Researchers from the University of Cambridge and the Royal Veterinary College said our understanding of the anatomy of the first four-legged land animals, known as tetrapods, has been wrong.
New 3-D models of fossil remains using high-energy X-rays to create computer reconstructions show parts of the spine previously thought to face the front in fact faced the back, and vice versa, the BBC reported Monday.
"Their vertebrae are actually structurally completely different from what everyone for the last 150 or so years has pictured," John Hutchinson of the veterinary college said. "The textbook examples turn out to be wrong."
The researchers said the new anatomical findings supported the thesis tetrapods dragged themselves out of the sea using their front legs, dragging the rest of their body along the ground in the same way seals get around on land.
"All of that anatomy was handed down to later animals," Hutchinson said.
"It influenced the future evolution of the spine in everything on land. It tells us about our own development and why our own backbones developed they way they did."