Lungfish provides clues about digit development

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How land animals developed digits (fingers and toes) as they evolved out of water has long been a mystery.

However, new research carried out at the Natural History Museum in London has for the first time made a link between the development of digits in land animals and the development of fins in fish.

Palaeontologist Dr Zerina Johanson has linked the development of small fin bones, known as ~radials , in the Australian lungfish, Neoceratodus forsteri, with the development of digits in land animals.

The link is a gene called Hoxd13, which had previously been strongly linked with the development of digits in land animals. It was identified as distinctively acting only on the digits, and not on the rest of the arm, however no evolutionary link was made.

Johanson has now found that the gene works in an identical way in the lungfish, and codes only for the radials, and not the rest of the fin.

The research suggests that it is from radials similar to those found on the fins of the Australian lungfish that our fingers and toes first began to evolve. This means that what had appeared to be a dramatic difference between fish and land animals can now be seen in more gradual evolutionary steps.

Where our fingers came from has been one of the biggest mysteries surrounding the move of our evolutionary ancestors from sea to land, said Johanson.

Small fin bones are found in all the fossilised lobe-fins that fall in the evolutionary journey between lungfish and land animals, suggesting that digits evolved gradually. Hands aren't as uniquely evolved as we thought.