The 500 million year old evolutionary arms race for better vision

A new study suggests that a half-billion-year-old “evolutionary arms race” may have been sparked by advances in the vision of deep-sea giants called “radiodonts.” The “Cambrian Explosion” took place about 541 million years ago and lasted about 13-25 million years. This is the beginning of the evolutionary arms race when almost all major animal groups emerged. Now, a new study claims to provide “critical new information” about the evolution of the earliest marine ecosystems emerging at the time, leading to better predators characterized by improved visibility.

Extreme environments formed the evolutionary arms race

The new study is published in Sciences progress . The study was written by Professor John Paterson of the University of New England Palaeoscience Research Center , in collaboration with the University of Adelaide , the South Australian Museum and the Natural History Museum in London. Speak with Archeology News Network Professor Paterson says the study shows how “vision” played a crucial role in the Cambrian explosion more than half a billion years ago.

Radiodonts are named for their “radiating teeth,” and about 500 million years ago, their muscular, overlapping ventral flaps propelled these creatures through the oceans, similar to the way modern rays and squid swim. Radiodont’s heads had a pair of large “segmented appendages for catching prey,” and their round mouths were lined with rows of serrated teeth. The new study suggests that some of these animals inhabited ocean layers that were 1,000 meters (3,280 feet) deep. And they developed “large, complex eyes” to make up for the lack of light in this extremely deep water environment.

The radiodont Anomalocaris, with its large, pediculated eyes, is believed to be a leading marine predator that swam in the oceans more than 500 million years ago.  (Katrina Kenny / University of New England)

The radiodont Anomalocaris, with its large, stalked eyes, is believed to be a leading marine predator that swam in the oceans more than 500 million years ago. (Katrina Kenny / University of New England )

Better visibility was an important evolutionary driver

The study was largely based on fossils recovered from the Emu Bay Shale formation on Kangaroo Island in South Australia. The paper’s co-author, Associate Professor Diego García-Bellido of the University of Adelaide and the South Australian Museum, said Emu Bay Shale is “the only place in the world that preserves eyes with Cambrian radiodontic lenses.”

The study concluded that when more complex visual systems emerged, animals became more aware of their environment. This triggered an “evolutionary arms race” between predators and prey, according to the study. In essence, vision became “a driving force in evolution” shaping the biodiversity and ecological interactions we see today.

Fossil Eyes: A Decade of Evolutionary Progress and Insights

The same research team published two articles in the journal Nature in 2011 after studying a pair of one centimeter diameter ‘fossilized compound eyes’ discovered on Kangaroo Island.

At the time, however, the creature to whom these eyes belonged was unclear, but now it has been perfectly portrayed and the creature has been named ‘ Anomalocaris’ briggsi. Professor Paterson said they found much larger copies of these eyes that had distinctive ‘acute zones’.

These “acute zones” are located in the lens of the eye and serve to amplify the amount of light entering the eye and to sharpen the resolution. And that’s why the researchers think ‘Anomalocaris’ briggsi could see in very dim light, at great depths underwater.

Dr. Greg Edgecombe, a researcher at The Natural History Museum and a co-author of the new study, says the 2011 study found South Australian radiodonts had different “feeding strategies” for capturing or filtering prey, which were indicated by the appendages. However, it is now known that the predators had eyes on these appendages on the surface of the head, “on stems,” said Dr. Edgecombe.

The eye of 'Anomalocaris' briggsi.  Left: the complete fossil eye (the scale bar is 5 mm or 0.2 inch);  Center: close-up of lenses (the scale bar is 5 mm or 0.2 inch);  Right: a reconstruction of an artist who uses the

The eye of ‘Anomalocaris’ briggsi. Left: the complete fossil eye (the scale bar is 5 mm or 0.2 inch); Center: close-up of lenses (the scale bar is 5 mm or 0.2 inch); Right: An artist’s reconstruction showing the “acute zone” of enlarged lenses, allowing the creature to see in dim light. (J. Paterson / University of New England )

Fossil traces of the 500 million year old Cambrian explosion

The new study shows how radiodonts’ eyes grew and evolved as the species evolved and got bigger, and how the eye lenses formed at the rim of the eyes. In addition, the eyes were found to enlarge significantly in large specimens, as noted in many modern arthropods. And this is how compound eyes have grown for more than 500 million years, according to the scientists’ study.

It should be added that the eye fossils examined in this new study are among the oldest ever discovered. In 2017 The BBC wrote of the discovery of an “exceptionally 530 million year old well-preserved trilobite fossil with” the oldest eye ever discovered “, which can be seen in many of today’s animals, including crabs, bees and dragonflies. And it was during this time too.” Cambrian explosion “that radiodonts emerged, and therefore their fossils represent the” birth of the predator “on planet Earth.

Top image: An artist’s reconstruction of ‘Anomalocaris’ briggsi, the deep-sea creature that started an evolutionary arms race because its improved vision made it a better predator. Source: Katrina Kenny / University of New England

By Ashley Cowie

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