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December 6th, 2020 
Awake Goy A new study suggests a half-billion-year-old “evolutionary arms race” might have been sparked by developments in the vision of deep-sea giants called “radiodonts.” The “Cambrian explosion” occurred approximately 541 million years ago and lasted for about 13-25 million years. This is the beginning of the evolutionary arms race when nearly all major animal groups emerged. Now, a new study claims to provide “critical new information” about the evolution of the earliest marine animal ecosystems that emerged at this time, leading to better predators characterized by enhanced vision.
Extreme Environments Shaped Evolutionary Arms Race
The new study is published in Sciences Advances . The study was written by Professor John Paterson from the University of New England’s Palaeoscience Research Centre , in collaboration with the University of Adelaide , the South Australian Museum and the Natural History Museum in London. Speaking with Archaeology News Network , Professor Paterson says the study highlights how “vision” played a crucial role during the Cambrian Explosion over half a billion years ago.
Radiodonts are named after their ”radiating teeth” and around 500 million years ago their muscular, overlapping ventral flaps propelled these creatures through the oceans, similar to the ways modern rays and cuttlefish swim. Radiodonts’ heads boasted a pair of large “segmented appendages for capturing prey” and their circular mouths were fringed with rows of serrated teeth. The new study suggests some of these animals inhabited ocean layers that were 1000 meters (3280 feet) deep. And they developed “large, complex eyes” to compensate for the lack of light in this extreme deep-water environment.
The radiodont Anomalocaris, with its large, stalked eyes, is considered to be a leading marine predator that swam in the oceans over 500 million years ago. (Katrina Kenny / University of New England )
Better Vision Was A Major Evolutionary Driving Force
The study was largely based on fossils recovered from the Emu Bay Shale formation on South Australia’s Kangaroo Island . The paper’s co-author, Associate Professor Diego García-Bellido from the University of Adelaide and the South Australian Museum, said Emu Bay Shale is “the only place in the world that preserves eyes with lenses of Cambrian radiodonts.”
The study concluded that when more complex visual systems arose animals gained an increased awareness of their surroundings. This, according to the study, caused an “evolutionary arms race” between predators and prey. Essentially, 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 papers in the journal Nature in 2011 after they studied a pair of “one centimeter diameter, fossilized compound eyes” that were discovered on Kangaroo Island.
However, at that time the creature to whom these eyes belonged was unclear, but now, it has been brought into perfect focus and the creature has been named ‘ Anomalocaris’ briggsi. Professor Paterson said they found much larger specimens of these eyes that possessed distinctive “acute zones.”
Sitting in the lens of the eye, these “acute zones” serve to enhance the amount of light entering the eye, and to sharpen resolution. And this is why the researchers think ‘Anomalocaris’ briggsi could see in very dim light, at great underwater depths.
Dr Greg Edgecombe, a researcher at The Natural History Museum and a co-author of the new study, says the 2011 study determined South Australian radiodonts had different “feeding strategies” for capturing or filtering prey, that were indicated by the appendages. However, now it is known that the predators had eyes attached to these appendages on the surface of the head, “on stalks,” Dr Edgecombe said.
The eye of ‘Anomalocaris’ briggsi. Left: The complete fossil eye (the scale bar is 5mm or 0.2 inches); Middle: close-up of lenses (the scale bar is 5mm or 0.2 inches); 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 From The 500-Million-Year-Old Cambrian Explosion
The new study shows how radiodonts’ eyes grew and developed as the species evolved and became bigger, and how the eye lenses formed at the margin of the eyes. Furthermore, the eyes were found to grow significantly bigger in large specimens, just as is noted in many modern arthropods. And this is the way 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 about the discovery of an “exceptional 530-million-year-old well-preserved trilobite fossil with “the oldest eye ever discovered,” that is seen in many of today’s animals, including crabs, bees and dragonflies. And it was also during this “Cambrian explosion” that radiodonts emerged, and this is why 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 enhanced vision made it a better predator. Source: Katrina Kenny / University of New England
By Ashley Cowie
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