Scientists have been able to reconstruct, for the first time, the intricate three-dimensional structure of the backbone of early tetrapods, the earliest four-legged animals. High-energy X-rays and a new data extraction protocol allowed the researchers to reconstruct the backbones of the 360 million year old fossils in exceptional detail and shed new light on how the first vertebrates moved from water onto land. The results are published 13 January 2013 in Nature.

"For more than 100 years, early tetrapods were thought to have vertebrae composed of three sets of bones - one bone in front, one on top, and a pair behind. But, by peering inside the fossils using synchrotron X-rays we have discovered that this traditional view literally got it back-to-front," says Stephanie Pierce who is the lead author of the publication.

This unexpected discovery supports recent work by Pierce and Clack that showed Ichthyostega probably moved by dragging itself across flat ground using synchronous 'crutching' motions of its front legs - much like that of a mudskipper or seal. It is said that the results of this study force us to re-write the textbook on backbone evolution in the earliest limbed animals.