The ancient “Radiating Teeth” destroyed an incredible visionary evolutionary arms race in deep sea creatures

Reconstruction of the ‘Anomalocaris’ briggsi artist floating in the twilight zone. Credit: Katrina Kenny

Ancient marine creatures called radiodonts had an incredible ability to see, which led to an evolutionary arms race, according to a new study published on December 2, 2020.

An international study led by Professor John Paterson of the University of New England’s Paleocene Research Center, in collaboration with the University of Adelaide, the Museum of South Australia and the Museum of Natural History (UK), found that radionuclides evolved over 500 million years. previously, some were adapted to the faint light of deep water.

“Our research provides critically new information about the evolution of the first marine ecosystems,” said Professor Paterson. “In particular, it supports the view that vision played a crucial role during the Cambrian Explosion, when very important groups of animals formed during the rapid evolutionary explosion of the first half billion years ago, a key stage in history.”

Radiodonts, meaning “radiant teeth,” are a group of arthropods that dominated the oceans about 500 million years ago. Many species share a body shape similar to that of a head with a pair of large, segmented appendages to catch prey, a round mouth with serrated teeth, and a squid-like body. It now appears that some live at depths of up to 1,000 meters and have developed large, complex eyes to compensate for the lack of light in this extreme environment.

Anomalocaris Briggsi's eye

‘Anomalocaris’ Briggsi’s eye. Left full fossil eye (scales rod is 5 mm); average proximity of the lens (scale bar is 0.5 mm); the reconstruction of the right artist showing the sharp region. Credit: University of Adelaide

“When complex visual systems emerged, animals were able to feel their surroundings better,” explained Professor Paterson. “This could lead to an evolutionary arms race between predators and predators. Vision has been the driving force behind evolution since its inception, and has helped shape the biodiversity and ecological interactions we see today. ”

Some of the first radiodont fossils discovered a century ago were isolated from body parts, and attempts to reconstruct them resulted in “Frankenstein monsters.”

However, many new discoveries over the past few decades – including all radionuclide objects – have provided a clearer picture of their anatomy, diversity, and possible lifestyles.

Radiodont Anomalocaris

The radionuclide Anomalocaris, with its large stalked eyes, is the largest predator floating in the oceans 500 million years ago. Credit: Katrina Kenny

The co-author, Diego García-Bellido, an associate professor at the University of Adelaide and the Museum of South Australia, said the rich treasure trove of Emu Gulf Shale on Kangaroo Island in South Australia helped create a clearer picture of the world’s earliest animals.

“The Emu Gulf Shale is the only place in the world that protects the eyes with the lenses of Cambrian radiodontists. The more than thirty eye samples we have today shed new light on their ecology, behavior and evolution, the largest animals that lived half a billion years ago, “said A / Prof. García-Bellido.

In 2011, the group published two documents in Nature magazine about fossilized mixed eyes from the 513-million-year-old Emu Bay Sheila on Kangaroo Island.

The first document on this subject documented isolated eye specimens up to one centimeter in diameter, but the group was unable to identify them as a known arthropod species. The second paper described in great detail the pinned eyes of Anomalocaris, the largest predator up to one meter long.

“Our new study identified the owner of the eye from our first 2011 document: ‘Anomalocaris’ briggsi – represents a new species that has not yet been officially named,” he said.

“We found larger specimens of these eyes, up to four centimeters long, with an enlarged lens area in the center of the eye surface and a distinct ‘sharp zone’ that increased light retention.”

The large lenses of the ‘Anomalocaris’ briggsi show that they can see in very dim light at a depth similar to that of an amphibian crustacean, a living species resembling a shrimp that exists today. The curly pieces in the appendages looked up and filtered the plankton.

Researcher at the Museum of Natural History in London and co-author of the study, Dr. Greg Edgecombe added that the different feeding strategies shown by South Australian radiodontists in advance of supplements – either to catch or filter – are parallel to the differences. in the eyes.

“In the predator, the eyes are glued to the head on the branches, but the filter is on the surface of the feeder’s head. The more we learn about these animals, the more different their body plans and ecology, ”said Dr. Edgecombe.

“New examples also show how the eyes change as the animal grows. The lenses that form at the edge of the eye grow larger and multiply in large specimens – as in many living arthropods. The process of growing mixed eyes has been going on for more than 500 million years. ”

Reference: “Different mixed eyes of Cambrian radiodontists reveal their developmental growth and different visual ecology” John R. Paterson, Gregory D. Edgecombe and Diego C. García-Bellido, 2 December 2020, Scientific developments.
DOI: 10.1126 / sciadv.abc6721

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