Friday, 4 December 2020

Evolution News - Arms Races and the Evolution of Vision

An artist’s reconstruction of ‘Anomalocaris’ briggsi swimming within the twilight zone.

Image: Katrina Kenny
Incredible vision in ancient marine creatures drove an evolutionary arms race | Newsroom | University of Adelaide

One of the abilities that gave the Cambrian biota such a big advantage over the earlier sedentary Ediacaran organisms that they probably exterminated them, was the ability to move.

The next major development was the ability to detect movement with vision. This in turn led to an evolutionary arms race that hugely added to the biodiversity in the biota of the early Earth. The evolutionary advantage in being able to detect prey species, and the evolutionary pressure this placed on their prey to see and avoid predators, led to an evolutionary arms race and a period of very rapid diversification, accounting, in part, for the rapid appearance over some 60 million years of the so-called Cambrian Explosion.

Our study provides critical new information about the evolution of the earliest marine animal ecosystems. In particular, it supports the idea that vision played a crucial role during the Cambrian Explosion, a pivotal phase in history when most major animal groups first appeared during a rapid burst of evolution over half a billion years ago.

Professor John Paterson, lead author
Palaeoscience Research Centre
University of New England
This is the conclusion of a international group of scientists, led by Professor John Paterson from the University of New England’s Palaeoscience Research Centre, and including scientists from the University of Adelaide, the South Australian Museum and The Natural History Museum (UK).

According to their research, the first organisms to evolve vision were a group known as the radiodonts, which included Anomalocaris. This group developed sophisticated eyes over 500 million years ago, enabling them to hunt in the dim light of deep water, giving them access to the many bottom-feeding organisms. The huge jaws of Anomalocaris were first thought to be a separate species because, being hard, they tended to fossilise comparatively easily compared to the rest of the soft-bodied organism.

Acute zone–type eye of ‘A.’ briggsi.

(A to C) SAM P54853; inset in (A) shows the position of (B), and inset in (B) shows the position of (C); arrowheads in (A) indicate contact between eye sclerite and visual surface. (D) SAM P57421. (E and F) SAM P48377a,b, part (E) and counterpart (F). Scale bars, 5 mm (A and D to F), 1 mm (B), and 0.5 mm (C). es, eye sclerite; mr, marginal rim.

Photo credit: J. Paterson, University of New England (A to F).

Acute zone–type eye of ‘A.’ briggsi.

(A to D) SAM P54248. (E and F) SAM P52901a,b, part (E) and counterpart (F). (G) SAM P55428. Scale bars, 5 mm (A), 3 mm (B and E to G), 2 mm (C), and 1 mm (D). es, eye sclerite; mr, marginal rim.
Photo credit: J. Paterson, University of New England (A to G).

Compound eye of A. aff. canadensis.

(A and B) SAM P49070; inset in (A) shows the position of (B). (C) SAM P52893. Scale bars, 5 mm (A and C) and 1 mm (B).
Photo credit: J. Paterson, University of New England (A to C).

Head reconstructions of Emu Bay Shale radiodonts, with the visual surface of the eyes shown in gray.

(A and B) ‘A.’ briggsi showing sessile (nonstalked) eyes in lateral and anterior views, respectively, with the acute zone depicted by lighter shading; the dorsal head sclerite and oral cone are conjectural. (C and D) A. aff. canadensis showing stalked eyes in lateral and anterior views, respectively; the position and orientation of the eyes and the presence of a dorsal head sclerite are based on specimens of A. canadensis from the Burgess Shale and Anomalocaris saron from the Chengjiang biota, in addition to the eye pair from the Emu Bay Shale.
The University of Adelaide press release anouncing the findings explains:
Radiodonts, meaning “radiating teeth”, are a group of arthropods that dominated the oceans around 500 million years ago. The many species share a similar body layout comprising of a head with a pair of large, segmented appendages for capturing prey, a circular mouth with serrated teeth, and a squid-like body. It now seems likely that some lived at depths down to 1000 metres and had developed large, complex eyes to compensate for the lack of light in this extreme environment.

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

Some of the first radiodont fossils discovered over a century ago were isolated body parts, and initial attempts at reconstructions resulted in “Frankenstein’s monsters”.

