ROCKS in Newfoundland that are 575 million years old have revealed the earliest animal fossils yet discovered. The animals are 2 metres long 鈥� defying palaeontologists鈥� ideas about when the first anatomically complex multicellular animals evolved.
The newly discovered ancient creatures lived just 10 million years after what appears to be the last in a series of devastating ice ages, known as 鈥淪nowball Earth鈥�, supposedly froze the planet and killed off almost all life. The discovery suggests either that early animals evolved amazingly fast after the ice melted, or that the ice did not cover the whole planet.
Only small, very simple fossils have been found from before Snowball Earth, and many believe that the snowball created a bottleneck that allowed the evolution of more complex life forms once it ended, 585 million years ago. The earliest large animal fossils known until now appeared 20 million years later. They are flat, soft-bodied animals called the Ediacaran fauna.
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Now Guy Narbonne of Queen鈥檚 University in Kingston, Ontario, and Jim Gehling of the South Australian Museum in Adelaide have searched rock deposits in Newfoundland 575 million years old, looking for even earlier examples of the Ediacarans, which they expected to be simpler forms of multicellular life, perhaps primitive discs left by simple colonies of cells. But that is not what they found.
鈥淭he oldest Ediacaran fossils in the world are the biggest,鈥� Narbonne told 快猫短视频.
Narbonne and Gehling found four species, including narrow frond-like structures they named Charnia wardi that stretched up to 2 metres long. These were filter-feeders that were attached upright to the ocean floor until ash from a volcanic eruption killed them and squashed them into the seabed (Geology, vol 31, p 27).
Narbonne was surprised to find the new fossils were alive only 10 million years after the ice ages ended. 鈥淭hese guys are too complex to have arisen in 10 million years,鈥� he says, unless evolution worked exceptionally fast. He thinks it more likely that the final snowball glaciation did not cover the whole planet, but left open an area that allowed the Ediacaran fauna to evolve before the freeze ended.