An 'exceptional' 530-million-year-old fossil contains what could be the oldest eye ever discovered, according to researchers.

The remains of the extinct sea creature include an early form of the eye seen in many of today's animals, including crabs, bees and dragonflies.

Experts made the find while examining the well-preserved fossil of a hard-shelled species called a trilobite.

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An 'exceptional' 530-million-year-old fossil contains what could be the oldest eye (right eye circled) ever discovered, according to researchers. Experts made the find while examining the well-preserved fossil of a hard-shelled species called a trilobite

TRILOBITE'S EYES The right eye of the fossil was partly worn away, giving researchers a clear view inside the organ. This revealed details of the eye's structure and function, and how it differs from modern compound eyes. The species had poor vision compared with many animals today but it could identify predators and obstacles in its path, researchers say. Its eye consists of approximately 100 ommatidia, which are situated relatively far apart compared to contemporary compounds eyes, the team says. Unlike modern compound eyes, the fossil's eye does not have a lens. This is likely because the primitive species - called Schmidtiellus reetae - lacked parts of the shell needed for lens formation. Advertisement

Experts from the University of Edinburgh were among the team that made the discovery on a fossil that was unearthed in the Lükati Formation, a layer of rock dating from the Cambrian era, in northern Estonia.

of spiders and crabs lived in coastal waters during the Palaeozoic era, between 541 and 251 million years ago.

They found the ancient creature had a primitive form of compound eye, an optical organ that consists of arrays of tiny visual cells, called ommatidia, similar to those of present-day bees.

Researchers believe their findings suggest compound eyes have changed little over 500 million years.

Professor Euan Clarkson, of the university's school of geosciences, said: 'This exceptional fossil shows us how early animals saw the world around them hundreds of millions of years ago.

'Remarkably, it also reveals that the structure and function of compound eyes has barely changed in half a billion years.'

The right eye of the fossil was partly worn away, giving researchers a clear view inside the organ.

The right eye of the fossil was partly worn away, giving researchers a clear view inside the organ. This image shows a side view of the eye

The remains of the extinct sea creature include an early form of the eye seen in many of today's animals, including crabs, bees and dragonflies. This image shows the full fossil

This revealed details of the eye's structure and function, and how it differs from modern compound eyes.

The species had poor vision compared with many animals today but it could identify predators and obstacles in its path, researchers say.

Its eye consists of approximately 100 ommatidia, which are situated relatively far apart compared to contemporary compounds eyes, the team says.

WHAT ARE TRILOBITES? Trilobites are an extinct group of arthropods, or jointed-legged animals, known from more than 10,000 fossil species. The group Trilobita existed from early in the Cambrian Period, 540 million years ago, until the end of the Permian Period, 250 million years ago. The name Trilobita is derived from the three (tri-) lobed structure of its exterior shell, or exoskeleton. This has a raised central lobe, or axis, and a pair of side lobes, called pleurae. The trilobite body is also divided lengthwise into three regions or tagmata. This includes a head or cephalon, a middle region, or thorax, composed of several to many articulated segments, and a tail plate called a pygidium, which consists of fused segments. Advertisement

Unlike modern compound eyes, the fossil's eye does not have a lens.

This is likely because the primitive species - called Schmidtiellus reetae - lacked parts of the shell needed for lens formation, the team says.

Professor Brigitte Schoenemann, of the University of Cologne, who was involved in the study, said: 'This may be the earliest example of an eye that it is possible to find.

Trilobites are an extinct group of arthropods, or jointed-legged animals, known from more than 10,000 fossil species. This image shows two fossil specimens of the trilobite species Kainops invius, one shown from the side (top) and another from above (bottom)

The group Trilobita existed from early in the Cambrian Period, 540 million years ago, until the end of the Permian Period. This image shows an artist's impression of the Ptychoparia genus of trilobite, found in the Middle Cambrian-aged seabed strata of Eurasia and North America

'Older specimens in sediment layers below this fossil contain only traces of the original animals, which were too soft to be fossilised and have disintegrated over time.'

The team also revealed that only a few million years later, improved compound eyes with higher resolution developed in another trilobite species from the present-day Baltic region.

The full findings of the study were published in the journal Proceedings of the National Academy of Sciences.

It was carried out in collaboration with the University of Cologne and Tallinn University of Technology in Estonia.