Early animals engineered first mass extinction: Study

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Researchers have discovered new fossil evidence to prove that the world’s first mass extinction 540 million years ago was caused by metazoans — the earth’s early animals — also called “ecosystem engineers.”

The metazoans which were newly evolved biological organisms, altered the environment radically to drive older species Ediacaran to extinction.

These metazoans comprise most common forms of life today including vertebrates and arthropods, molluscs, annelids, sponges and jellyfish.

“These new species were ‘ecological engineers’ who changed the environment in ways that made it more and more difficult for the Ediacarans to survive,” said Simon Darroch, Assistant Professor at the Vanderbilt University in Tennessee, US.

The effects of the diversification and spread of animals across the globe, known as Cambrian explosion, may have also led to the extinction of the Earth’s first multicellular organisms, known as Ediacarans, the researchers said.

The Ediacarans were a largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses. They spread around the globe about 600 million years ago.

The team also found one of the best preserved examples of a mixed community of Ediacarans and animals, which provides the best evidence of a close ecological association between the two groups.

“Until this, the evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms was limited,” Darroch added.

The study describes new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans and vertically oriented metazoan trace fossils.

“Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period,” Darroch said.

The discovery of some new fossil sites that preserved both Ediacara biota and animal fossils (both animal burrows — “trace fossils” — and the remains of animals themselves) which shared the same communities, has allowed speculation about how these two very different groups of organisms interacted.

Some of the burrow fossils found are usually interpreted as being formed by sea anemones, which are passive predators that may have preyed upon Ediacaran larvae.

Further, stands of Ediacaran frondose organisms, with animal fossils preserved in place coiled around their bases were also found.

“These new fossil sites reveal a snapshot of a very unusual ‘transitional’ ecosystem existing right before the Cambrian explosion, with the last of the Ediacara biota clinging on for grim death, just as modern-looking animals are diversifying and starting to realise their potential,” Darroch explained.

“There is a powerful analogy between the Earth’s first mass extinction and what is happening today,” he said, adding, “the end-Ediacaran extinction shows that the evolution of new behaviours can fundamentally change the entire planet, and today we humans are the most powerful ‘ecosystems engineers’ ever known.”

The findings were published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.


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