Inside the stout fins of a fish that, about 380 million years ago, prowled the shallow waters of an estuary in what is now eastern Canada, scientists have found what they call the evolutionary origins of the human hand.

The researchers were examining a remarkably complete fossil of a fish called Elpistostege watsoni. It represents a pivotal stage in a landmark event in the history of life on Earth — the transition of fish to land vertebrates.

For this to occur, anatomical changes were needed including the evolution of hands and feet. Inside the tip of Elpistostege's front fins, called pectoral fins, were tiny bones. Known as radial bones, they were arranged in a series of rows like digits — the precursor to fingers. They would have provided the flexibility for Elpistostege's fin to bear weight on land.