Washington, June 13 : While studying how dragon lizards run on two legs, a team of researchers has realised that there is a strong correlation between the lizards' acceleration and their front legs pulling off the ground.
Christofer Clemente, a zoologist at the School of Animal Biology affiliated to the University of Western Australia, revealed that he and his colleagues collected 16 dragon lizard species for their study.
He said that the lizards collected ranged from frilled neck lizards to the incredibly rare C. rubens, found only on a remote Western Australian cattle station.
Thereafter, he added, the lizards were made to run on a treadmill, and simultaneously filmed until they were all run-out.
Clemente said that while beginning the study, he had thought that the lizards would fall into one of the two groups-those that mostly ran on two legs, occasionally resorting to four, and those that never reared up.
However, the footage of the lizards running on the treadmill showed that even those lizards managed an occasional few steps on their hind legs that Clemente had never seen on two legs in the wild.
The researchers observed that C. rubens and P. minor spent only 5 per cent of the time on their hind legs, while L. gilberti spent 95 per cent up on two.
Clemente's team drew up the lizards' family tree, and plotted on the percentage of time each species spent on their rear legs, but there was no correlation.
He said that the reptiles had not evolved to move on two feet, and that something else was driving them off their front legs.
When the researchers even analysed whether running on two legs was faster or more economical than running on all four, they realised that running on hind legs was more energetically costly, and the bipedal runners were no faster than the quadrupeds.
Clemente then decided to test a suggestion that lizards improved their manoeuvrability by moving their centre of mass back towards the hips, in order to determine whether the lizards' front legs were leaving the ground because of the position of their centre of mass.
He and his colleagues modelled the running lizards' movements as they accelerated, and found a strong correlation between their acceleration and their front legs pulling off the ground.
Clemente said that by moving their centre of mass, a turning force acts on the lizards' torso and lift's it off the ground making them run upright.
Based on their observations, the researchers came to the conclusion that running on two legs is a natural consequence of the lizards' acceleration.
"Some dragon lizards have exploited the consequence and chosen to go bipedal because it gives them some advantage, but we have no idea what that advantage is," Clemente said.