In Mongolia there is a rock that preserves microfossils exceptionally well. It is called the Kheseen Biota and it formed between 550 and 526 million years ago, when animals certainly existed. It holds no definite animal.
That absence is the starting point of a study by Orin Lole Durbin, Eliel Anttila, Derek Briggs, Francis Macdonald and Ross Anderson, published in Science Advances on 2 October 2026. Lole Durbin is first author. Anderson, of the Museum of Natural History at the University of Oxford, leads the work. The team includes researchers from Berkeley, ETH Zurich and Yale.
The problem is one of dates. Lipid biomarkers, fossil molecules left by cell membranes, point to animals before 635 million years ago. Body fossils go back no further than 574 million. Between the two lies a gap of about sixty million years with no visible animal.

Molecular clocks are meant to bridge it. Differences in the DNA of living species build up over time, and counting them dates the split between two lineages. The clock has to be calibrated with fossils. A fossil fixes a group’s minimum age, because the group existed when that organism died. A maximum age is harder to set. It needs a deposit where animals would have been preserved had they been there, and where they are missing.
For years that role went to the Weng’an Biota in China, dated by the University of Oxford press release to about 590 million years. Weng’an preserves microfossils in fine detail and contains no definite animals. Many analyses took it as a ceiling, with no animals before Weng’an.

The team compared Weng’an with Kheseen. The two sites share similar preservation and similar microfossils, and neither shows a definite animal. Kheseen, though, is more than 40 million years younger and dates from a time when animals were undoubtedly around. If they are invisible at Kheseen, their absence at Weng’an proves nothing. The ceiling goes.
In its place the authors propose several older deposits from the Tonian period that preserve both non-animal fossils and biomarkers. According to the press release these are the Svanbergfjellet Formation in Norway, the Bitter Springs Group in Australia and the Chuar Group in Arizona, between 850 and 730 million years old. The same names appear in the files the authors deposited in Dryad, the public data archive. With these limits the clock, run in the MCMCTree software, places the origin of animals between the late Tonian and the mid-Cryogenian, roughly 800 to 700 million years ago.
That window precedes or overlaps the great Cryogenian glaciations, the so-called Snowball Earth, which began about 720 million years ago. If the estimate holds, animals appeared before that ice or during it.

The authors do not claim 800-million-year-old animals. Lole Durbin says so in the press release: the analysis “does not prove that animals existed”. The paper is an argument about calibrating the clock. The date it produces depends on the rock chosen as the limit, and the article discusses that uncertainty. The release adds that early animals were probably small and soft-bodied, poor candidates for fossilisation.
ScienceDaily’s headline speaks of 200 million years earlier than thought. The figure holds only as a loose estimate. Between the clock’s window and the oldest body fossils lie 126 to 226 million years, depending on which end is taken. Against the biomarkers the gap is 65 to 165 million. Funders include NASA, the Royal Society and the ETH Zurich Foundation. Anderson concedes that the birth date of the animal kingdom will stay uncertain until older fossils turn up.

References
Lole Durbin O.M., Anttila E.S.C., Briggs D.E.G., Macdonald F.A., Anderson R.P., "Re-evaluating molecular clock maximum age calibrations revives pre-Ediacaran divergence estimates for animals", Science Advances, 12, 40, published online 2 October 2026, open access (CC BY). doi: 10.1126/sciadv.aeg6289
Lole Durbin O.M., Anttila E.S.C., Briggs D.E.G. et al., "Data from: Re-evaluating molecular clock maximum age calibrations revives pre-Ediacaran divergence estimates for animals", Dryad, 20 August 2026. doi: 10.5061/dryad.tqjq2bwfd
University of Oxford, press release "New study suggests animals may have evolved vastly earlier than fossil evidence suggests", 2026.


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Past Editor-in-Chief Italian Journal of Dermosurgery