The Shape of Life . Bones, Brawn and Brains

From Fins to Feet: How Vertebrates First Walked on Land

Jenny Clack investigating prehistoric tetrapod tracks

It's every paleontologist's dream to find a transitional form, something that falls between two groups that we are familiar with, that sort of links them both in terms of anatomy and lifestyle. -- Jenny Clack

Video: Clack explains Boris, a fossil of an early tetrapod

At Cambridge University's Museum of Zoology, Paleontologist Jenny Clack studies how vertebrates made the transition from sea to land, from animals with fins to animals with legs. Convincing evidence that limbs evolved while tetrapods (vertebrates with four appendages) were still water-bound comes from a fossil Clack discovered in the mountains of Greenland, in 1987. She gave the 360 million year old specimen, a fossil of the creature Acanthostega, the nickname "Boris."

Her study of Boris revealed that he was a fishlike animal with limbs. "This is a specimen of an animal that could be described as a missing link, except that we have one so it's not missing," Clack says. "Its a transitional form between animals with fins that we'd call fish, and animals with legs, with fingers and toes on the end that we call tetrapods. We are tetrapods."

Clack also found evidence of early tetrapods on Valencia Island, off the southwest coast of Ireland. There, she studied the fossilized tracks an early tetrapod left in the mud of the shallows of an ancient shore. She could tell from the tracks and the surrounding rock strata that it was one of the early vertebrates to leave its footprints on land.

Valencia Island, Ireland
	Dr. Jennifer Clack Biography and Career Q & A