A team of paleontologists from Australia and the United Kingdom has discovered that ancient deep-sea creatures called radiodonts developed refined eyes more than 500 million years ago (Cambrian period), some of which were specially adapted to the weak light of deep water.
An artist’s reconstruction of ‘Anomalocaris’ briggsi. Image credit: Katrina Kenny.
Radiodonts (meaning ‘radiating teeth’) are a group of arthropods that dominated the oceans about 500 million years ago.
The many Radiodont species share a similar body layout, consisting of a head with a pair of large, segmented appendages for catching prey, a round mouth with serrated teeth, and a squid-like body.
It now seems likely that some lived at depths up to 1,000 m (3,281 feet) and had developed large, complex eyes to make up for the lack of light in this extreme environment.
“As complex visual systems evolved, animals could better sense their environment, possibly sparking an evolutionary arms race between predators and prey,” said lead author Professor John Paterson, a researcher at the Palaeoscience Research Center at the University of New England.
“Once established, vision became a driving force behind evolution and helped shape the biodiversity and ecological interactions we see today.”
In 2011, Professor Paterson and colleagues documented isolated eye samples up to 1 cm (0.4 in) in diameter from the 515 million-year-old Emu Bay Shale on Kangaroo Island, but were unable to assign them to a known arthropod species. .
They also described the pedicled eyes of it Anomalocaris, an apex predator up to 1 m long, in great detail.
“The Emu Bay Shale is the only place in the world where eyes are preserved with Cambrian radiodont lenses,” says Dr. Diego García-Bellido, a researcher in the School of Biological Sciences at the University of Adelaide and the South Australian Museum.
“The more than 30 specimens of the eyes that we have today have shed new light on the ecology, behavior and evolution of these, the largest animals that lived 500 million years ago.”
Acute zone-like eyes from ‘Anomalocaris’ briggsi. Image credit: John Paterson, University of New England.
In the new study, the researchers identified the owner of 515 million year old eye samples: ‘Anomalocaris’ briggsi, which represents a new gender that has yet to be formally named.
“We have discovered much larger specimens of these eyes up to 4 cm (1.6 in) in diameter that have a distinctive ‘acute zone’, an area of enlarged lenses in the center of the ocular surface that improves light absorption and resolution , ‘Said Professor Paterson.
The big lenses of ‘Anomalocaris’ briggsi suggest it could see at depth in very dim light, similar to amphipods, a type of shrimp-like creature that exists today.
The strips of spines on the appendages filtered plankton it discovered by looking up.
“These specimens showed us that the feeding strategies of the animals previously indicated by the appendages – for capturing or filtering prey – are associated with differences in the eyes,” said Dr. Greg Edgecombe, a paleontologist in the Earth Sciences Department at the Natural History Museum, London.
“The predatory radiodont in our samples has the eyes attached to the head to stems, but one that has filter feeders has them on the surface of the head.”
“The more we learn about these animals, the more diverse their body plan and ecology turns out to be.”
“The new samples also show how the eyes changed as the animal grew. The lenses formed on the edge of the eyes, enlarging and increasing in number in large specimens – as in many living arthropods. The way compound eyes grow has been consistent for over 500 million years. “
The scientists also found that the Anomalocaris eyes described in 2011 are probably of a kind called Anomalocaris aff. canadensis.
“The Australian material is unique among dozens of radiodontic cases around the world in the Cambrian period, as it is the only place where the visual surface of the eye is preserved,” said Dr. Edgecombe.
“In other locations in China, Canada, the United States and elsewhere, only the outline of the eyes is known, but there is no information about their lenses.”
The study has been published in the journal Sciences progress.
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John R. Paterson et al. 2020. Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology. Science Advances 6 (49): eabc6721; doi: 10.1126 / sciadv.abc6721
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