Overview
- The study, published Friday, Oct. 2, 2026, in Science Advances reports electron-microscope analysis of more than 140 Kheseen Biota samples from Mongolia that show exquisitely preserved microfossils but no identifiable animal remains.
- The authors compare Kheseen to the well‑known Weng'an deposits and say both show that high‑quality preservation can still miss animals, so using Weng'an as a strict upper age limit for animal origins is unreliable.
- When the team reran molecular‑clock analyses using older geological calibration points from 850–730 million year old deposits, their estimates shift the plausible origin of crown‑group animals back to about 800–700 million years ago.
- The researchers stress this result is not proof that animals lived then and note independent sponge biomarkers dated near 650 million years ago and preservation bias leave the question open, so they call for targeted searches in varied rock types and more data.
- If animals did arise in the 800–700 million year window it could place their origin before or during Cryogenian glaciations, which would change how scientists think about early animal survival, evolution, and where to look next for fossil evidence.