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When Did Animals First Evolve? New Evidence From Mongolia Suggests It Could Be As Far Back As 800 Million Years Ago
The earliest definitive animal fossils date to roughly 560 million years ago. But because these organisms are already multicellular and somewhat complex (despite lacking some trivial things like a mouth or gut), their true origin is thought to be older still. However, researchers hunting for fossils of these more ancient animals have so far come up empty handed. That's despite some fossil sites showing exceptional preservation that should, in theory, have captured any simple animals that were swimming about. One of these is a site in China known as the Doushantuo Formation, which contains an assemblage called the Weng’an Biota. Dating back around 590 million years, it preserves an incredible snapshot of microscopic marine organisms in three dimensions. And yet, despite the near-perfect level of preservation, there is no evidence of animal life. This has been used to argue that animals must have evolved during the 30-million-year gap between the Weng’an Biota and the first definitive animal fossils. Now, however, new evidence from a fossil assemblage in Mongolia called the Kheseen Biota is challenging that interpretation. Like Weng’an, the Kheseen assemblage contains an astonishing array of well-preserved marine organisms without a single animal fossil. But there is one key difference:...