Monday, June 16, 2008

Dragon lizards who were born to run have a design fault

Lizards from the Outback have been put on treadmills to help scientists to determine whether it is better to run on two legs or four.

The conundrum raised in the George Orwell novel Animal Farm has perplexed zoologists since the discovery of dragon lizards that can run on two legs and on four. Researchers have speculated that it is an evolutionary advance. Others argued that it meant the animals could flee predators more quickly. Close analysis of their bodies and speed tests on treadmills have revealed however that two legs are slightly more inefficient than four. Rather than provide the animals with an advantage in the wild, the ability to rear up on their hind legs as they scuttle across the Outback is simply a design fault.

Experiments in which lizards were prompted to sprint on treadmills showed that they lifted on to their hind legs because the rate of acceleration altered their centre of gravity and made it impossible to keep four feet on the ground. They were simply accomplishing the reptilian equivalent of a cyclist’s wheelie.

Observations of how fast the lizards ran on the treadmills showed that speed could be ruled out as the cause because the animals were able to run just as fast on four legs. The theory that lifting up on two legs was an evolutionary advance and a step towards an entirely bipedal lifestyle was quashed when researchers realised that ancient species of lizard spent just as much time on two legs as the modern varieties.

Dr Christofer Clemente, of the University of Cambridge, said that rising up on their hind legs was the price that lizards had to pay for the speed and manoeuvrability that turned them into “the jet fighters of the Outback”.

He said: “I think it’s just an evolutionary accident. It’s a consequence of them wanting to run really quickly. As they are moving, it causes the front of the body to flip up. The reason we think this comes about is these lizards have adapted themselves to be really quick and manoeuvrable runners. One of the ways they do that is by moving the centre of gravity towards the back of the lizard – that makes them more manoeuvrable. A fighter jet has a centre of gravity near the back. It makes it more manoeuvrable but less stable. Boeing 747s have a centre of gravity much closer to the nose. These lizards are like the fighter jets. They are really quick, really manoeuvrable but really unstable.”

The findings by the Anglo-Australian research team, published in The Journal of Experimental Biology, also ruled out a theory that the lizards ran on two legs to breathe better. Lizards cannot take breaths when running because the muscles they use to expand and contract the lungs have to be used to move the animals forward. It had been suggested that with the front legs off the ground the muscles would be able to operate the lungs, but this was proved to be wrong.

Lizard kings

— Komodo dragons are the largest lizards. They can grow to 3m (10ft) and weigh more than 200lb (90kg)

— The fastest recorded lizard is the spiny-tailed iguana, at 33km/h

— As well as being able to change colour chameleons can rotate their eyes independently of one another

— There are more than 4,670 species of lizards

— Horned lizards scare away predators by squirting blood from their eyes

Original here

No comments: