Why bother running on hind legs when the four you’ve been given work perfectly well? This is the question that puzzles Christofer Clemente. For birds and primates, there’s a perfectly good answer: birds have converted their forelimbs into wings, and primates have better things to do with their hands. But why have some lizards gone bipedal? Have they evolved to trot on two feet, or is their upright posture simply a fluke of physics? Curious to find the answer, Clemente and his colleagues Philip Withers, Graham Thompson and David Lloyd decided to test how dragon lizards run on two legs.
But first Clemente had to catch his lizards. Fortunately Thompson was a lizard-tracking master. Driving all over the Australian outback, Clemente and Thompson eventually collected 16 dragon lizard species, ranging from frilled neck lizards to the incredibly rare C. rubens, found only on a remote Western Australian cattle station. Returning to the Perth lab, Clemente and Withers set the lizards running on a treadmill, filming the reptiles until they were all run-out.
Clemente admits that when he started, he thought that the lizards would fall into one of two groups; lizards that mostly ran on two legs, occasionally resorting to four, and lizards that never reared up. Not so. Even the lizards that he’d never seen on two legs in the wild managed an occasional few steps on their hind legs. In fact, the lizards’ propensity for running on two legs seemed to be a continuum; C. rubens and P. minor spent only 5% of the time on their hind legs while L. gilberti spent 95% up on two.
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