Walk this way

日期:2017-07-23 04:41:03 作者:柯攵 阅读:

By Jon Copley WATCHING alligators running on a treadmill has helped biologists to debunk a theory about their ancestry. Instead of inheriting their gait from primitive lizards and amphibians, alligators and crocodiles may have acquired the way they move from an ancestor that walked like a cat or dog. Primitive lizards and amphibians walk with their legs jutting out sideways from their bodies in a posture known as a “sprawl”. But mammals walk with an erect posture, with their legs under their bodies, as did the dinosaurs. Alligators and crocodiles were thought to represent the missing link between these two types of locomotion, as they use a “high walk” halfway between sprawling and walking erect. To take a detailed look at how alligators move, Stephen Reilly and his student Jason Elias at Ohio University in Athens painted reflective dots on the joints and limbs of alligators then filmed them running on a treadmill under a strobe light. They used a mirror to view them simultaneously from above and the side. They then constructed a three-dimensional computer model of how the alligators moved (The Journal of Experimental Biology, vol 201, p 2559). Animals usually increase their speed by moving the upper parts of their legs more quickly. However, the researchers found that when alligators speed up they straighten their legs at the knee, effectively giving them longer legs and lengthening their stride. They also extend their ankles faster to generate more propulsion. “The knee movements of the gator `high walk’ are different from the true sprawlers,” says Reilly. This suggests alligators and crocodiles may not have evolved from lizards or amphibians. It adds weight to fossil evidence supporting an alternative ancestry, says Mason Meers, an evolutionary biologist and anatomist at Florida Gulf Coast University in Fort Myers. “The very basal ancestor of the modern crocodilians may have walked fully upright,