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Fossils show sea creature's half-billion-year-old brain

Ancient brain Spectacular fossils unearthed in China show detailed brain structures of a bizarre group of sea creatures that were the top predators more than half a billion years ago.

The discovery of the near-complete fossils of the animal called Lyrarapax unguispinusis reported in the journal Nature.

The ancient animal lived during the Cambrian Period, a pivotal juncture in the history of life on Earth when many major animal groups first appeared.

It was a member of a group known as anomalocaridids -- primitive relatives of arthropods, which include crustaceans, insects and spiders -- that hunted prey with a pair of claw-like grasping appendages in front of the eyes.

Even though anomalocaridids do not have any direct descendants alive today, the brain structures of Lyrarapax closely resemble those of worm-like animals called velvet worms that crawl along the ground in tropical and semitropical forests in the southern hemisphere.

The researchers say the similarities suggest that velvet worms may be very distant cousins of the anomalocaridids, whose best-known example is Anomalocaris, known from a Canadian fossil site called the Burgess Shale.

Velvet worms, land animals also known as onychophorans, grow to a few inches in length, have two long feelers extending from the head and have numerous pairs of stubby, unjointed tubular legs that each end in a pair of small claws.

Spiny-clawed, lyre-shaped predator

Lyrarapax, whose scientific name means spiny-clawed, lyre-shaped predator, lived 520 million years ago. Its neuroanatomy resembles that of velvet worms in multiple ways, with a simple brain and a pair of ganglia -- a cluster of nerve cells -- placed in the front of the optic nerve and the base of the grasping appendages.

The soft parts of any animal's body typically decay after death, meaning that fossils usually preserve only hard parts like bones, teeth and shells. But under exceptional circumstances, soft tissue and anatomical organs can be preserved in fossils.

Lyrarapax was much smaller than some other anomalocaridids. It measured about 15 centimetres long, roughly the size of a large prawn.

The three specimens of Lyrarapax that were found "may represent immature stages of the animal, so it might be larger," says the paper's lead author Peiyun Cong, a paleontologist at Yunnan University.

"Anomalocaridids preserved with the whole body are very rare. None of them have been reported with the brain," says Cong.

The fossils show that anomalocaridids possessed brains that were less complex than those of animals it may have hunted.

University of Arizona neuroscientist Nicholas Strausfeld, another of the researchers, says the threat posed by predators like these creatures may have helped drive brain complexity among animals in the ancient seas.

"Predation may have in part contributed to the evolution of more elaborate brains that could process more complex ecological cues that might have offered camouflage or other protection," says Strausfeld.