A zigzag engraving on a mussel's shell may transform scientific understanding of what has long been considered a defining human capacity: artistic creativity.

Until now, the earliest evidence of geometric art was dated from 70,000 to 100,000 years ago. Scratched into rocks found in South African caves, those engravings signified behavioral modernity: Homo sapiens' unique cognitive journey into a sophisticated world of abstraction and symbol.

But new analysis of an engraving excavated from a riverbank in Indonesia suggests that it's at least 430,000 years old—and that it wasn't made by humans, scientists announced Wednesday. At least it wasn't made by humans as most people think of them, meaning Homo sapiens.