Tuatara may have been first vertebrates to run

A tuatara at Karori Wildlife Sanctuary in Wellington. File picture / Mark Mitchell

American researchers studying New Zealand's tuatara at an Ohio zoo say the creatures were the first vertebrates to not only walk the Earth, but to run on it as well.

"Tuataras are the oldest living models of early tetrapods (four-legged animals) still alive today; that's what makes them so interesting," said Stephen Reilly, associate professor of biological sciences at Ohio University.

The study at Toledo Zoo found tuatara both walk and run -- an energy-saving strategy previously thought to be important only in fast-running animals such as mammals and birds.

Fossil records have shown that the tuatara were running as long ago as 225 million years and have not changed significantly over time.

"I would really like to study their locomotor behaviour in the wild," Dr Reilly said.

"Given their status as the world's oldest known living tetrapod, knowing more about how these animals move in nature is critical to our understanding of vertebrate evolution."

In the research, just published in the scientific journal Proceedings of the Royal Society B (Biological Sciences), the Toledo team measured tuatara and salamanders on a high-tech running track that measured the force with which their feet hit the ground with each step.

By studying videotapes and the measurements of the impact that the tuatara feet made, the researchers could tell when the animals were walking or running.

Their slow, lumbering gait -- which until now had led scientists to believe that the primitive animals could only walk -- was revealed by the force data to include running.

In walking, the centre of mass vaults up and over the limbs with each step, but in running, the centre of mass dips with each step, and tendons and joints in the legs act as biological springs.

Mammals such as humans, dogs and horses can use both mechanisms to conserve up to 50 per cent of their energy needed to walk and run.

The researchers spotted the telltale vault and dip of centre of mass movements in different strides -- confirmation that the tuatara mechanically walk and run.

Because they are the oldest living examples of four-legged animals, the new findings suggest that both energy saving mechanisms appeared when the first vertebrates moved on to land, Dr Reilly said.

The important implication is that all terrestrial vertebrates -- except for turtles, which are limited by their shell -- can walk and run.

But the researchers also showed that tuatara were not saving much energy by switching between walking and running -- they moved at about the same speed and used about the same amounts of energy.

Dr Reilly said this could indicate that despite the pre-adaptation for two gaits, the primitive animals never evolved the need for speed, unlike other animals.

- NZPA