Ancient Chinese fossils bridge evolutionary gap between periods

New fossils discovered in China hint that complex life evolved millions of years earlier than scientists thought.

 The assemblage suggests that the ancestors of some of today’s animal groups may have arisen before the famed Cambrian explosion.Life on Earth started some time before 3.5 billion years ago, although it was clearly in no rush to become the vast network of diverse beings that exists today, News.Az reports, citing Smithsonian Magazine. 

Traditionally, many scientists suspected that life really took off about 535 million years ago during the Cambrian explosion, an evolutionary event that saw rapid animal diversification and is thought to have brought about many groups that live on in modern times.

However, an unprecedented collection of fossils discovered in China seems to push back the timeline. Researchers describe primitive complex creatures that predate the Cambrian period by millions of years in a study published April 2 in the journal Science.

“We are certainly revealing a more complex picture about the beginnings of the explosion of animal diversity and when that happened,” study co-author Ross Anderson, a paleobiologist at the University of Oxford in England, tells New Scientist’s James Woodford.The transition to the Cambrian period, about 485.4 million to 538 million years ago, from the preceding Ediacaran period, roughly 538 million to 635 million years ago, has remained mysterious. Scientists have wondered whether the Cambrian explosion was truly bursting with evolution or if the complex creatures of that time had older roots. Previously found Ediacaran fossils, however, showed animals with strange body plans that didn’t resemble Cambrian creatures or those alive today.

The newly discovered trove of fossils, unearthed in southwest China, might finally provide the sought-after bridge between the time frames. The more than 700 fossils, dated to between 539 million and 554 million years ago, include organisms that resemble beings from both the Cambrian and Ediacaran, creatures previously only known to exist during the Cambrian explosion and animals that have never been described.“Our discovery closes a major gap in the earliest phases of animal diversification,” study co-author Gaorong Li, a paleobiologist at Yunnan University in China, says in a statement. “For the first time, we demonstrate that many complex animals, normally only found in the Cambrian, were present in the Ediacaran period, meaning that they evolved much earlier than previously demonstrated by fossil evidence.” 

The most common creature, at 185 recovered specimens, was a worm-like animal roughly the size of an adult’s index finger with a disk that kept it anchored to the ocean floor. This organism and some of the others were bilaterians, which have two mirrored sides, an important adaptation that helped early animals travel in sediment and up and down in water, develop a nervous system and eventually take over the animal kingdom, study co-author Frankie Dunn, a paleontologist at the Oxford University Museum of Natural History, tells Scientific American’s Jackie Flynn Mogensen. Most modern-day animals, including humans, are bilaterians, and researchers previously thought they mostly arose during the Cambrian.What’s more, the researchers uncovered fossils of what appear to be the earliest known deuterostomes, a broad group of animals that currently includes all vertebrates. One of them was a U-shaped creature tethered to the seafloor that looks like a type of extinct Cambrian creature related to living sea stars and acorn worms.

The overall discovery “makes a huge amount of sense,” says Emily Mitchell, a paleontologist at the University of Cambridge in England, who wasn’t involved in the study, to the Associated Press’ Seth Borenstein. “Because the Ediacaran contains animals, we know there must have been a transitional stage between them and the Cambrian fauna. But until now, we didn’t really have any evidence of this.”

News.Az 

By Leyla Şirinova