terça-feira, 14 de setembro de 2010

Prehistoric fish fingers revealed

22 October 2007

Our hands and feet developed from prehistoric fish fingers, according to new research by a scientist at the Natural History Museum.

The small fin bones of the Australian lungfish Neoceratodus are essentially the same as fingers and toes in today's backboned land animals.

A living fossil

The Australian lungfish is known as a living fossil. It is a species that has survived since first appearing on the fossil record 100 million years ago. It is part of a group of fish called lobe-fins that are the closest living relatives of land animals.

Responsible gene

The development of fingers and toes in the embryos of land animals is closely linked to a particular gene, Hoxd13. This gene acts in a distinctive pattern in the outer part of the limb, affecting the digits, but not the arm bones.

The new research shows this gene follows an almost identical pattern in Australian lungfish, acting on the small fin bones (radials) and not the rest of the limb, providing powerful evidence that digits are the equivalents of fin bones.

Evolution from sea to land

'Where our fingers came from has been one of the biggest mysteries surrounding the move of our evolutionary ancestors from sea to land,' said Dr Zerina Johanson, palaeontologist at the Museum.

'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: fish fingers really existed.'

The study also involved researchers from Uppsala University in Sweden, Macquarie University in Australia and the Netherlands Institute of Developmental Biology. It will be published in the forthcoming issue of the Journal of Experimental Zoology.

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