New three-dimensional reconstructions display how some of the world’s earliest animals developed, and offer some answers as to why they went extinct.
A strange group of uniquely shaped organisms known as rangeomorphs may have been some of the earliest animals to appear on Earth, they were uniquely suited to ocean conditions 575 million years ago. A new model created by researchers at the University of Cambridge has resolved many of mysteries around the structure, evolution and extinction of these ‘proto animals’. The findings are reported today in the journal PNAS.
Rangeomorphs were among the earliest large organisms to grace the Earth, existing during a period where most other forms of life were microscopic in size. Most rangeomorphs were approximately 10 centimeters high, although some managed to grow to a height of two meters.
These animals were ocean dwellers and lived during the Ediacaran period, between 635 and 541 million years ago. Their bodies comprised of soft branches, each with many smaller side branches, forming a geometric shape known as a fractal, which can be seen as many familiar branching shapes such as fern leaves and even river networks.
Rangemorphs were unlike any modern organism seen today, which has made it difficult to determine how they completed tasks such as feeding, growing or reproducing. This has therefore made it difficult to link them to any particular modern group. However, despite the fact that they looked like plants, evidence suggests that rangeomorphs were actually some of the earliest animals.
“We know that rangeomorphs lived too deep in the ocean for them to get their energy through photosynthesis as plants do,” said Dr. Jennifer Hoyal Cuthill of Cambridge’s Department of Earth Sciences, who led the research. “It’s more likely that they absorbed nutrients directly from the sea water through the surface of their body. It would be difficult in the modern world for such large animals to survive only on dissolved nutrients.”
“The oceans during the Ediacaran period were more like a weak soup – full of nutrients such as organic carbon, whereas today suspended food particles are swiftly harvested by a myriad of animals,” said co-author Professor Simon Conway Morris.
Starting 541 million years ago, the conditions in the oceans with the start of the Cambrian Explosion – a period of rapid evolution when most major animal groups first emerge in the fossil record and competition for nutrients increased dramatically.
Rangeomorphs have often been considered a ‘failed experiment’ of evolution as they died out so quickly after the Cambrian Explosion began in earnest, but this new analysis shows how successful they once were.
Rangeomorphs almost completely filled the space surrounding them, with a large total surface area. This enabled them to be very efficient feeders with the ability to extract the maximum amount of nutrients from the ocean water.
“These creatures were remarkably well-adapted to their environment, as the oceans at the time were high in nutrients and low in competition,” said Dr Hoyal Cuthill. “Mathematically speaking, they filled their space in a nearly perfect way.”
Dr. Hoyal Cuthill examined rangeomorph fossils from a number of locations across the world, and used them to make the very first computer reconstructions of the development and three-dimensional structure of these organisms, showing how they were actually well-suited to their Ediacaran environment.
As the Cambrian Explosion began however, the rangeomorphs became ‘sitting ducks’, as they had no defensive features to protect them from predators, which were beginning to evolve, and the changing chemical composition of the ocean meant that they could no longer get the nutrients they required to feed.
“As the Cambrian began, these Ediacaran specialists could no longer survive, and nothing quite like them has been seen again,” said Dr Hoyal Cuthill.
Contributing Source: University of Cambridge
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