Three-eyed shrimp from half a billion years ago have the world’s oldest brain

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The world’s oldest brain was found in the remains of a three-eyed shrimp that swam the oceans more than half a billion years ago.

Its entire central nervous system is still visible – allowing unprecedented insight into the ancestors of insects, spiders and crustaceans.

It was named Stanleycaris hirpex and described as “the stuff of nightmares”. It had two eyes “on stalks” with a larger one in the middle – and spiky claws.

It lived during the Cambrian “Explosion” – a period of rapid evolution when most of the large groups of animals appear in the fossil record.

The creature was one of the radiodonts, apex predators that were known as the “great whites” of their day.

At over a meter long, they were a species of early arthropods — creepy crawlies with jointed limbs.

Despite Stanleycaris’ bizarre appearance, it’s the contents of its head that excites scientists the most.

84 individuals unearthed in Burgess Shale, a prehistoric cemetery in Canada’s Rocky Mountains, still have their brains and nerves intact – after 506 million years.

Lead author Joseph Moysiuk, a graduate student at the University of Toronto, said: “We can even see visual processing centers feeding the large eyes and traces of nerves entering the limbs.

“The fine details are so clear, it’s like looking at an animal that died yesterday.”

The new specimens give an insight into the nervous system of the ancestors. Finding fossilized soft tissue is rare – but this is unique.

Most of the fossils we have are bones and/or hard body parts like teeth or exoskeletons.

Brains and nerves are made of fat-like substances that don’t normally survive.

The central nervous system coordinates all neural and motor functions. In vertebrates, it consists of the brain and spinal cord.

In arthropods, the brain is more condensed with a chain-like array of interconnected neural tissue masses resembling a string of pearls.

The brain of Stanleycaris consisted of two segments, the protocerebrum and the deuterocerebrum.

They were connected to the eyes or the forehead claws – and today they control the visual and antennae signals in arthropods.

Mr. Moysiuk of the Royal Ontario Museum added: “We conclude that a bisected head and brain have deep roots in the arthropod lineage.

“Its development likely predates the three-segmented brain that characterizes all living members of this diverse animal phylum.”

EMBARGO FRI 1600: The world's oldest brain has been found in the remains of a three-eyed shrimp that swam the oceans more than half a billion years ago

This little guy’s brain is still here after half a billion years (Credit: SWNS)

In modern arthropods – like grasshoppers and other insects – the brain also has a tritocerebrum.

It is connected to the labrum, a movable upper lip, and integrates sensory information from the other two lobes of the brain. An extra subject has radical implications.

Repeated copies of many arthropod organs can be found in their segmented bodies. Working out how they line up is key to understanding diversification.

Mr Moysiuk said: “These fossils are like a Rosetta stone, helping to link features in radidonts and other early fossil arthropods with their counterparts in surviving groups.”

In addition to a pair of stalked eyes, Stanleycaris had a large central pipit on the front of its head – a feature never before seen in a radiodont.

Co-author Professor Jean-Bernard Caron, Mr Moysiuk’s supervisor, said: “The presence of a giant third eye in Stanleycaris was unexpected.

“It emphasizes that these animals looked even more bizarre than we thought. It also shows us that the earliest arthropods had already evolved a variety of complex visual systems, like many of their modern relatives.”

He added: “Since most radiodonts are known only from scattered fragments, this discovery is a crucial leap forward in understanding what they looked like and how they lived.”

During the Cambrian period, radiodonts were among the largest animals. Also called the “strange wonder,” Anomalocaris was at least 3 feet 3 inches tall — making it a sea monster.

At no more than eight inches, Stanleycaris was much smaller. But it would have been a formidable killer – at least three times the size of most rivals.

Radodont means “radiant teeth”. The unusual animals were named for their toothy, rounded jaws. They were adapted to the faint light of deep water.

Stanleycaris’ sophisticated sensory and nervous systems would have allowed it to efficiently seek out small prey in the dark.

Mr Moysiuk added: “With large compound eyes, an impressive-looking round mouth lined with teeth, front claws with an impressive array of spikes, and a flexible, segmented body with a row of armbands on its sides, Stanleycaris would have been the stuff of nightmares.” for every little ground dweller unfortunate enough to cross his path.’

The study in Current Biology is based on an analysis of a previously unpublished collection of 268 Stanleycaris specimens.

Most were collected in the 1980s and 1990s from layers above the famous Walcott Quarry in Yoho National Park, British Columbia.

They are part of the extensive collection of fossils from Burgess Shale – a World Heritage Site – housed at the Royal Ontario Museum.

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Justin Scacco

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