A study puts animal origins up to 200 million years earlier
A University of Oxford-led study argues that animals may have originated between 800 million and 700 million years ago, well before the oldest definitive animal fossils. The finding revises a basic account of life’s early history, though the researchers stress that it does not prove animals existed then.
Bottom line — The study moves the estimated origin of animals back by roughly 200 million years, but definitive pre-Ediacaran body fossils remain elusive.
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The team examined more than 140 samples from Mongolia’s Kheseen Biota, finding exceptionally preserved microfossils but none confidently identifiable as animals, according to Phys.org.
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Kheseen is more than 40 million years younger than China’s roughly 590-million-year-old Weng’an deposit; the researchers say Kheseen shows that excellent preservation does not guarantee animal fossils will appear.
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The team recalculated molecular-clock estimates using geological deposits from Norway, Australia and Arizona dated to roughly 850 million to 730 million years ago, rather than relying on the younger Weng’an deposit.
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The revised estimate places animal origins before or during the Cryogenian glaciations, which began around 720 million years ago; whether animals lived through them remains unknown.
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Biomarkers have been interpreted as evidence consistent with sponges living at least 650 million years ago, Live Science reports, but they are not definitive body fossils.
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Study co-author Ross Anderson said the precise birth date of the animal kingdom remains uncertain; the researchers plan to investigate more rocks with different environments and preservation conditions.