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| Mongolian Base Camp |
How do you find the beginning of a story when its opening pages may never have been preserved?
A study published in Science Advances on 2 October 2026 brings that question into sharp focus. Led by Orin M. Lole Durbin and colleagues, the research suggests that animal origins could extend back roughly 800–700 million years—considerably earlier than their widely accepted body fossil record.
Crucially, this is an estimate from evolutionary analyses, rather than the discovery of an 800-million-year-old animal. The distinction matters. Deep time already has enough mysteries without us accidentally issuing a birth certificate.
Consider what a fossil actually tells us. A recognisable animal preserved in dated rock establishes that its kind existed by that time. It does not necessarily reveal when the lineage first evolved. Your oldest surviving family photograph works much the same way: it records someone’s presence on a particular occasion, without marking the beginning of the family.
An empty photograph is trickier. Was nobody there, or was the camera pointing elsewhere?
For palaeontologists, that is a serious question.
In China, the approximately 590-million-year-old Weng’an Biota preserves microscopic organisms with remarkable detail, yet contains no definitive animals. Its apparent silence has been used to help limit how far back animal origins could extend. The reasoning depends on an assumption: animals living then would have been preserved and recognised in those deposits.
Enter Mongolia, carrying a rather awkward piece of evidence.
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| Mongolia's Lake Khövsgöl |
The Kheseen Biota comes from northern Mongolia, where rocks of the Kheseen Formation crop out in a discontinuous belt stretching roughly 250 kilometres along the western side of Lake Khövsgöl.
These rocks record a world very different from the lake landscape we see today: an ancient marine basin where carbonate sediments, mud and phosphate-rich deposits accumulated.
Within those phosphatic rocks, microscopic organisms were preserved in extraordinary detail, leaving a tiny window into an ocean that vanished more than half a billion years ago. It is a wonderfully humbling contrast—a vast geological landscape holding some of its most revealing secrets at a scale smaller than a grain of sand.
Its preservation and microscopic inhabitants resemble those of Weng’an. It, too, lacks definitive animals.
But here is the delicious complication: animals unquestionably existed somewhere in the world during that younger interval. Their absence from Kheseen cannot mean that the entire animal kingdom had yet to evolve.
It is rather like inspecting a beautifully preserved guest list from a gathering of botanists and concluding that nobody on Earth was a dentist.
The record may be excellent. The sample may still be selective.
Kheseen’s missing animals could reflect the environments represented, the conditions of preservation, or a combination of factors. Whatever the explanation, the comparison weakens the argument that Weng’an’s missing animals provide a dependable limit on animal origins.
This is where living animals enter our fossil detective story.
Researchers can compare genetic differences among species and use evolutionary models, anchored by fossil evidence, to estimate when their ancestral lineages separated. This approach is called a molecular clock.
Think of it as a clock that requires careful setting. Fossils supply reference points; assumptions about the oldest plausible ages also influence the answer.
The team tested older geological constraints in these analyses. Their results supported an origin for animals approximately 800–700 million years ago, demonstrating how strongly the estimated timing depends on the maximum ages supplied to the models.
That possibility takes us towards an extraordinary chapter of Earth history. The interval overlaps the approach to, and beginning of, the Cryogenian Period, associated with the immense glaciations popularly called Snowball Earth. Animal beginnings might therefore belong to a world entering some exceptionally dramatic climatic upheavals.
Imagine the challenge of finding such an ancient beginning. We are asking rocks to preserve something recognisable, survive geological upheaval, become exposed where someone can investigate them, and then yield a clue we know how to read.
A demanding filing system, geology.
The next step is to keep searching across different ancient environments and kinds of preservation, bringing body fossils, traces of activity and chemical evidence into the conversation. The precise age of animal origins remains unresolved.
For me, that uncertainty is part of the wonder.
Every fossil is a surviving fragment of a much larger world. Sometimes the most compelling discovery is realising how much of that world could still be missing.
The opening pages of our animal story may be out there.
We are learning where—and how—to look.
Image: Mongolia's Lake Khövsgöl by sayursaying.com