But over the past few decades many new discoveries — including whole radiodont bodies — have given a clearer picture of their anatomy, diversity and possible lifestyles.

Co-author, Associate Professor Diego García-Bellido from the University of Adelaide and South Australian Museum, said the rich treasure trove of fossils at Emu Bay Shale on South Australia’s Kangaroo Island in particular has helped to build a clearer picture of Earth’s earliest animals.

“The Emu Bay Shale is the only place in the world that preserves eyes with lenses of Cambrian radiodonts. The more than thirty specimens of eyes we now have, has shed new light on the ecology, behaviour and evolution of these, the largest animals alive half-a-billion years ago,” A/Prof. García-Bellido said.
The team had earlier, in 2011, found fossils of a large sophisticated compound eye, 1 cm in diameter, but were unable then to identify assign it to a particular species. They have now found larger specimens, up to 4 cm in diameter and have identified the owner as a new, so far unnamed species they have called A. briggsii.
Our new study identifies the owner of the eyes from our first 2011 paper: ‘Anomalocaris’ briggsi — representing a new genus that is yet to be formally named,” Prof. Paterson said.

“We discovered much larger specimens of these eyes of up to four centimetres in diameter that possess a distinctive ‘acute zone’, which is a region of enlarged lenses in the centre of the eye’s surface that enhances light capture and resolution.”

The large lenses of ‘Anomalocaris’ briggsi suggest that it could see in very dim light at depth, similar to amphipod crustaceans, a type of prawn-like creature that exists today. The frilly spines on its appendages filtered plankton that it detected by looking upwards.

Dr Greg Edgecombe, a researcher at The Natural History Museum, London and co-author of the study, added that the South Australian radiodonts show the different feeding strategies previously indicated by the appendages – either for capturing or filtering prey – are paralleled by differences in the eyes.

“The predator has the eyes attached to the head on stalks but the filter feeder has them at the surface of the head. The more we learn about these animals the more diverse their body plan and ecology is turning out to be,” Dr Edgecombe said.

“The new samples also show how the eyes changed as the animal grew. The lenses formed at the margin of the eyes, growing bigger and increasing in numbers in large specimens – just as in many living arthropods. The way compound eyes grow has been consistent for more than 500 million years.”
The groups finding were published open access, a couple of days ago, in Science Advances:


Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic marine ecosystems, but information on their vision is limited. Optical details exist only in one species from the Cambrian Emu Bay Shale of Australia, here assigned to Anomalocaris aff. canadensis. We identify another type of radiodont compound eye from this deposit, belonging to ‘Anomalocaris’ briggsi. This ≤4-cm sessile eye has >13,000 lenses and a dorsally oriented acute zone. In both taxa, lenses were added marginally and increased in size and number throughout development, as in many crown-group euarthropods. Both species’ eyes conform to their inferred lifestyles: The macrophagous predator A. aff. canadensis has acute stalked eyes (>24,000 lenses each) adapted for hunting in well-lit waters, whereas the suspension-feeding ‘A.’ briggsi could detect plankton in dim down-welling light. Radiodont eyes further demonstrate the group’s anatomical and ecological diversity and reinforce the crucial role of vision in early animal ecosystems.

Paterson, John R.; Edgecombe, Gregory D.; García-Bellido, Diego C.
Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology
Science Advances 02 Dec 2020: Vol. 6, no. 49, eabc6721; DOI: 10.1126/sciadv.abc6721

Copyright: © 2020 The authors. Published by The American Association for the Advancement of Science.
Open access. Reprinted under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Creationists who have been fooled into thinking the TOE is somehow a theory in crisis and about to be overthrown by the Bible-literalist, fundamentalist Intelligent [sic] Design superstition, might like to read the press release and the paper in Science Advances to try to detect signs of this 'crisis', since normal people might read it and see how evolution is the rational explanation for the biodiversity this paper explains. Nowhere is there reference to magic or the intervention of magic creative entities, intelligent or otherwise. This is also true of every other scientific paper ever published.

Having found the courage to do so, they might like then to question why they have been duped by people who need to misrepresent science and mislead their followers.

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