Fish fingers: how our limbs came from fins

6 April 2006

Fossil-hunting scientists have unearthed the remains of the very first fish out of water, showing how our limbs evolved from fins in the distant past. Is this the 'missing link' between water and land animals? Antenna digs deeper...

This story was published in Nature on 6 April 2006.

Neil Shubin holds parts of the newly discovered fossil, the preserved remains of a creature that helps fill the evolutionary gap between fish and land animals.

Image: Dan Dry

The icy desert of the Canadian Arctic has surrendered startling evidence of evolution in action - the preserved skeleton of a fish that's half amphibian.

After six years of searching, scientists have now made an extraordinary find - the first ever fossil of a creature with scales and fins like a fish, but also wrists, fingers, ribs and a neck like a land animal.

The fossil was discovered on Ellesmere Island, one of the northernmost pieces of land in Canada.

Image: Neil Shubin

Experts think that the first land animals evolved from fish a mind-boggling 360 million years ago. But until now they had no rock-solid proof of how limbs came from fins because they hadn't found a fossil clearly showing the in-between stages.

'If you look inside the fin of this new fossil you find the bones of our arms and parts of our hand. We found the shoulder, the upper arm, the elbow, the forearm, what looks like the wrist and things that look like fingers.'
Neil Shubin, fossil expert, University of Chicago

Neil Shubin, University of Chicago

Image: Dan Dry

Experts have built a model of the new species, called Tiktaalik roseae, to show what they think it looked like when it was alive.

Image: Beth Rooney

The creature might have looked like this model - it's well on the way to becoming a land animal. It probably lived in shallow streams in a large swampy river delta, occasionally crawling out of the water for a breath of fresh air.

How important is this fossil?

'We're talking about a piece of our own history here. This find supports the idea that major pieces of all creatures that live on land originally evolved in fish living in ancient streams.'
Neil Shubin

Image: Ted Daeschler

'It's the best fish fossil found so far to show how the first four-legged animals evolved. It's absolutely fantastic - it confirms everything we thought and also tells us about the order in which certain changes occurred.'
Jenny Clack, expert on land-animal evolution, University of Cambridge

Jenny Clack, University of Cambridge

Image: Jenny Clack

Neil Shubin and his fellow fossil-hunters endured 24-hour daylight and hungry polar bears high up in the Canadian Arctic before unearthing the remarkable fossil of a creature halfway between a fish and an amphibian.

They didn't have to dig very deep - there's no dirt, shrubs or trees covering the land so ancient bones are easily found as wind and rain wear away the rocks.

The fossil-hunters camped in the Canadian Arctic for up to six weeks at a time, hundreds of miles from the nearest human settlement.

Image: Neil Shubin

A striking feature of the fossil is that it has fins with the same joints as our limbs. It has a working wrist, so its fin can lie flat against a surface like a hand and support its body. But that's not the only way it's different from a fish.

'This thing clearly had gills, but we also found very good evidence that it had lungs too. And its ribs fit together in a certain way that supports its body under gravity like a land animal.'
Neil Shubin

Image: Kalliopi Monoyios

'This creature has lost the bony flaps that fish have covering their gills. There was always a question about when that happened - this shows it was before these animals lived on land.'
Jenny Clack

The world was a very different place when the creature was alive, 375 million years ago. North America was attached to Europe in a huge landmass that straddled the Equator, and the climate was dramatically different.

'Here I am, standing at the base of a glacier, looking out onto the Arctic landscape, and I'm cracking open rocks that contain tropical fish.'
Neil Shubin

The scientists had to work through snow and sleet and carried shotguns to ward off hungry polar bears.

Image: Neil Shubin