The evolution of hind legs can be traced back to hind fins, researchers claim, challenging the existing theory that large, mobile hind limbs developed after vertebrates became land creatures.
The key evolutionary link - described in the Proceedings of the National Academy of Sciences - followed the discovery of a well-preserved pelvis and a partial pelvic fin from a tiktaalik roseae, a 375 million-year-old transitional species between fish and the first legged animals.
The discovery may show that the evolution of hind legs began as enhanced hind fins, scientists argue.
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The fossil was discovered in northern Canada in 2004, and showed the back part of the creature's body which contained partial pelvic fin material. The pelvis itself, although fish-like, contained hip sockets.