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Four Legs Good, Two Legs Better for Hurdling Obstacles

By Elizabeth Preston
Feb 6, 2016 1:00 AMNov 20, 2019 3:50 AM


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Although lizards mostly scurry on all fours, certain species can run on two legs when the mood strikes. What's the benefit to this human-like running style? For one thing, it seems to let lizards get over obstacles without slowing down. They just have to make sure not to tip over. Georgia Southern University biologist Lance McBrayer and graduate student Seth Parker studied running in a handsome little reptile called Sceloporus woodi, or the Florida scrub lizard. McBrayer says there's been a lot of research into lizard species that always run on two feet. But lizards that switch between a two- and four-legged stance while running are more mysterious. Some scientists have suggested that it's just a product of the lizards' long bodies and acceleration—in other words, that they're forced up onto their back legs like an airplane near the end of its runway. McBrayer and Parker trapped four dozen wild lizards from the Ocala National Forest in Florida. They brought the lizards, all male, back to the lab. There, they put the lizards onto a miniature, rectangular racetrack. The track was built out of wood, with packed sand on its floor. Some lizards simply ran down this course while a high-speed camera recorded their steps. Other lizards had to contend with obstacles. The researchers added either one or two little wooden barriers along the length of the track. The lizards weren't naturally motivated athletes, though. Researchers had to chase them down the track, clapping their hands or tapping the lizards' tails to keep them moving. If a lizard managed to sprint a full meter without stopping, the researchers counted it as a success. Here's a video of one of the lizards bounding over obstacles on two legs. The top of the image is a mirror that gives a better view of its running stance: https://youtu.be/sf2Ks-LyOKE Lizards that used a two-legged stride during their run down an obstacle course finished faster than lizards that only ran on four legs. Lizards that used two legs were also more likely to clear an obstacle without stepping on it. When they ran bipedally, the lizards held their long tails out low, for balance. McBrayer says the results suggest that Florida scrub lizards are in control of when they run on two legs. It's not just an involuntary byproduct of going fast. In other research, he says, he's seen that the lizards use a distinctive step pattern when clearing an obstacle on two legs—not unlike a human hurdler during a race. Running on two legs when they feel like it may let Florida scrub lizards sprint through cluttered environments quickly and efficiently. Meanwhile, this lizard is just showing off: https://youtu.be/45yabrnryXk?t=48s

Image: by Bob Peterson (via Flickr)

Parker, S., & McBrayer, L. (2016). The effects of multiple obstacles on the locomotor behavior and performance of a terrestrial lizard Journal of Experimental Biology DOI: 10.1242/jeb.120451

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