Reconstructing dinosaurs from ancient DNA has been dealt a blow with a new study finding genetic material can only last 1 million years.

An international team of researchers reached the finding after analysing DNA extracted from bones of the extinct New Zealand moa.

They found that while short fragments of DNA could possibly survive up to 1 million years, sequences of 30 base pairs or more would only have a half-life of around 158,000 years under certain conditions.

Lead author Dr Morten Allentoft from Murdoch University's Ancient DNA lab in Perth says their results contradict earlier studies which claimed to have extracted DNA fragments several hundred base pairs long from dinosaur bones and preserved insects, claims which underpinned the storyline of the 1993 movieJurassic Park.

"What we show here with the decay rate of DNA is that this is never going to be possible," Dr Allentoft said.

"It may be that you can have extremely short fragments of DNA, only a few base pairs that persist for maybe a million years, maybe even longer."

Dr Allentoft says the earlier findings may have been due to contamination with human DNA.

Rate of decay

The latest study, published in the Proceedings of the Royal Society B, also establishes a DNA decay rate which could help identify specimens likely to yield useful genetic material.

It might also one day enable DNA to be used to date bones and teeth or even be used for forensic investigation of human remains.

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DNA dating study kills off Jurassic Park