STUDY SUGGESTS ANIMALS EVOLVED FAR EARLIER THAN FOSSILS SHOW

Animals may have evolved hundreds of millions of years before their first undisputed fossils appear, according to a study led by the University of Oxford and published in the journal Science Advances. The research team, which also included scientists from the University of California, Berkeley, ETH Zürich and Yale University, suggests animal origins could stretch back to between 800 million and 700 million years ago, deep within the Neoproterozoic Era and possibly before or during some of Earth's most extreme ice ages. The researchers argue the patchy fossil record cannot reliably be used to fix an upper age limit on when animals first appeared. Study co-author Ross Anderson, an associate professor of natural history at the University of Oxford, said "the precise birth date of the animal kingdom remains uncertain" until further evidence emerges.

Previous estimates relied heavily on the Weng'an Biota, a roughly 590-million-year-old fossil deposit in China that preserves microscopic organisms in detail but contains none definitively identified as animals, leading scientists to infer animals had not yet evolved at that point. To test this, the team examined more than 140 samples from the Kheseen Biota in Mongolia, a site more than 40 million years younger than Weng'an that shares some species with it, using scanning electron microscopy. The survey uncovered new microfossil species, including spiny acritarchs and embryo-like fossils containing internal cells, yet none could be confidently identified as animals either, even though confirmed animal fossils are known from elsewhere, including Namibia and South China, by that time.

The researchers say gaps in the fossil record may reflect scientists searching in the wrong locations or conditions unsuitable for preservation, rather than a genuine absence of animals. One estimate places the oldest confirmed animal fossil evidence at around 574 million years old, during the Ediacaran period, which the study says could understate the true origin of animals by up to 200 million years. The findings were published on 2 October in Science Advances. The authors say further fossil discoveries will be needed to narrow down when animals first emerged.