Researchers Compare Computer Captures of Monitor Lizard's Running Styles

Posted on April 30, 2012

Christofer J. Clemente of Harvard University, and his team, conducted research to find why bigger animals aren't always faster. Clemente says, "Typically, bigger animals tend to run faster than smaller animals, because they have longer legs. But this only works up to a point. The fastest land animal is neither the biggest nor the smallest, but something in between. Think about the size of an elephant, a mouse and a cheetah."

Clemente and his team studied monitor lizards to show that that the same principle applies within species as well as across species. Adult monitor lizards vary substantially in size, so they are an ideal species for testing how size affects speed. The researchers timed and photographed monitors ranging from two to 12 pounds, as they sprinted across a 45-foot track. The researchers found that the midsize lizards were fastest. 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.

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

The larger lizards have to change their running style to compensate for greater weight, making them slower runners. have Take a look:

The research paper, "Optimal Body Size with Respect to Maximal Speed for the Yellow-Spotted Monitor Lizard (Varanus panoptes; Varanidae)," was published here in the May/June 2012 issue of the journal, Physiological and Biochemical Zoology.