In 1859 Charles Darwin remarked… in On the Origin of Species: “What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”
Darwin proposed an elegant explanation: these diverse animals share this pattern because they evolved from a common ancestor that possessed limbs with digits.
But the first chapter of that story—the bit where the hand and wrist evolved from bones in the fin of an ancestral fish—has remained murky at best because scientists have lacked sufficiently complete fossils of transitional creatures between fully aquatic fish and land-roving tetrapods.
This past March we unveiled an extraordinary fossil—a complete skeleton of a 375-million-year-old fish, Elpistostege watsoni—that goes a long way toward filling that gap in understanding. The fossil preserves in its fins bones comparable to the ones that make up our fingers, showing that digits evolved before vertebrates left the water. This discovery overturns the conventional wisdom about when and how the hand evolved and shines new light on the rise of tetrapods, a pivotal event in the history of life on earth.