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In Ediacaran Seas, Huge Rangeomorphs Appeared with a “Bang”


At first glance this sounds like a variation on theories that attribute the burst of diversification associated with the Cambrian explosion not to intelligent design – God forbid – but to changes in the chemical composition of the early ocean.

Simon Conway Morris and his Cambridge University colleague Jennifer Hoyal Cuthill were curious about the sudden appearance of towering rangeomorphs, odd organisms of the Ediacaran period that preceded the Cambrian. At a time when other organisms were very small, these frond-like animals (maybe, or perhaps plants, no one really knows) could reach heights up to two meters.

Dr. Hoyal Cuthill’s way of describing their sudden appearance about 571 million years ago is striking: “They show up in the fossil record with a bang, at very large size.” They attribute this “bang” to changes in “ocean chemistry.”

From Science Daily:

The researchers used micro-CT scanning, photographic measurements and mathematical and computer models to examine rangeomorph fossils from south-eastern Newfoundland, Canada, the UK and Australia.

Their analysis shows the earliest evidence for nutrient-dependent growth in the fossil record. All organisms need nutrients to survive and grow, but nutrients can also dictate body size and shape. This is known as ‘ecophenotypic plasticity.’ Hoyal Cuthill and her co-author Professor Simon Conway Morris suggest that rangeomorphs not only show a strong degree of ecophenotypic plasticity, but that this provided a crucial advantage in a dramatically changing world. For example, rangeomorphs could rapidly “shape-shift,” growing into a long, tapered shape if the seawater above them happened to have elevated levels of oxygen.

“During the Ediacaran, there seem to have been major changes in Earth’s oceans, which may have triggered growth, so that life on Earth suddenly starts getting much bigger,” said Hoyal Cuthill. “It’s probably too early to conclude exactly which geochemical changes in the Ediacaran oceans were responsible for the shift to large body sizes, but there are strong contenders, especially increased oxygen, which animals need for respiration.”

They report this in Nature Ecology and Evolution, “Nutrient-dependent growth underpinned the Ediacaran transition to large body size.”

Yes, this is very much like the “oxygen theory” of the Cambrian explosion. Big “bangs” in diversity may require shifts in ocean chemistry. “Bangs” in the size of organisms may require changes in available nutrients, including oxygen. But building new animals, or new plants, major leaps and novelties in biology, cannot dispense with the need for new biological information.

Anything that Simon Conway Morris puts his name on is of immediate interest, but this would seem to evade the most fascinating question of all in life’s history: the information enigma. For more on that, see our concise documentary of the same name, highlighting the work of Stephen Meyer and Doug Axe:

“All organisms need nutrients to survive and grow,” as they blandly assert, and that is obviously the case. But without infusions of information, which happen with a suddenness that is also a signature of the capacity for invention that we know from our own human experience, there would be no organisms at all, small or large.

Image credit: Rangeomorphs, by Jennifer Hoyal Cuthill.