The incredible insight into ancient sea creatures drove an evolutionary arms race

According to new research published today, ancient deep-sea creatures called radiodont had an incredible vision that likely led an evolutionary arms race.

The international study, led by Professor John Paterson of the University of New England’s Palaeoscience Research Center, in collaboration with the University of Adelaide, the South Australian Museum and the Natural History Museum (UK), found that radiodont developed sophisticated eyes for over 500 million years ago, with some adapted to the dim light of deep waters.

‘Our study provides new critical information on the evolution of early marine animal ecosystems,’ said Professor Paterson. “In particular, it supports the notion that vision played a crucial role during the Cambrian explosion, a pivotal phase in history where most major groups of animals first appeared during a rapid burst of evolution beyond half a billion years ago “.

Radiodonts, meaning “teeth that radiate”, are a group of arthropods that dominated the oceans some 500 million years ago. The many species share a similar body structure which includes a head with a pair of large segmented appendages for catching prey, a circular mouth with serrated teeth, and a squid-like body. It now seems likely that some lived at depths of up to 1000 meters and developed large, complex eyes to compensate for the lack of light in this extreme environment.

‘When complex visual systems arose, animals could perceive their surroundings better,’ explained Professor Paterson. “This may have fueled an evolutionary arms race between predators and prey. Once established, the vision became a driving force in evolution and helped shape the biodiversity and ecological interactions we see today.”

Some of the earliest radiodont fossils discovered more than a century ago were isolated body parts, and the first attempts at reconstruction led to “Frankenstein’s monsters”.

But in recent decades, many new discoveries – including entire radiodont bodies – have provided a clearer picture of their anatomy, diversity, and possible lifestyles.

The co-author, Associate Professor Diego García-Bellido of the University of Adelaide and the South Australian Museum, said that the rich fossil hoard of Emu Bay Shale on Kangaroo Island in South Australia in particular has contributed to build a clearer picture of the earliest animals on Earth.

“The Emu Bay Shale is the only place in the world that keeps eyes with Cambrian radiodon lenses. The more than thirty specimens of eyes we have now, have shed new light on the ecology, behavior and evolution of these eyes. the largest animals alive. half a billion years ago, “A / Prof. Said García-Bellido.

In 2011, the team published two articles in the journal Nature about the eyes of the 513-million-year-old Emu Bay Shale fossil compounds on Kangaroo Island.

The first paper on this topic documented isolated eye samples up to one centimeter in diameter, but the team was unable to assign them to a known arthropod species. The second article reported the chased eyes of Anomalocaris, a predator up to a meter long, in great detail.

“Our new study identifies the owner of the eyes from our first document from 2011: ‘Anomalocaris’ briggsi – representing a new genus that has yet to be formally named,” said prof. Paterson.

“We have found much larger specimens of these eyes up to four centimeters in diameter that possess a characteristic ‘acute zone’, which is a region of magnified lenses in the center of the eye’s surface that improves light capture and resolution.”

The large lenses of “Anomalocaris” briggsi suggest that it could see in very dim light at depth, similar to the crustaceans of amphipods, a type of shrimp-like creature that exists today. The jagged spines on its appendages filtered out the plankton it detected when looking up.

Dr Greg Edgecombe, a researcher at the Natural History Museum in London and co-author of the study, added that radiodonts from South Australia show that the different feeding strategies previously indicated by the appendices – to capture or filter prey – are paralleled. by differences of the eyes.

“The predator has its eyes attached to its head on the stems, but the filter feeder has them on the surface of the head. The more we learn about these animals, the more diverse their body structure and ecology will be,” said Dr. Edgecombe.

“The new samples also show how the eyes changed as the animal grew. The lenses formed at the edges of the eyes, getting larger and increasing in number in large specimens, just like in many living arthropods. where compound eyes grow has been consistent for over 500 million years. “

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The study “The disparate compound eyes of Cambrian radiodons reveal their evolutionary mode of growth and different visual ecology” was published today in the prestigious journal Scientific advances.

Connection:
https: //doi.org /10.1126 /sciadv.abc6721

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