first though and lived 30million years longer than first thought.

They dug up a giant fossil measuring a just over 3ft long - more than 12in bigger than other finds.

Previously found specimens of the marine predators had dated between 540 and 500million years old.

But this latest discovery was found among a trove of remains including thousands of examples of soft-bodied marine fauna dating back to about 488 to 472 million years ago.

This means they may have been larger than first thought as they developed for a much longer period of time.
© AFP/Getty ImagesProof: This giant fossil was unearthed in Morocco among remains of other marine fauna dating back to about 488 to 472million years ago. It means the anomalocaridids lived 30million years longer that experts had first thought

The iconic anomalocaridids had large limbs resembling shrimp tails and a big mouth on the undersurface of the head.

They also had large eyes and a ring of sharp teeth that could close in like nippers to crack shellfish.

The new fossil, described in the journal Nature, also reveals a series of blade-like filaments in each segment across the animal's back which could have functioned as gills.

And it dates back to the Ordovician period, a time of intense biodiversification that followed the Cambrian meaning these animals existed for 30million years longer than had been realised.

Dr Derek Briggs, director of the Yale Peabody Museum of Natural History in Connecticut, said: 'The anomalocaridids are one of the most iconic groups of Cambrian animals.

'These giant invertebrate predators and scavengers have come to symbolise the unfamiliar morphologies displayed by organisms that branched off early from lineages leading to modern marine animals and then went extinct. Now we know they died out much more recently than we thought.'

They would have inhabited a muddy sea floor in quite deep water and were trapped in sediment clouds that buried them and preserved their soft bodies.

After death anomalocaridids and similar creatures tended to disintegrate and fall apart into separate chunks, and completely intact fossil remains are very rare.

Co-researcher Dr Peter Van Roy, now at Ghent University in Belgium, said: 'The new discoveries in Morocco indicate animals characteristic of the Cambrian, such as the anomalcaridids,ued to have a considerable impact on the biodiversity and ecology of marine communities many millions of years later.'