A piece of fossilised bone just a centimetre long and around 240 million years old is providing evidence that a line of giant lizards still living in New Zealand can trace their ancestry back to beyond the time of the dinosaurs.

The jaw bone was not dug up in New Zealand but in Vellberg in Germany.

The find pushes back the history of the New Zealand animal, the tuatara, by a further 10 to 15 million years.

Rainer Schoch of the Stuttgart Natural History Museum said in the magazine BMC Evolutionary Biology that the find, along with later discoveries including a complete skeleton, would provide further knowledge on the evolution of this line of reptiles.

They are related to both snakes and monitor lizards.

The species, which measured between five and 10 centimetres, has the unusual characteristic of the teeth growing directly out of the jaw. "Our early specimen is a very complete tuatara," Schoch said.

Tuatara, often described as "living fossils," continue to live on several islands off the New Zealand coast.

"I don't like the term 'living fossil' but this is the case here to some extent. This line is very long and very conservative," Schoch said.

The site in south-western Germany has yielded more than 25 new species over the past 13 years. Schoch hopes that many more will be found in the rocks.

The biggest finds at Vellberg range up to six metres in length.

Palaeontologists from Washington, Buenos Aires, London and Berlin are assisting with the dig.