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New fossils reshuffle the evolutionary tree

Education

THE discovery of well-preserved marine creatures that lived 500 million years ago in the region of South Australia is shedding new light on the ancient ancestors of humans and other vertebrates. 

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While fossils of the blind water creatures known as vetulicolians had been found at other sites across the world, the study to be published in BMC Evolutionary Biology describes a new species Nesonektris found at Emu Bay, Kangaroo Island.

The revised place for Nesonektris and other vetulicolians on the evolutionary tree is thanks to the unique preservation characteristics of the Kangaroo Island fossil site, meaning that anatomical features could be properly identified for the first time.

These ancient water creatures are among our distant cousins.

“A straight narrow structure at the centre of vetulicolian fossils from other sites had always been assumed to be a gut,” explained lead author of the paper, Dr Diego Garcia-Bellido, Australian Research Centre Future Fellow with the University of Adelaide’s Environment Institute.

“The fossils we’ve studied from Emu Bay show that this structure is actually like a notochord, a precursor to a backbone,” he said.  “It would have been made of cartilage originally.”

Rapid mineralisation of the notochord structure – probably following an ancient mudslide at the site – protected it from degradation.

Prior anatomical ambiguities in descriptions of vetulicolians meant that the place of these sea creatures in evolution had remained controversial since their initial description in 1911.

“We believe our study places vetulicolians higher up in the evolutionary tree than was initially thought,” said Dr Garcia-Bellido.

“Now we think these creatures belong with other vertebrate relatives like tunicates,” he said. “These ancient water creatures are among our distant cousins.”

The Emu Bay fossil site is well known for preservation of soft tissues.

In 2011 Dr Garcia-Bellido was amongst scientists reporting on exceptionally well-preserved fossilised eyes in an ancient arthropod.

The discovery placed complex compound eyes around 85 million years earlier than they had previously been believed to exist.  

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