New research from the University of Oxford challenges the timeline of animal evolution by questioning the use of specific fossil deposits to date the origin of the animal kingdom.
Key facts
- •The study was led by the University of Oxford with researchers from UC Berkeley, ETH Zürich, and Yale University.
- •Researchers analyzed over 140 samples from the Kheseen Biota in Mongolia using scanning electron microscopy.
- •Molecular clock analysis suggests animal origins occurred 800 to 700 million years ago, rather than after 590 million years ago.
- •Chemical biomarkers have previously provided evidence consistent with sponges living at least 650 million years ago.
- •The study notes that early animals were likely small and soft-bodied, making them difficult to preserve in the fossil record.
A study led by the University of Oxford suggests that animals may have evolved hundreds of millions of years earlier than the fossil record currently indicates. Published in Science Advances, the research challenges the assumption that the absence of animal fossils in certain ancient deposits proves they did not yet exist. The findings indicate that animal origins may date back to between 800 and 700 million years ago, potentially predating extreme ice ages in Earth's history.
By the numbers
Challenging Fossil Record Assumptions
Scientists have previously used the 590-million-year-old Weng'an Biota in China as a benchmark to argue that animals originated after that time, assuming the deposit's exceptional preservation would have captured them if they existed. However, researchers examined the Kheseen Biota in Mongolia, which is more than 40 million years younger than Weng'an and contains similarly well-preserved microfossils. Despite this, the Kheseen samples show no evidence of animals, even though animals are known to have existed elsewhere by that time.
Revised Evolutionary Timeline
By using older geological constraints from deposits in Norway, Australia, and the United States, the team applied molecular clock analysis to estimate the origin of animals. This method, which compares genetic differences between living species, shifted the estimated origin back by approximately 200 million years. This suggests animals may have appeared between 800 and 700 million years ago, potentially during or before the Cryogenian Period's 'Snowball Earth' ice ages.
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This article was independently rewritten by ManyPress editorial AI from reporting originally published by Phys.org.
