From: Andy Soos, ENN
Published May 1, 2012 04:17 PM

The Fastest Animal

How fast can an animal run. Speed is important for running away as well as catching up. The fastest land animal is neither the biggest nor the smallest, but something in between according to new research by Harvard University. Clemente (Harvard) and his team studied monitor lizards to show that that the same principle applies within species as well as across species, and to identify why this is the case. Because adult monitor lizards vary substantially in size, they are an ideal species for testing how size affects speed. The researchers timed and photographed monitors ranging from two to 12 pounds, as sprinted across a 45-foot track.

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The cheetah is usually considered the fastest land animal and is able to achieve speeds upwards of 70 miles per hour. It cannot, however, maintain this speed for very long, and prey that has a bit of luck can "wear down" the cheetah by avoiding it for about 10-15 seconds. The Cheetah may be the fastest running animal reaching speeds of up to 75 mph but its speed of movement is small in comparison with the Eastern Diamondback Rattlesnake with documented strike speeds of 175 mph.

The researchers found that the midsize lizards were fastest—and they discovered why.

Using high-speed cameras and markers placed at key spots on the lizards' bodies, the researchers created computer models comparing characteristics of the lizards' running strides.

"We then looked at how the mechanics of the stride changed with body size, and we found that the changes in the stride were consistent with the changes in speed," Clemente said. "Above a certain size, lizards were changing the way they ran, perhaps due to a decreased ability of the bones and muscles to support a larger body mass."

Testing this phenomenon within a single species helps clear up questions about why the biggest animals aren't the fastest. Large animals tend to be closely related evolutionarily. So it's hard to tell whether slower speeds are due to biomechanical issues stemming from size, or from any number of other factors stemming from a shared evolutionary history.

Looking at individuals within a species rather than making cross-species comparisons helps to eliminate this phylogenetic bias. The results bolster the hypothesis that large size creates biomechanical constraints.

"Larger lizards' legs can no longer support their body weight, and they have to change their style of running, making them slower," Clemente said.

So big animals are not the fastest but something similar and smaller (mid-size) may well be the fastest.

See Fast Lizard for further information

Cheetah image viaWikipedia

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