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Lizard puts man in the shade with ability to walk on water

Walking on water is scientifically possible, two American researchers have established, but only lizards can do it - and the lizards are really walking on air.

Dr J W Glasheen and T A McMahon, of Harvard University, captured seven basilisk lizards in Costa Rica and put them (literally) through their paces in a glass water tank in the laboratory. These lizards are well known for their ability to "run" on water - not swimming, but not sinking either.

In fact, the researchers found that the lizards do not run on the water. They do slap their feet down flat on to the surface, but most of the support for their weight comes from bubbles of air sucked in behind the foot as it strokes downwards like a swimmer in the water.

The lizards get their feet out quickly, before the air bubbles collapse. They move at such a speed they can lift their legs and continue across the water before the cavity of air disappears.

But the ability to run across water is bought at an enormous expenditure of energy. The little lizards, which weigh just 90g, have to develop a mechanical power of about 29 watts per kilogram of bodyweight. The maximum sustained output that a human being can manage - say a fell runner going uphill - is about 20 watts per kilogram.

The lizards have such powerful backlegs the researchers estimate they could manage 135 watts per kilogram and that "at least 21 per cent of the basilisk's body mass is involved in powering hind limb motion".

Humans are also stopped from running across water by the size and shape of our feet and legs, and the maximum speed with which we can run. To move on before each bubble of air collapsed, a human water runner would need to stroke downwards through the water at almost 30 metres a second - beyond human ability.