Leaping lizards tip tails for soft landing

Jumping lizards adjust the position of their tails in mid-air to ensure a smooth landing, and certain agile dinosaurs probably did likewise. So say a team of biomechanics who put some red-headed agama lizards (Agama agama) through their paces in a laboratory. The scientists filmed the African reptiles as they jumped from a horizontal platform to a vertical wall. Slow-motion footage showed that if a lizard had to hoist the front part of its body in order to land correctly, it bent its long, slender tail upwards. By curling its tail, the lizard provided a clockwise movement that gave an anticlockwise tilt to the front of its trunk. This enabled the critter to land safely, paws-first, onto the wall. Few lizards may have known this, but they were upholding the principle of conservation of angular momentum by exploiting the moment of inertia. Tightrope walkers, too, use this principle. They correct their balance by using a long pole. It is tilted to make the body lean in the opposite direction to the tilt. The team, led by Robert Full of the University of California at Berkeley, built a lizard-sized robot car, complete with a tail controlled by gyroscopes, to see whether the lizard's agility could be replicated by technology. When the car jumped off the ramp, it started to fall nose-first, but this angle was smartly corrected by a movement of the tail, and the toy vehicle -- named "Tailbot" -- landed on its wheels. Previous research has suggested there are several species of animals that use their tail to harness the moment of inertia, including lemurs, cats and kangaroo rats. The paper speculates that small, two-footed carnivorous dinosaurs, including the velociraptor made notorious by the movie Jurassic Park, may also have done the same trick. Larger dinos, though, are unlikely to have jumped far, if calculations of their bone-to-muscle ratio are right.