Paleontologists discovered 700 fossils of small, soft-bodied animals that lived between 546 and 539 million years ago during the Ediacaran period, showing a major change in animal life as it occurred. Many of them are strange and do not appear to be animals to the untrained eye.
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The fossils, found in China’s Yunnan Province, are collectively known as the Jiangchuan Biota. They are in a form called carbonaceous film, a dark, two-dimensional layer of carbon that remains after an organism has been compressed during fossilization. This preserved anatomical details such as the intestine as well as feeding and locomotion patterns.
The discovery is very important because it shows the rapid diversity of animal life already taking place during the Ediacaran period, before the well-known evolutionary process that took place in the following Cambrian period. By the end of this Cambrian Period, the first members of many animal groups that live today had appeared.
During the Ediacaran period, the Earth was a very different place than it is today. The Earth was emerging from a deep ice core called Snowball Earth, the continents were at very different positions, and atmospheric oxygen levels were very low.
Among all these, the first animal life appeared in the seas. The oldest known animal fossils are from about 574 million years ago, with creatures that resemble fern leaves or feathers. Other previously known Ediacaran fauna included sponges and cnidarians, jellyfish and corals.
“If you were to look back at the Cambrian, you would be able to perceive the vastness of the animal life around you, but not so in the Ediacaran period, where the recognizable animals might have been few and far between.
Among the remains of the Jiangchuan Biota, researchers discovered the oldest known members of a broad group called deuterostomes. That’s notable because organisms – including humans – are deuterostomes, although they are more diverse than those that live in the Ediacaran seas.
The fossils of the Jiangchuan Biota included amphipods, whose bodies can be divided into equal parts. Most animals today are bipedal but that was a change during the Ediacaran period.
The fossils included animals with a U-shaped body that was attached to the sea floor by a reed and developed two tentacles on its head used to catch food. They were the first members of a group of animals that includes modern starfish and acorn worms.
There was also a creature that the researchers called a bugle worm because of its close resemblance to that musical instrument, with a worm body attached to the sea floor and a proboscis that could end outside.
“When we collected fossils in the field, we were all amazed at how different the animals were and how many fossils there were,” Dunn said.
“We expected to see more evidence of animals in the Ediacaran, but animals like the bugle worm tell us that not all of these are going to be species that we can predict with different types of animal life or even the Cambrian explosion,” Dunn said. “This tells us that there is still much to learn about the radiation of animal life and the nature of the transition from the Ediacaran to the Cambrian.”
Reporting by Will Dunham in Washington, editing by Rosalba O’Brien
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